Chapter 1. THE LIGHT General remarks Wave characteristics Frequency spectrum Dual nature of light...

Transcription

1 Chapter 1. THE LIGHT 1.1. General remarks Wave characteristics Frequency spectrum Dual nature of light LIGHTING ENGINEERING

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3 Chapter 1. THE LIGHT 1.1. General remarks It is well known that there are several types of energy: mechanical, thermal, electrostatic and electromagnetic. If mechanical energy is applied to a body at rest, it tends to set into motion, thus, transforming the energy applied into kinetic energy. This energy is taken along and is also transmitted to other bodies, in case it collides with them. Heat is a form of energy which diffuses through convection, conduction or radiation. When a switch is "turned on", the metallic filament of an incandescent lamp is connected by means of a potential difference. Thus, electric charge flows through the filament in a similar way pressure difference in a hosepipe makes water flow through it. Electron flow constitutes the electric current. Current is usually associated to charge movement in bridge conductors, but electric current emerges from any charge flow. When electric current diffuses through conductors and reaches a receptor, this receptor is transformed into another type of energy. If the body or the emitting source irradiates energy, propagation takes place by means of radiation in the form of waves* which are those physical disturbances which diffuse in a certain medium or in the vacuum. Mechanical waves diffuse this kind of energy through an elastic material medium. They are longitudinal sound waves because particle vibration coincides with their propagation direction. Two examples of this phenomenon are vibrations of spring and sounds. In a spring, vibrations propagate in only one direction. In the case of sound, vibrations propagate in three different dimensions. Electromagnetic waves propagate the energy produced through oscillations of electric and magnetic fields and do not need a propagation material medium. For example, the light. Out of the different ways waves propagate, there are several regimes. From the point of view of lighting engineering, the periodical regime is the one which interests us. It may be defined as regular time interval repetitions and expressed graphically as several wave forms. Thus, wave form represents oscillations as phenomena in which physical quantity is a periodical function of an independent variable (time), whose average value is null. That is to say, we are talking about simple or fundamental harmonic functions, like the sine or the cosine, of a single, one-dimensional and transversal variable (propagated perpendicularly to the direction in which particles vibrate). In short, there is a wide range of physical, electric and electromagnetic phenomena, among which electricity, light, sound, hertzian waves or sea waves are included. Their characteristics are determined by studying sine waves. This is the reason why the concept of wave radiation and characteristics to define them is used Wave characteristics Wavelength ( ) It is defined as the distance travelled by a wave in a period. For a transversal wave, it may be defined as the distance between two consecutive maximums or between any other two points located in the same phase (Fig. 1). λ λ λ λ Figure 1. Wavelength. * Wave: Graphic expression of a periodic variation represented in amplitude and time. Amplitude is the maximum value or ordenate taken by the wave. LIGHTING ENGINEERING

4 Chapter 1. THE LIGHT Wavelength is a highly important characteristic in order to classify the visible radiation spectrum, object of study in this section of LIGHTING ENGINEERING This parameter is determined by the result of propagation velocity ( ), multiplied by the time it takes to cover one cycle (T Period): = (m/s s = m) Frequency ( f ) It is defined as the number of periods that take place in a time unit. Since period is inverse to frequency, = 1, the equation above is transformed into: f = f (m/s 1/s -1 = m) and, therefore, frequency is directly proportional to propagation velocity, and inversely proportional to wavelength. f = (s -1 = cycles/second = Hz) Wavelength decreases when frequency increases. Frequency is stable and independent from the medium through which the wave propagates. This constitutes an important characteristic to classify electromagnetic waves. Propagation velocity ( ) Propagation velocity depends on wave type, elasticity of the medium and rigidity. If the medium is homogeneous and isotropic, propagation velocity is the same in all directions. For example, sound propagation velocity in the air, at 20 ºC, is that of m/s, whereas electromagnetic waves propagation velocity in the vacuum is equivalent to km/s = m/s. The fundamental equation which relates propagation velocity to wavelength and frequency is = f (m s -1 = m/s) 1.3. Frequency spectrum Given the fact that electromagnetic radiations share the same nature and they all propagate in the vacuum at the same velocity ( = m/s), those characteristics that make them different are their wavelength, that is to say, their frequency ( = f). Electromagnetic radiations are the following: gamma rays, X-rays, ultraviolet radiation, light, Infrared rays, microwaves, radio waves and other radiations. The human eye is sensitive to electromagnetic radiation with wavelengths ranging approximately between 380 and 780 nm. This interval is known as visible light. Shortest wavelengths of the visible spectrum correspond to violet light, and the longest, to red light. Between these two extremes are all the colours found in the rainbow (Fig. 2). Electromagnetic waves have slightly shorter wavelengths when compared to visible light and are known as ultraviolet rays. Those with slightly longer wavelengths are known as infrared waves. Thermal radiation emitted by bodies at a normal temperature is placed in the infrared region of the electromagnetic spectrum. There are no limits in electromagnetic radiation wavelength, which is the same as stating that all wavelengths (or frequencies) are possible from a theoretical point of view. It must be taken into account that those wavelength intervals (or frequency ones) in which the electromagnetic spectrum divides sometimes are not well defined and often, they overlap. For example, electromagnetic waves with wavelengths of the order of 0.1 nm. are frequently named X-rays. Nevertheless, if originated from nuclear radioactivity, they are called Gamma rays. 16 LIGHTING ENGINEERING 2002

5 Chapter 1. THE LIGHT Black light 300 nm. 320 Ultraviolet rays 790x10 12 Hz Violet nm. Visible light spectral distribution DSpectral distribution according to lamp manufacturer Indigo Blue Green - Blue Green Green - Yellow Yellow Orange Red 400x10 12 Hz nm nm nm x10 12 Hz 370x10 12 Hz Infrared nm. Figure 2. Classification of visible spectrum. Lamp manufacturers usually give radio spectrometrical curves with values raging between 380 nm. and 780 nm. As we have shown, apart from the meter, nanometer (nm.) is also used in order to express wavelengths, as well as other units like Angstrom (Å) and micron ( m.). 1 m. = m 1 nm. = m 1 Å. = m Radiation of a continuous spectrum source All bodies radiate energy in an ample field of wavelength at any temperature except for absolute zero. This radiation is known as incandescence or temperature radiation. Sources of incandescent artificial light are: -A flame from combustion, like a candle, oil candle, etc. -A red-hot ingot or steal bar. - An incandescent lamp filament, as the most common source to produce artificial light. Incandescence is applied to types of radiation associated with temperature. The spectroradiometer is used to know how the radiated potency is distributed between wavelengths. The spectroradiometrical function or spectral distribution curve obtained is indicated in Fig. 3. Wavelengths in nm. are placed in the abscissas, and values related to energy, with respect to the maximum radiated understood as 100%, are placed in the ordinates. LIGHTING ENGINEERING

6 Chapter 1. THE LIGHT 100 % 100 % Figure 3 Radiation of a discontinuous spectrum source Radiant energy of a gaseous discharge source, such as the ones of high pressure sodium, high pressure mercury, argon, neon, etc., consists in a radiation integrated by small wavelength intervals which may be called emission peaks. Each gas has a wavelength characteristic of its own radiation which depends on the gas molecular structure through which discharge takes place. This kind of discharge is usually called luminescence and it is characterised by temperature independent radiation types. The most common luminous sources or discharge lamps are fluorescent tubes: high pressure mercury, high pressure sodium and induction ones. As for incandescence, the spectroradiometer is used to obtain the spectral distribution curve. The spectroradiometer function obtained is indicated in Fig. 4. Wavelengths in nm. are placed in the abscissas, and values related to energy, with respect to the maximum radiated understood as 100%, are placed in the ordinates. Also, the specific potency in mw/nm.wavelength is usually given in the ordinates. 100 % 100 % nm. 400 nm. 500 nm. 600 nm. 700 nm. 780 nm. 380 nm. 400 nm. 500 nm. 600 nm. 700 nm. 780 nm. 380 nm. 400 nm. 500 nm. 600 nm. 700 nm. 780 nm. 380 nm. 400 nm. 500 nm. 600 nm. 700 nm. 780 nm. Spectral distribution for a normal day light Spectral distribution for an incandescent lamp Spectral distribution for a cold white coloured fluorescent lamp Spectral distribution for a high pressure mercury lamp of corrected colour Figure Dual nature of light Light has intrigued humankind for centuries. The most ancient theories considered light as something emitted by the human eye. Later on, it was understood that light should come from the objects seen and that it entered the eye producing the feeling of vision. The question of whether light is composed by a beam of particles or it is a certain type of wave movement has frequently been studied in the history of science. Between the proponents and defendants of the corpuscular theory of light, the most influential was undoubtedly Newton. Using the above mentioned theory, he was able to explain the laws of reflection and refraction. Nevertheless, his deduction of the law of refraction was based on the hypothesis that light moves more quickly in water or in glass than in air. Some time later, the hypothesis was proved to be wrong. The main proponents of the wave theory of light were Christian Huygens and Robert Hooke. Using 18 LIGHTING ENGINEERING 2002

7 Chapter 1. THE LIGHT their own theory of wave propagation, Huygens was able to explain reflection and refraction supposing that light travels more slowly in glass or in water than in air. Newton realized about the advantages of the wave theory of light, particularly because it explained colours formed by thin films, which he had studied very thoroughly. Notwithstanding, he rejected the wave theory due to the apparent rectilinear propagation of light. In his time, diffraction of the luminous beam, which allows to evade objects, had not yet been observed. Newton's corpuscular theory of light was accepted for more than a century. After some time, in 1801, Thomas Young revitalized the wave theory of light. He was one of the first scientists to introduce the idea of interference as a wave phenomenon present both in the light and in the sound. His observations of interferences obtained from light were a clear demonstration of their wave nature. Nevertheless, Young's research was not known by the scientific community for more than ten years. Probably, the most important breakthrough regarding a general acceptance of the wave theory of light is due to the French physicist Augustin Fresnel ( ), who conducted thorough experiments on interference and diffraction. He also developed a wave theory based on a solid mathematical foundation. In 1850, Jean Foucault measured the speed of light in water and checked that it is slower than in air. Thus, he finally destroyed Newton's corpuscular theory of light. In 1860, James Clerk Maxwell published his electromagnetic mathematical theory which preceded the existence of electromagnetic waves. These waves propagated with a calculated speed through electricity and magnetism laws which was equivalent in value to 3 x 108 m/s, the same value than the speed of light. Maxwell's theory was confirmed by Hertz in 1887 who used a tuned electric circuit to generate waves and another similar circuit to detect them. In the second half of the 19th century, Kirchoff and other scientists applied Maxwell's laws to explain interference and diffraction of light and other electromagnetic waves and support Huygens' empirical methods of wave construction on a solid mathematical basis. Although wave theory is generally correct when propagation of light is described (and of other electromagnetic waves), it fails when other light properties are to be explained, specially the interaction of light with matter. Hertz, in a famous experiment in 1887 confirmed Maxwell's wave theory, and he also discovered the photoelectric effect. Such an effect can also be explained by means of a model of particles for light, as Einstein proved only a few years later. This way, a new corpuscular model of light was introduced. The particles of light are known as photons and energy E of a photon is related to frequency f of the luminous wave associated by Einstein's famous ratio E = h f (h = Planck's constant). A complete understanding of dual nature of light was not achieved before the 20's in the 20th century. Experiments conducted by scientists of the time (Davisson, Germer, Thompson and others) proved that electrons (and other "particles") also had a dual nature and presented interference and diffraction properties besides their well-known particle properties. In brief, the modern theory of quantum mechanics of luminous radiation accepts the fact that light seems to have a dual nature. On the one hand, light propagation phenomena find a better explanation within Maxwell's electromagnetic theory (electromagnetic wave fundamental nature). On the other hand, mutual action between light and matter, in the processes of absorption and emission, is a photoelectric phenomenon (corpuscular nature). LIGHTING ENGINEERING

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9 Chapter 2. THE EYE 2.1. Human eye as a light reception organ Structural description of the eye Image formation Eye sensitivity curve Accommodation Contrast Adaptation Glare LIGHTING ENGINEERING

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11 Chapter 2. THE EYE 2.1. Human eye as a light receptor organ The eye is the physiological organ of sight through which light and colour feelings are experienced. For the lighting process to take place, as action and effect of illuminate and see, three agents are required: 1) A source producing light or luminous radiation. 2) An object to be illuminated so that it is visible. 3) The eye, which receives luminous energy and transforms it into images which are sent to the brain for their interpretation. The study and description of eye components, together with the process which takes place since the moment in which light arrives and goes through the paths and visual centers, until it is interpreted by the brain, would take us to the field of neurophysiology. Some behaviour and concepts related to the sense of sight will be described and exposed in the present chapter. Their knowledge is indispensable and contributes to a better design of lighting installations Structural description of the eye In Fig. 1, a schematic longitudinal section of the human eye is represented, where its anatomic constitution may be observed. Vitreous humor Upper eyelid Aqueous humor Yellow spot Visual axis Ophthalmic muscles Cornea Optical nerve Crystalline lens Iris Ophthalmic muscles Ciliary muscle Retina Lower eyelid Blind spot Sclera Choroids Figure 1. Human eye constitution. The eye is mainly constituted by the following elements: a) Eye globe: whose primary function is to form the image on the retina. b) Cornea: receives and transmits visual impressions and constitutes the eye fundamental optical refractor component. c) Crystaline lens: is a biconvex, transparent and colorless lens located behind the iris. This elastic membrane changes its form to focus objectives. d) Iris: circular lamina located in front of the crystalline lens, and highly pigmented. It can contract the pupil controlling the amount of light that passes to the crystalline lens. e) Pupil: circular orifice situated in the center of the iris, and through which light rays pass. The opening of this orifice is controlled by the iris. Its contraction is called meiosis and its extension, mydriasis. f) Retina: is the eye inner back film constituted by a nervous membrane, expansion of the optical nerve, whose function is to receive and transmit visual images or impressions. It contains an extremely thin layer of photosensitive cells, cones and rods, which diverge from the optical nerve and which are in the external layer, next to the pigmented layer. LIGHTING ENGINEERING

12 Chapter 2. THE EYE g) Cones: photosensitive or photoreceptive cells of the retina which are mainly located in the fovea. They are very sensitive to colours and almost insensitive to light. Hence, their function is to discriminate fine details and to perceive colours (Fig. 2). h) Rods: photosensitive or photoreceptive cells of the retina which are only outside the fovea and more concentrated in the periphery. They are very sensitive to light and movement, and almost insensitive to colour. Thus, their function is to perceive more or less brightness with which objects are illuminated (Fig. 2). i) Macule: yellow spot situated in the rear part of the retina, on the optical axis, where a precise and sharp fixation of details and colours take place. The fovea is in its center which is only formed by cones. j) Blind spot: a spot in the retina through which the optical nerve drives images or feelings of light to the brain. At this point, there are no photoreceptors. Practical consequences of the cone and rod function When we look at a dimly illuminated space, for example, in the twilight at night, visual acuity is low, because cones do not function and neither colours nor details are distinguished. This is the reason for the famous saying "no-one will notice in the dark". This type of night vision is called scotopic and essentially rods intervene, which collect the greater or lesser amount of light and objects movement with extreme sensitivity. This justifies the fact that some public lighting of avenues, roads, and department stores is done with high pressure sodium lamps which reproduce colours badly, but contribute with a great amount of light. On the contrary, with daily light or when illumination level increases the necessary amount, objects are seen with precision and detail also cones, mainly. This way, colours may be distinguished. Daily light is called photopic vision. In this case the quantity requires to be accompanied by quality, since only quantity would produce irritability in eyes and very disturbing glares. Eye globe Nerve cell Pigment grains Rod Retina enlargement Cone Pigmented cell Figure 2. Eye photosensitive part. Behaviour of cones and rods Image formation Human beings visual field is limited by an angle of about 130º degrees in a vertical way and about 180º degrees in a horizontal way. From illuminated objects or those with their own light located in the visual field, luminous rays emerge that go through the cornea and the aqueous humor. The iris, by means of the opening of the pupil, controls the amount of light which is refracted through the crystalline lens to reach the retina finally. In this place, the photosensitive pigment of photoreceptors registers in inverted images much smaller than in reality, as it happens in the photographic camera. Once images are received and formed in the retina by means of the optical nerve, they are sent to the brain, which is in charge of interpreting them and modifying their position (Fig. 3). 24 LIGHTING ENGINEERING 2002

13 Chapter 2. THE EYE Figure 3. Image formation and its rectification in the brain. The following chart compares the human eye to the photographic camera. Human eye Crystalline lens (controls accommodation) Pupil (controls adaptation) Pigment of photoreceptors Retina (creates images) Photographic camera Lens (adjusts distance between lens and film) Diaphragm - shutter (adapts exposition and amount of light) Film emulsion Film (creates images) Chart Eye sensitivity curve Wavelength radiations ranging between 380 nm. (ultraviolet) and 780 nm. (infrared) are transformed by the eye into light. Out of this range, the eye cannot see: it is blind and does not perceive anything. All luminous sources have their own radiation or a mixture of them included within such limits. A sunny midday white light is the sum of all wavelengths of the visible spectrum. If we try to make them reach the eye independently and with the same amount of energy, a curve like the one in Fig. 4 is obtained. It has been elaborated by the C.I.E.* measuring a great number of people. * C.I.E.: International Commission on Illumination (Commission Internationale de l Eclairage). LIGHTING ENGINEERING

14 Chapter 2. THE EYE 100 % Wavelength nm NIGHT DAY 20 0 Figure 4. Eye sensitivity curve to monochromatic radiations. In this curve, the maximum eye sensitivity for day white light (photopic) corresponds to a 555 nm. wavelength and to the yellow colour. The minimum sensitivity corresponds to the red and violet colours. Hence, luminous sources whose wavelength corresponds to yellow - green are the ones with highest efficacy and worst quality, the reason being that such light is not appropriate for our eye, which is accustomed to the sun white light. Thus, in premises where there is a high illumination level orange and red colours are highlighted. In the case of night light (scotopic), the maximum of sensitiveness moves towards shorter wavelengths (Purkinje's effect). Consequently, those radiations with a shorter wavelength (blue- violet) produce greater intensity of sensation with low illumination. Such an effect is very important when illuminating premises with a low illumination level where blue and violet colours can be seen better Accommodation It is the eye capacity to adjust automatically to different distances of objects, and, this way, to obtain sharp images on the retina. This adjustment takes place by modifying the crystalline curvature and, thus, the focus distance by contracting or relaxing ciliary muscles. Provided that the objective is close to the eye, the crystalline curvature is greater than when it is far. In the photographic camera, the lens and the film. Accommodation or focus is easier with high luminances * (lighting) which oblige the pupil to adapt or modify the diaphragm towards a closing position. The common result of this action is the increase of the field depth, or what is the same, a sharp vision of objects at different distances from the eye or camera. The eye accommodation capacity decreases with age, as a result of a hardening of the crystalline Contrast All objects are perceived by contrasts of colour and luminance which different parts of their surface present among themselves and in relation to the background in which the object appears. * Luminance: Luminosity effect which a surface produces on the eye retina, whether it comes from a primary source of light or a reflecting surface. 26 LIGHTING ENGINEERING 2002

15 Chapter 2. THE EYE For high enough lighting levels, the normal eye is colour sensitive, whereas for low lighting ones, objects are fundamentally perceived by luminance contrast which is present against the background. The luminance difference between the observed object and its immediate space is known as contrast. ω L o L f Figure 5 In Fig. 5, the surface of the object has a luminance "L 0 " and the background surface has a luminance "L f ". Therefore, contrast "K" is the difference between these two luminances, divided by their background one, that is to say: K = L 0 L f L f "K" is, thus, a relative value between luminances. As we have commented, the visibility of an object over a background, depends on the luminance difference between the object and the background. For a light coloured object over a dark background, its contrast will be positive (values between 0 and infinitum). However, an object darker than its background will be seen as a silhouette, and its contrast will be negative, varying between 0 and (- 1). Contrast K may be positive or negative: If L 0 > L f K > 0 contrast is positive (the object is lighter than its background). If L 0 < L f K < 0 contrast is negative (the object is darker then its background). Contrast K may acquire the following values: Positive contrast (light object) 0 < K < e Negative contrast (dark object) -1 < K < 0 Example a) in Fig. 6 presents an easily distinguished contrast, whereas b) and c) offer greater difficulty. a b c Figure 6 There is also a colour contrast. Chart 2 shows some examples. LIGHTING ENGINEERING

16 Chapter 2. THE EYE Object colour black green red blue white black yellow white white white Background colour yellow white white white blue white black red green black Chart 2. Colour contrasts. Contrast sensitivity It is a concept derived from the former one which is equivalent to the minimum contrast of luminances that may be perceived by the human eye. Mathematically speaking, it would be the inverse of contrast. L G = f = 1 L 0 L f K Therefore, the greatest sensitivity to contrast possible is approximately: 1 G = = However, in normal practical conditions, sensitivity to contrasts is quite smaller because of the reasons exposed above Adaptation It is the ability of the eye to adjust automatically to different lighting degrees for objects. It consists of the adjustment of the size of the pupil so that luminance projected in the retina is equal to a value bearable by sensitive cells. If compared to a photographic camera, it would be the greater or lesser opening of the diaphragm. If lighting is very intense, the pupil contracts, decreasing the amount of light that reaches the crystalline. If lighting is scarce, it expands to capture more of it. In high value illuminations, the pupil reduces to a diameter of approximately 2 mm. In very low value illuminations, the pupil expands up to about 8 mm. When a person moves from a place with high illuminance to another which is completely dark, the eye undergoes an adaptation process. In order to adjust totally to the new situation, the eye needs 30 minutes. The opposite process, when a person goes from a completely dark place into another with high illuminance, the adaptation period lasts for only a few seconds (Fig. 7). 28 LIGHTING ENGINEERING 2002

17 θ Chapter 2. THE EYE Relative photosensitivity 100 % Adaptation time (min.) Figure 7. Eye relative photosensitive curve regarding adaptation time Glare It is a phenomenon that produces disturbance or decrease in the capacity to distinguish objects, or else, both things at the same time. This could be due either to an inadequate luminance distribution or phasing or to excessive contrasts in space or time. This phenomenon affects the retina of the eye: an energetic photochemical reaction is produced which desensitizes it for a certain period of time, after which, it recovers. Effects produced by glare may be classified as psychological (discomfort) or physiological (disability). It may be produced in different ways: direct glare, like the one from sources of light (lamps, luminaires or windows), which are located within the field of vision. Reflected glare specially from surfaces with great reflectance, specular surfaces like polished metal. Sources of light generally give rise to a disability glare which is proportional to the lighting produced by the source of light on the eye pupil, as well as to a factor dependent on the q angle. Such an angle is formed by both the straight line R which joins the eye with the F focus and the H horizontal plane which goes through the eye in a working position. In Fig. 8, different glares are indicated, depending on the angle function. A minimum value of 30 has been taken as admissible. Glare R H F Values for the angle Figure 8. Glare according to the q angle. LIGHTING ENGINEERING

18 Chapter 2. THE EYE Surfaces which are not completely matte give rise to more or less sharp images of their sources of light due to light reflection. Even if their luminance is not excessive, such images are almost always discomforting when found in the field of vision, and specially, in its central area. According to these lines, all unnecessary polished surfaces will be avoided as far as possible (glass over tables, for example.). In case semipolished surfaces are used (blackboards), sources of light will have the least possible luminance and their position will be calculated bearing in mind reflexes that may occur (filters, grids, diffusers, etc.). In special cases, images which provide reflection will be useful (silhouette effect vision, flaw inspection in polished surfaces, typesetting, etc.). Figure 9. Surfaces which reflect light. 30 LIGHTING ENGINEERING 2002

19 Chapter 3. MATTER OPTICAL PROPERTIES 3.1. General remarks Reflection Transmmission Absorption Refraction LIGHTING ENGINEERING

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21 Chapter 3. MATTER OPTICAL PROPERTIES 3.1. General remarks When a light ray propagates along a medium and reaches the limit which separates it from the second one, it may return to it (reflection), it may strike it and become part of the second medium, where it will be converted into a different form of energy (absorption), and some will not change (transmission). Out of these phenomena, two or three take place simultaneously. Following the fundamental principle of energy, the sum of reflected, absorbed and transmitted radiation must equal the incident radiation. Therefore, the use of light in the most convenient way requires control and distribution achieved by modifying its characteristics through the physical phenomena of light reflection, absorption and transmission, without leaving aside the fourth factor known as refraction Reflection When any type of waves strikes a flat surface like a mirror, for example, new waves that move away from the surface are generated. This phenomenon is known as reflection. When light is returned by a surface, a certain amount of light is lost due to the absorption phenomenon. The ratio between the reflected flux and the incident flux is called surface reflectance Any surface which is not completely dark may reflect light. The amount of reflected light is determined by the surface reflection properties. There are four kinds of reflection, namely: specular, composed, diffused and mixed. Reflector systems are based on these reflection properties. Specular reflection (Fig. 1): It takes place when the reflecting surface is flat. This kind of reflection is based on two fundamental laws: 1. The incident ray, the reflected ray and the normal to the surface at the point of incidence lie in the same plane. 2. The angle of incidence (i) is the same as the angle of reflection (r). N i r Figure 1. Specular reflection. Composed reflection (Fig. 2): Contrary to specular reflection, there is no mirror image of the light source, but the maximum angle of reflected intensity is the same as the angle of incidence. This type of reflection takes place when the surface is irregular or rough. LIGHTING ENGINEERING

22 Chapter 3. MATTER OPTICAL PROPERTIES Figure 2. Composed reflection. Diffused reflection (Fig. 3): This takes place when the light that strikes a surface is reflected in all directions, the normal ray to the surface being the most intense one. This kind of reflection takes place on surfaces such as matt white paper, walls, plaster flat ceilings, snow, etc. Figure 3. Diffused reflection. Mixed reflection (Fig. 4): This is an intermediate kind of reflection between the specular and the diffused reflection, in which some of the incident beam is reflected and some, diffused. This kind of reflection takes place with non polished metals, glossy paper and barnished surfaces. Figure 4. Mixed reflection. 34 LIGHTING ENGINEERING 2002

23 Chapter 3. MATTER OPTICAL PROPERTIES Reflecting surface % reflection index Gloss silver Gold Matte silver Polished nickel Polished chrome Polished aluminium Electropolished aluminium Vaporised aluminium Copper Iron Enamelled porcelain Mirrors Matte white paint Light beige Yellow and light cream Accoustic ceilings Light green Light green and pink Light blue Light grey Light red Light brown Dark beige Dark brown, green and blue 5-20 Black 3-4 Chart 1. Reflection coefficient for white daylight Transmmission Radiation passes through a medium without a change in the frequency of monochromatic radiations. This phenomenon can be seen on certain kinds of glass, crystal, water and other liquids, and air, of course. However, when passing through the material, some of the light is lost due to the reflection on the medium surface and through absorption. The relation between the transmitted light and the incident light is known as material transmittance. Transmission falls into three categories: spread, diffused and mixed. Spread transmission (Fig. 5): The beam strikes a medium and passes through it. The media which fulfill this property are called transparent materials and allow a sharp view of objects on the opposite side. LIGHTING ENGINEERING

24 Chapter 3. MATTER OPTICAL PROPERTIES Figure 5. Spread transmission. Diffused transmission (Fig. 6): The incident beam spreads through the medium, coming out of it in scattered directions. These transmitting media are called translucent. The most common ones are ground glass and opalized organic glass. Objects situated behind them appear blurred. Figure 6. Diffused transmission. Mixed transmission (Fig. 7): This is a kind of combination between spread and diffused transmission. It is produced with organic, polished and carved surface glass. Although beam spread is not complete, objects situated behind them appear blurred, but their position is relative. Figure 7. Mixed transmission. 36 LIGHTING ENGINEERING 2002

25 Chapter 3. MATTER OPTICAL PROPERTIES 3.4. Absorption Process by which radiant energy is converted into a different form of energy, mainly in the form of heat. This phenomenon is characteristic both of all surfaces which are not completely reflective and of materials which are not totally transparent. The ratio between absorbed flux to incident flux is known as absorptance. Absorption of certain light wavelengths is called selective absorption. Generally speaking, objects take their color from selective absorption Refraction The direction of the light beam may change when passing from one medium to the other. This is a result of a change in the light speed of propagation. Speed decreases if the new media density is higher, and increases if it is lower. This change in speed and direction is known as refraction. There are two laws of refraction: 1. When the wave goes from one medium to another, the incident ray, the reflected ray and the normal to the separating surface of the media on the incidence point, are on the same plane. 2. The ratio between the incidence angle sine and the refraction angle sine is a constant for the given pair of media. The above mentioned constant is known as the index of refraction n, for the given media. The second law of refraction is usually known as Snell s law. α 1 n 1 n 2 α 2 n 1 α 1 D Figure 8. Refraction in the boundary bewtween two media. n 1 * = angle of refration for the first medium. n 2 * = angle of refraction for the second medium. a 1 = angle of incidence. a 2 = angle of refraction. When the first medium is the air, n 1 = 1 and the formula is: n 1 sin a 1 = n 2 sin a 2 c sin a1 = n2 = n sin a 2 = n 1 sin a 1 = n 2 sin a 2 The distance D in figure 8 is known as displacement. Such a displacemnt depends on the angle of incidence and on the index of refraction. When the incident ray is perpendicular to the surface, refraction and displacement equal zero. LIGHTING ENGINEERING

26 Chapter 3. MATTER OPTICAL PROPERTIES Refraction varies according to wavelength. Short waves (like blue and violet) are transmitted better than long waves (for example red). This phenomenon is used to decompose white light into its component colours when passing through a refraction prism. The degree to which color is decomposed depends on the angle of incidence and the refraction properties of the prism material. This is called dispersion. * n i is calculated by the quotient between the speed of light in the air and the speed of light in the medium i. 38 LIGHTING ENGINEERING 2002

27 Chapter 4. THE COLOUR 4.1. General remarks Colour classification according to the C.I.E. chromatic diagram Colour temperature (T c ) Colour rendering index (R) Colour and harmony psychic effects LIGHTING ENGINEERING

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29 Chapter 4. THE COLOUR 4.1. General remarks Colour is a subjective psycho physiologic interpretation of the visible electromagnetic spectrum. Luminous sensations or images, produced in our retina, are sent to the brain and interpreted as a set of monochromatic sensations which constitute the colour of the light. The sense of sight does not analyze each radiation or chromatic sensation individually. For each radiation there is a colour designation, according to the frequency spectrum classification. It is important to indicate that objects are distinguished by the colour assigned depending on their optical properties. Objects neither have nor produce colour. They do have optical properties to reflect, refract and absorb colours of the light they receive, that is to say: the set of additive monochromatic sensations that our brain interprets as colour of an object depends on the spectral composition of the light that illuminates such an object and on the optical properties possessed by the object to reflect, refract or absorb. Newton was the first one to discover the decomposition of white light in the group of colours that forms a rainbow. When a white light beam went through a prism, the same effect as that indicated in Fig. 1 was obtained. Prism 380 nm. 400 nm. White light 500 nm. 600 nm. 700 nm. 780 nm. Figure 1. White light decomposition in the rainbow spectrum Colour classification according to the C.I.E. chromatic diagram Subjective evaluations of object surfaces, in the same way they are perceived by the human eye, are interpreted bearing in mind colour attributes or qualities. They are the following: a) Lightness or brightness: Luminous radiation received according to the illuminance possessed by the object. The further from black in the grey scale, the lighter the colour of an object. It refers to intensity. b) Hue or tone: common name for colour (red, yellow, green, etc.). It refers to wavelength. c) Purity or saturation: proportion in which a colour is mixed with white. It refers to spectral purity. In order to avoid a subjective evaluation of colour there exists a chromaticity diagram in the shape of a triangle, approved by the C.I.E. It is used to treat sources of light, coloured surfaces, paints, luminous filters, etc. from a quantitative point of view. All colours are ordered following three chromatic coordinates, x, y, z, whose sum is always equivalent to the unit (x + y + z = 1). When each of them equals 0.333, they correspond to the white colour. These three coordinates are obtained from the specific potencies for each wavelength. It is based on the fact that when three radiations from three sources of different spectral composition are mixed, a radiation equivalent to another with a different value may be obtained. The result is the triangle in Fig. 2, in which any two coordinates are enough to determine the radiation colour resulting formed by the additive mixture of three components. LIGHTING ENGINEERING

30 Chapter 4. THE COLOUR Figure 2. C.I.E. Chromaticity diagram 4.3. Colour temperature (T C ) In the C.I.E. chromaticity diagram in Fig. 2, a curve has been drawn representing the colour emitted by a black body according to its temperature. It is known as black body colour temperature curve, T C.. Colour temperature is an expression used to indicate the colour of a source of light by comparing it with a black body colour, that is to say, a "theoretical perfect radiant" (object whose light emission is only due to its temperature). As any other incandescent body, the black body changes its colour as its temperature increases, acquiring at the beginning, a red matte tone, to change to light red later on, orange, yellow and finally white, bluish white and blue. For example, colour of a candle flame is similar to the one of a black body heated at about K*. Then, the flame is said to have a "colour temperature" of K. Incandescent lamps have a colour temperature which ranges from to K, depending on their type. Their fleck is determined by the corresponding coordinates and is located virtually on the black body curve. Such temperature bears no relation at all with that of an incandescent filament. Therefore, colour temperature is, in fact, a measure of temperature. It only defines colour and it can be applied exclusively to sources of light which have a great colour resemblance with the black body. The practical equivalence between colour appearance and colour temperature is established arbitrarily according to Chart 1. * K = Kelvin. Temperatures of Kelvin s scale exceed in 273 C the corresponding ones in the centigrade scale. 42 LIGHTING ENGINEERING 2002

31 Chapter 4. THE COLOUR Colour appearance group Colour appearance Colour temperature (K) 1 Warm Below Intermediate From to Cold Above Chart Colour rendering index (R) Colour temperature datum is only referred to the colour of light, but not to its spectral composition which is decisive for colour reproduction. Thus, two sources of light may have a very similar colour and possesses, at the same time, very different chromatic reproduction properties. The colour rendering index (R) characterizes the chromatic reproduction capacity of objects illuminated with a source of light. The R offers an indication of the capacity of the source of light to reproduce normalized colours, in comparison with the reproduction provided by a light as reference pattern. Luminous sources Tc ( K) R.C. Blue sky a to 100 (group 1) Cloudy sky to 100 (group 1) Daylight to 100 (group 1) Discharge lamps (except for Na) Daylight (halogene) to 100 (group 1) Neutral white a to 84 (group 2) Warm white Lower than to 69 (group 3) Discharge lamp (Na) Lower than 40 Incandescent lamp a to 100 (group 1) Photographic lamp to 100 (group 1) Candle flame or oil candle to 69 (group 3) Chart 2 LIGHTING ENGINEERING

32 Chapter 4. THE COLOUR Lamps colour rendering groups In order to simplify the specifications for lamp colour rendering indexes of those used in lighting, colour rendering groups have been introduced as indicated in Chart 3. Rendering group Rendering range in Colour appearance Examples for preferible uses Examples for acceptable use in colour colour (R or R a ) Warm 1 A R 90 Intermediate Cold Warm 1 B 90 > R 80 Intermediate Intermediate Warm Colour equalness, medical explorations, art galleries Houses, hotels, restaurants, shops, offices, schools, hospitals Printing, painting and textile industry, industrial work Warm 2 80 > R 60 Intermediate Industrial work Offices, schools Cold 3 60 > R 40 Rough industries Industrial work Rough work, industrial work 4 40 > R 20 with low requisites for colour rendering Chart 3. Lamp colour rendering groups Colours and harmony psychic effects It has been proved that colour in the environment produces psychic or emotional reactions in the observer. Hence, using colours in the adequate way is a very relevant topic for psychologists, architects, lighting engineers and decorators. There are no fixed rules for choosing the appropriate colour in order to achieve a certain effect, since each case requires to be given a particular approach. However, there are some experiences in which different sensations are produced in the individual by certain colours. One of the first sensations is that of heat or coldness. This is the reason why the expression "hot colours" and "cold colours" is mentioned. Hot colours are those which go from red to greenish yellow in the visible spectrum; cold colours the ones from green to blue. A colour will be hotter or colder depending on its tendency towards red or blue, respectively. On the one hand, hot colours are dynamic, exciting and produce a sensation of proximity. On the other hand, cold colours calm and rest, producing a sensation of distance. Likewise, colour clarity also produces psychological effects. Light colours cheer up and give a sensation of lightness, while dark colours depress and produce a sensation of heaviness. When two or more colours are combined and produce a comfortable effect, it is said that they harmonize. Thus, colour harmony is produced by means of selecting a colour combination which is comfortable and even pleasant for the observer in a given situation. From all the above mentioned, it may be deduced that a knowledge of the spectral distribution curve of sources of light is necessary to obtain the desired chromatic effect. 44 LIGHTING ENGINEERING 2002

33 Chapter 5. LUMINOUS MEASUREMENTS 5.1. Luminous flux (luminous output) Amount of light (luminous energy) Luminous intensity Illuminance (luminous level) Luminance Other interesting luminous measurements Luminous measurement graphic representation Luminous measurement summary chart LIGHTING ENGINEERING

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35 Chapter 5. LUMINOUS MEASUREMENTS Two basic elements intervene in lighting engineering: both the source of light and the object to be illuminated. In the present chapter, we will deal with fundamental measurements and units used to evaluate and compare the quality and effects of sources of light Luminous flux (luminous output) Energy transformed by light sources cannot be totally taken advantage of for light production. For example, an incadescent lamp consumes a certain amount of electric energy which is transformed into radiant energy. Out of this, only a small amount (about 10%) is perceived by the human eye as light, while the rest of it is lost as heat. A luminous flux produced by a source of light is the total amount of light, either emitted or radiated in all directions in one second. More precisely, a source of light luminous flux is radiated energy received by the human eye depending on its sensitivity curve, and which is transformed into light for a second. Luminous flux is represented by the Greek letter F and is measured in lumens (lm). Lumen is the luminous flux of the monochromatic radiation characterised by a value frequency of Hz. and a radiant power flux of 1/683 W. One 555 nm. wavelength radiant energy watt in the air equals 683 lm approximately. Luminous flux measurement Luminous flux measurement is conducted by means of an adjusted photoelement depending on the phototopic sensitivity curve of the standard eye to the monochromatic radiations, incorporated to a hollow sphere known as Ullbricht s sphere (Fig. 1). The source to be measured is placed inside it. Manufacturers provide lamp flux in lumens for nominal potency. Figure 1. Ullbricht s sphere. Luminous performance (Luminous efficacy) Luminous performance of a source of light indicates the flux emitted by this source per unit of electrical output consumed to obtain it. It is represented by the Greek letter e, and it is measured as lumen/watt (lm/w). The formula which expresses luminous efficacy is: ε = Φ Ρ (lm/w) If a lamp was to be manufactured which transformed all the consumed electrical output into light at one 555 nm. wavelength without losses, such a lamp would have the highest performance possible. Its value would be 683 lm/w. LIGHTING ENGINEERING

36 Chapter 5. LUMINOUS MEASUREMENTS 5.2. Amount of light (Luminous energy) In a similar way to electrical energy, which is determined by the electrical output in the time unit, the amount of light or luminous energy is determined by the luminous output or luminous flux emitted by the time unit. The amount of light is represented by the letter Q, and is measured as lumen per hour (lm h). The formula which expresses the amount of light is the following: Q = F t (lm h) 5.3. Luminous intensity This measurement is solely understood as referred to a specific direction and contained in a w solid angle. In the same way that a plane angle measured in radians corresponds to a surface, a solid or stereo angle corresponds to a volume measurement and is measured in stereoradians. The radian is defined as the plane angle within an arc of a circle, equal to the radius of the circle. (Fig. 2). δ = 1 α = 1 radian r = 1 α (total) = 2 π radians Figure 2. Plane angle. The stereoradian is defined as the solid angle which corresponds to a spherical cap whose surface equals the square of the sphere radius (Fig. 3). 1cd r = 1m. ω φ = 1 Lm E = 1 Lux S = 1 m 2 1cd ω (total) = 4π stereoradians Figure 3. Solid angle. Luminous output of a source of light in one specific direction equals the ratio between the luminous flux contained in whatever solid angle whose axis coincides with the considered direction. Its symbol is, and its unit of measurement is the candela (cd). The formula which expresses it is the following: Ι = Φ ω (lm/sr) Candela is defined as the luminous intensity of a specific source which emits luminous flux equal to one lumen in a solid angle per stereoradian (sr). 48 LIGHTING ENGINEERING 2002

37 Chapter 5. LUMINOUS MEASUREMENTS According to the I.S.*, candela may also be defined as the luminous intensity in a certain direction, from a source which emits monochromatic radiation with a frequency of Hz, and whose energy intensity in the aforementioned direction is 1/683 watts per stereoradian Illuminance (Luminous level) Illuminance or luminous level of a surface is the ratio between the luminous flux received by the surface to its area. It is represented by the letter E, and its unit is the lux (lx). The formula which expresses illuminance is: Ε = Φ S (lx = lm/m 2 ) Thus, according to the formula, the higher the luminous flux incident on a surface, the higher its illuminance. Also, for the same given incident luminous flux, illuminance will be higher as surface decreases. According to the I.S., lux may be defined as the illuminance of a certain surface which receives a luminous flux of one lumen, spread over one square meter of its surface. Lighting level measurement Luminous level measurement is conducted with a special device known as foot- candle metre. It consists of one photoelectric cell which generates a weak eletric current when light strikes its surface, thus, increasing according to light incidence. Such current is measured by means of an analogic or digital miliammeter, calibrated directly in lux (Fig. 4). A B Figure 4. Foot- candle metre Luminance Luminance is the effect which produces a surface on the retina of the eye, both coming from a primary source which produces light, or from a secondary source or surface which reflects light. Luminance measures brightness for primary light sources as well as for sources constituting illuminated objects. This term has substituted the concepts of brightness and lighting density. Nevertheless, it is interesting to remember that the human eye does not perceive colours but brightness, as a colour attribute. Light perception is, in fact, the perception of differences in luminance. Therefore, it may be stated that the eye perceives luminance differences but not illuminance ones (provided that we have the same lighting, different objects have different luminance since they have different reflection characteristics). Luminance of an illuminated surface is the ratio between luminance of a source of light in a given direction, to the surface of the projected source depending on such direction. *I.S.c International System. LIGHTING ENGINEERING

38 Chapter 5. LUMINOUS MEASUREMENTS Viewed or apparent surface β Apparent surface = Real surface x cosβ β β Real surface Figure 5. Surface luminance. The projected area is seen by the observer in the direction of the luminous intensity. This area is calculated by multiplying the illuminated real surface by the cosine angle forming the normal with the direction of the luminous intensity (Fig. 5). Represented by the letter L, its unit is the candela/square metre called nit (nt), with one submultiple, the candela/square centimetre or stilb, used for high luminance sources. The formula which expresses it is the following: 1nt = 1cd 1m 2 where: S cos = Apparent surface. Luminance is independent from the observation distance. ; Ι L = S cosβ 1stilb = 1cd 1cm 2 Luminance measurement Luminance measurement is conducted by means of a special device called a luminancemetre or nitmeter. It is based on two optical systems, directional and measurement systems, respectively. (Fig. 6). The directional system is oriented in such a way that the image coincides with the point to be measured. Once it has been oriented, the light that reaches it is transformed into electric current. Its values are measured in cd/m Figure 6. Luminancemeter. 50 LIGHTING ENGINEERING 2002

39 Chapter 5. LUMINOUS MEASUREMENTS 5.6. Other interesting luminous measurements Utilization coefficient Ratio between the luminous flux received by a body and the flux emitted by a source of light. Unit c % Symbol c η Ratio c η = Φ Φ e Reflectance Ratio between the flux reflected by a body (with or without diffusion) and the flux received. Unit c % Symbol c ρ Ratio c ρ = Φ r Φ Absorptance Ratio between the luminous flux absorbed by a body and the flux received. Unit c % Symbol c α Ratio c α = Φ a Φ Transmittance Ratio between the luminous flux transmitted by a body and the flux received. Unit c % Symbol c τ Ratio c τ = Φ t Φ Average uniformity factor Ratio between minimum to medium illuminance in a lighting installation. Unit c % Symbol c U m Ratio c U m = Ε min Ε med Extreme uniformity factor Ratio between minimum to maximum illuminance in a lighting installation. Unit c % Symbol c U e Ratio c U e = Ε min Ε max Longitudinal uniformity factor Ratio between longitudinal minimum to maximum luminance in a lighting installation. Unit c % Symbol c U L Ratio c U L = L longitudinal min L longitudinal max Overall luminance uniformity Ratio between minimum to medium illuminance in a lighting installation. Unit c % Symbol c U 0 Ratio c U 0 = L min L med LIGHTING ENGINEERING

40 Chapter 5. LUMINOUS MEASUREMENTS Maintenance factor Coefficient indicating the preservation degree of an installation. Unit c % Symbol c F m Ratio c F m = F pl F dl F t F e F c F pl F dl F t F e F c = lamp position factor = lamp depreciation factor = temperature factor = ignition equipment factor = installation preservation factor 5.7. Luminous measurement graphic representation The collection of luminous intensity emitted by a source of light in all directions is known as luminous distribution. The sources of light used in practice have a more or less large luminous surface, whose radiation intensity is affected by the construction of the source itself, presenting various values in these scattered directions. Special devices (like the Goniophotometer) are constructed to determine the luminous intensity of a source of light in all spatial directions in relation to a vertical axis. If luminous intensity (I) of a source of light is represented by vectors in the infinite spatial directions, a volume representing the value for the total flux emitted by the source is created. Such a value may be defined by the formula below: r r Φ =! Ι dω ν Photometric solid is the solid obtained. Fig. 7 shows an incasdescent lamp photometric solid Figure 7. Incandescent lamp photometric solid. If a plane passes through the symmetric axis of a source of light, for example, a meridional plane, a section limited by a curve, known as photometric curve, or luminous distribution curve is obtained (Fig. 8). 52 LIGHTING ENGINEERING 2002

41 Chapter 5. LUMINOUS MEASUREMENTS cd Figure 8. Photometric curve for an incandescent lamp. By reviewing the photometric curve of a source of light, luminous intensity in any direction may be determined very accurately. This data are necessary for some lighting calculations. Therefore, spatial directions through which luminous radiation is irradiated may be established by two coordinates. One of the most frequently used coordinate systems to obtain photometric curves is the C - represented in Fig. 9. C = 180 rotation axis "C" planes C = 90 C = 270 inclination axis C = 0 γ = 180 γ = 90 γ = 0 Roadway side Walkway side Figure 9. C - coordinate system. Photometric curves refer to an emitted luminous flux of lm. Generally speaking, the source of light emits a larger flux. Thus, the corresponding luminous intensity values are calculated by a simple ratio. When a lamp is housed in a reflector, its flux is distorted, producing a volume with a marked shape defined by the characteristics of the reflector. Therefore, distribution curves vary according to different planes. The two following figures show two examples where distribution curves for two reflectors are represented. Fig.10 reflector is symmetric and has identical curves for any of the meridional planes. This is LIGHTING ENGINEERING

42 Chapter 5. LUMINOUS MEASUREMENTS the reason why a sole curve is enough for its photometric identification. Fig. 11 reflector is asymmetric and each plane has a different curve. All planes must be known o 30 o 0 o 30 o Unit = cd/1000 lm C=90º C=45º C=0º Figure 10. Symmetric photometric distribution curve o 50 o 30 o 10 o 0 o Unit = cd/1000 lm C=90º C=45º C=0º Figure 11. Asymmetric photometric distribution curve. Another method to represent luminous flux distribution is the isocandela curve diagram (Fig. 12). According to this diagram, luminaires are supposed to be in the center of a sphere where exterior surface points with the same intensity are linked (isocandela curves). Generally, luminaires have, at least, one symmetric plane. This is the reason why they are only represented in a hemisphere C= GM= Imax=100% Figure 12. Isocandela curves. 54 LIGHTING ENGINEERING 2002

43 Chapter 5. LUMINOUS MEASUREMENTS This representation is very comprehensive. However, more experience is needed to interpret it. The flux emitted by a source of light provides surface lighting (illuminance) whose values are measured in lux. If those values are projected on the same plane and a line links the ones with the same value, isolux curves are formed (Fig. 13). h WALKWAY SIDE h h ROADWAY SIDE 3h 6h 5h 4h Lmax=100% fl= h 2h h 0 h 2h 3h Figure 13. Isolux curves. Finally, luminance depends on the luminous flux reflected by a surface in the observer s direction. Values are measured in candelas per square metre (cd/m 2 ) and are represented by isoluminance curves (Fig. 14). OBSERVERS: A, B AND C A B h 6h 5h 4h ROADWAY SIDE 3h 2h h 0 h 2h 3h C h 10 2h 3h WALKWAY SIDE Roadway R2 Qo = 0.07 Lmax=100% fl= Figure 14. Isoluminance curves. LIGHTING ENGINEERING

44 Chapter 5. LUMINOUS MEASUREMENTS 5.8. Luminous measurement summary chart Measurement Symbol Unit Ratio Luminous flux F Lumen (lm) F = I q Luminous efficacy ε Lumen per watt (lm/w) ε = Φ Ρ Luminous output Q Lumen per hour (lm h) Q = F t Candela (cd) Luminous intensity Ι Ι = Φ (cd = lm/sr) ω Lux (lx) Illuminance Ε Ε = Φ (lx = lm/m 2 ) S Nit = cd/ m 2 Luminance L L = Stilb = cd/cm 2 Ι S cosβ Utilization coefficient η % η = Φ Φ e Reflectance ρ % ρ = Φ r Absorptance α % α = Φ a Transmittance τ % τ = Φ t Average uniformity factor U m % U m = Ε min Extreme uniformity factor U e % U e = Ε min Longitudinal luminance uniformity U L % U L = L longitudinal min L longitudinal max Overall luminance uniformity U 0 % U 0 = L min Φ Φ Φ Ε med Ε max L med Maintenance factor F m % F m = F pl F dl F t F e F c Chart 1. Luminous measurement summary 56 LIGHTING ENGINEERING 2002

45 Chapter 6. FUNDAMENTAL PRINCIPLES 6.1. Inverse square distance law Cosine law Normal, horizontal, vertical and inclined planes illumination Illuminance ratio Lambert s law LIGHTING ENGINEERING

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47 Chapter 6. FUNDAMENTAL PRINCIPLES 6.1. Inverse square distance law Since early experiments, it has been confirmed that illuminances produced by the source of light decrease inversely to the square of the distance from the plane to illuminate the source. This ratio is expressed by the following formula: Ε = Ι d 2 (lx) where Ε is the illuminance level in lux (lx), Ι is the intensity of the source in candelas (cd), and d is the distance from the source of light to the perpendicular receptor plane. In this way, an illuminance ratio Ε 1 and Ε 2 may be established, between two planes separated by a distance d and D from the source of light, respectively: Ε 1 d 2 = Ε 2 D 2 Ε 1 D 2 = Ε 2 = d 2 S2 S1 E2 F E1 d D Figure 1. Luminous flux distribution over different surfaces. This law is fulfilled when we are dealing with a punctual source of perpendicular surfaces to the direction of the luminous flux. However, the law is supposed to be accurate enough when the distance undergoing measurement is, at least, five times the maximum dimension of the luminaire (the distance is big in relation to the size of the area of the source of light) Cosine law In the previous section, the surface was perpendicular to the direction of luminous rays, but when a specific angle a is formed in relation to this, the formula for the inverse square distance law must be multiplied by the cosine of the corresponding angle. Such an expression constitutes what is called the law of cosine, expressed in the formula below: Ε = Ι cos α (lx) d 2 LIGHTING ENGINEERING

48 Chapter 6. FUNDAMENTAL PRINCIPLES Illuminance in any given point of a surface is proportional to the cosine of the angle of incidence of the luminous rays in the illuminated point. In Fig. 2 two sources of light F and F with the same luminous intensity (I) and at the same distance (d) from point P are represented. To the source of light F with cos0 = 1 corresponds an angle of incidence equal to zero. This source produces illuminance for the point P with a value of: h F' d α 60 P F d Figure 2. Iluminance at a point from two sources of light with different angles of incidence. Ε p = Ι cos 0 = Ι 1 d 2 d 2 c Ε p = Ι (lx) d 2 Likewise, F with an angle α = 60, corresponding cos60 = 0.5, will produce at the same point an illuminance valued as: Ε ṕ = Ι cos 60 = Ι 0.5 d 2 d 2 c Ε ṕ = 1 Ι 2 d 2 (lx) Therefore, Ε ṕ = 0.5 Ε p, that is to say, to obtain the same illuminance at point P, the luminous intensity of the source F must double that of the source F. In practice, distance d from the source to the considered point is not known, but its height h to the horizontal of the point is. By using a simple trigonometric relation and substituing it in the equation, a new relation where height h plays an important role is obtained: cos α = h c d = h d cos α Ε p = Ι cos α = d 2 ( Ι h cos α ) 2 cos α = Ι h 2 cos 2 α cos α Ε p = Ι cos 3 α (lx) h 2 60 LIGHTING ENGINEERING 2002

49 Chapter 6. FUNDAMENTAL PRINCIPLES 6.3. Normal, horizontal, vertical and inclined planes illumination In Fig. 3 the source F illuminates three planes situated in the following positions: normal, horizontal and vertical to the beam. Each will have an illuminance called: E N = Normal illuminance. E H = Horizontal illuminance. E V = Vertical illuminance. F M2 α Iα d Vertical illuminance h β Normal illuminance M1 M Horizontal illuminance a Figure 3. Normal, horizontal and vertical illuminance. Let us determine the normal, horizontal and vertical illuminance for point M in Fig. 3. Normal illumination The inverse square distance law is applied: Ε N = Ι α d 2 (lx) where Iα is the luminous intensity under the angle a. Virtually, only normal illuminance of a point is considered whenever this point is situated in the vertical of the source on the horizontal plane (M 1 point). Thus, the previous formula is transformed into: Ε N = Ι (lx) h 2 and also when it is situated in a straight line with the source on the vertical plane (M 2 point), the illuminance is: Ε N = Ι (lx) a 2 Horizontal illumination If the law of cosine is directly applied, the result is: Ε H = Ε N cos α = Ι α cos α (lx) d 2 Such a formula may be reformulated in relation to the height h between the F source and the M point (d = h / cosα): Ε H = Ι α cos3 α (lx) h 2 LIGHTING ENGINEERING

50 Chapter 6. FUNDAMENTAL PRINCIPLES Vertical illumination In this case, the law of the cosine is also directly applied. The result is that: Ε V = Ε N cos β (lx) Between the α and β angles, there is a simple relation since both belong to a triangle rectangle. α + β + 90 = 180 c β = 90 - α Applying trigonometric relations: cosβ = cos(90 - α) = cos90 cosα + sin90 sinα Therefore, cosβ = sinα. This value is substituted and the result is that: Ε V = Ε N sin α (lx) Ε V = Ι α sin α (lx) d 2 The equation may be expressed in relation to the height h between the F source and the M point. Ε V = Ι α cos2 α sin α (lx) h 2 Inclined planes illumination The vertical plane may change through an angle like the one in Fig. 4. Such an angle forms the vertical plane which contains the point P with the light incidence plane. h α I γ P Figure 4. Illuminance at point P. Taking this into account, the above mentioned expression is transformed into: Ε PI = Ι α cos2 α sin α cos γ (lx) h 2 h is the vertical height of the source of light over the horizontal plane which contains point P Illuminance ratio Different concepts to describe light coming from other directions different from the vertical have been proposed. These must be considered as comfort parameters together with others like luminous level (illuminance). Vertical / horizontal The experience from high illuminance level installations with a very good glare control indicates that the ratio between vertical (E V ) and horizontal illuminance (E H ) for a good modelling* must not be lower than 0.25 in the main directions of vision. Ε V 0.25 Ε H * Modelling: Ability of light to reveal the texture and tridimensional form of an object creating light and shade contrasts. 62 LIGHTING ENGINEERING 2002

51 Chapter 6. FUNDAMENTAL PRINCIPLES Vectorial /Spherical Directional lighting effects may be described partly through vectorial illuminance and partly through the ratio between vectorial and spherical illuminance. The illuminance vector Ε at a point has a magnitude equal to the maximum difference in illuminance over those diametrically opposed surface elements in a small disc (Fig. 5) located in a point, their direction being from the greatest illuminance element to the lowest one. Ef E Er Figure 5. Illuminance vector E = Ef Er. The spherical average at point is the average illuminance over all the surface of a small sphere located at such a point (Fig. 6). Es Figure 6. Spherical medium illuminance E S. Lighting directional intensity may be indicated by the given modelling through the ratio between vectorial illuminance and average spherical illuminance: Ε Ε S If we measure it using a sphere with a radius r which receives a beam of light with an F luminous flux, it would be: Φ Ε S = 4 π r 2 Illuminance E of an element of the radius r surface is: Ε = Φ π r 2 In a room with a floor, walls and a flat ceiling with diffused reflection, where there is also diffused light, we have that j Ε j 0 (that is to say, there are no shadows). Under these circumstances, the modelling index is j Ε /Ε s j 0. However, in a completely dark room where LIGHTING ENGINEERING

52 Chapter 6. FUNDAMENTAL PRINCIPLES the light comes from one direction only (for example, sunlight), j Ε = Ε (that is to say, dark shadows). Under these circumstances, the modelling index is equivalent to j Ε /Ε= Ε / Ε s = 4. Therefore, modelling index may vary between values such as 0 and 4. Vector j Ε must have a downward direction (preferibly between 45 and 75 to the vertical) in order to obtain a natural appearance of human features. Cylindrical / Horizontal An alternative concept to describe the modelling effect is the ratio between cylindrical illuminance and horizontal illuminance at a certain point. The average cylindrical illuminance Ε C at a point is average illuminance over a curved surface of a small cylinder located at the point (Fig. 7). Unless otherwise indicated, the cylinder axis must be vertical. EC Figure 7. Average cylindrical illuminance E C. Cylindrical illuminance at a point equals average vertical illuminance in all directions at such a point. A good modelling is achieved when the ratio is: 0.3 Ε C 3 Ε H Generally speaking, direction is automatically taken into account. Therefore, it is not necessary to specify it from an additional point of view, like in the case of vectorial / spherical ratio: when light comes directly from above, Ε C = 0 and Ε C / Ε H = 0; when light is horizontal, Ε H = 0 and Ε C / Ε H j q. Vertical / Semicylindrical Tests conducted in relation to lighting of pedestrian outodoor areas (low level lighting areas) have proved that the ratio between vertical illuminance and semicylindrical illuminance provides a useful measure of acceptance of human features modelling, for the mentioned application area. Semicylindrical illuminance Ε semicyl at a point in a given horizontal direction equals the average illuminance on a curved surface of a small vertical semicylinder located at such a point, with a curved surface focused towards the specified direction (Fig. 8). 64 LIGHTING ENGINEERING 2002

53 Chapter 6. FUNDAMENTAL PRINCIPLES Esem Figure 8. Semicylindrical illuminance. Well balanced lighting relief (neither very short nor very intense) is obtained at: 0.8 Ε V 1.3 Ε semicyl Extreme ratios are: Zero (π/2) = 1.57 very intense modelling. very short modelling Lambert s law There exist emitting or diffused surfaces that, when observing them from different angles, the same brightness feeling is obtained. These surfaces are called perfect emitters or diffusers. If L 0 is luminance according to the normal and L α is luminance according to the observation angle α, L α = L 0 is verified for any given angle α. Ι α Since L 0 = Ι 0 and L α =, the equation below is true: S S cos α Ι α = Ι 0 cosα This ratio is known as Lambert s Law and only perfect emitters or diffusers comply to it. N Lo Lα Io Iα α Surface Figure 9. Luminance invariability in relation to the incidence angle. LIGHTING ENGINEERING

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55 Chapter 7. LUMINAIRES 7.1. General remarks Luminaire classification according to the degree of protection from electric contacts Luminaire classification according to working conditions Luminaire classification according to mounting surface flammability Luminaire classification according to service conditions Photometric basic data Luminaire efficiency LIGHTING ENGINEERING

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57 Chapter 7. LUMINAIRES General remarks Due to the high luminance of lamps, it is necessary to increase the emission apparent surface in order to avoid visual problems (glare). Also, it is necessary to shield lamps to protect them from external agents and to direct their flux in the most convenient way for visual task. Thus, different studies and contemporary research place great emphasis on the combination formed by the source of light and the luminaire. According to the UNE-EN * Norm, a luminaire may be defined as a lighting apparatus which spreads, filters or transforms light emited by a lamp or lamps including all components necessary for supporting, fixing and protecting the lamps, (except for the lamps themselves). Should the need arise, also the auxiliary circuits combined with the media for the connection to the power supply. Main components Independently from other definitions which could be more or less descriptive, a luminaire may be defined as an object formed by a combination of elements designed to give an appropriate luminous radiation of an electric origin. Materialization of these elements is achieved by combining a good formal design and a reasonable economy of materials in each situation. Formal design solves luminous control depending on needs, which is the main aim: both a thermal control which makes its functioning stable and an electric control which offers adequate guarantees to the user. Economy of materials provides a solid and efficient product, an easily installed luminaire, and minimum maintenance while in use. Regarding the most fundamental characteristic components, body, control gear, reflector, diffuser, and filter among others, must be mentioned. All of them fall into other classifications shown below. 1. Body: This is the minimum physical element which supports and defines the volume of the luminaire and contains the key components. According to this criterion, several types may be defined: -For indoor or outdoor areas. - Surface or embedded mounted. - Suspended or rail mounted. -Wall, bracket or pole mounted. - Open or enclosed. -For normal or harsh environments (corrosion or explosion). 2. Control gear: Appropriate control gear would be selected to suit different sources of artificial light, according to the following classification: -Regular incandescent with no auxiliary elements. -High voltage halogene to regular voltage, or low voltage with converter or electronic source. -Fuorescent tubes. With reactances or ballasts, capacitors and starters, or electronic combinations of ignition and control. -Discharge. With reactances or ballasts, capacitors and starters, or electronic combinations of ignition and control. 3. Reflector: A specific surface inside the luminaire which models form and direction of the lamp flux. Depending on how luminous radiation is emitted, it may be: -Symmetric (with one or two axes) or asymmetric. -Narrow beam (lower than 20º) or wide beam (between 20 and 40º; greater than 40º). - Specular (with scarce luminous dispersion) or non specular (with flux dispersion). - Cold (with dicroic reflector) or normal. 4. Diffuser: This forms the cover of the luminaire in the direction of the luminous radiation. The most frequently found types are: - Opal (white) or prismatic (translucent). - Lamellae or reticular (with a direct influence on the shielding angle). - Specular or non specular (with similar characteristics to reflectors). 5. Filters: In possible combination with diffusers, they are used to protect or lessen certain characteristics of luminous radiation. *The UNE-EN Norm adopts the Internacional Norm CIE LIGHTING ENGINEERING

58 Chapter 7. LUMINAIRES 7.2. Luminaire classification according to the degree of protection from electric contacts Luminaires must secure protection of people from electric contacts. Depending on the degree of electric insulation, luminaires can be classified as: Class 0: Luminaire with basic insulation, lacking double insulation or overall reinforcement as well as an earth connection. Class I: Luminaire with functional basic insulation and an earth connection terminal or contact. Class II: Luminaire with double basic insulation and /or reinforced overall insulation lacking provision for earth discharge. Class III: Luminaire designed to be connected to extra-low voltage circuits, lacking internal or external circuits not working at an extra-low security voltage Luminaire classification according to working conditions The IP system (International Protection) established by the UNE-EN classifies luminaires according to their degree of protection from mechanical shock, dust and water. The term mechanical shock includes those elements like tools or fingers that are in contact with energy transmiting parts The designation to indicate degrees of protection consists in charateristic IP letters followed by two numbers (three in France) which indicate the compliance of conditions established in charts 1., 2. and 3. The first of these numbers is an indication of protection from dust, the second number indicates the degree of protection from water, whereas the third number, in the French system, indicates the degree of protection from mechanical shock. First characteristic numeral Brief description Symbol 0 Non-protected. No symbol 1 Protected against solid objects greater than 50 mm. No symbol 2 Protected against solid objects greater than 12.5 mm. No symbol 3 Protected against solid objects greater than 2.5 mm. No symbol 4 Protected against solid objects greater than 1 mm. No symbol 5 Dust- protected. 6 Dust tight. Chart 1. EN classification according to dust protection degree (1st numeral). Second characteristic numeral Brief description Symbol 0 Non- protected. No symbol 1 Protected against dripping water. 2 Protected against dripping water when tilted up to 15º. No symbol 3 Protected against dripping water when tilted up to 60º. 4 Protected against spraying water. 5 Protected against splashing water. 6 Protected against water jets. No symbol 7 Protected against the effects of immersion. 8 Protected against submersion. -m Chart 2. EN classification according to the degree of protection from water (2nd numeral). 70 LIGHTING ENGINEERING 2002

59 Chapter 7. LUMINAIRES Third numeral of the code This numeral refers to mechanical shock tests. The following chart shows characteristic numerals accompanied by a brief description. Third characteristic numeral Brief description Symbol 0 Non- protected No symbol 1 Protected against a J. mechanical shock No symbol 3 Protected against a 0.5 J. mechanical shock No symbol 5 Protected against a 2 J. mechanical shock No symbol 7 Protected against a 6 J. mechanical shock No symbol 9 Protected against a 20 J. mechanical shock No symbol Chart 3. EN classification depending on protection from mechanical shock. Instead of this third numeral, the EN Norm on Degrees of protection against external mechanical shock provided by electric material bulb (code IK) may also be applied. In the above mentioned Norm, the protection degree from mechanical shock provided by a bulb is indicated by the IK code in the way shown below: - Code letters (internacional mechanical shock protection): IK -Characteristic numerals: From 00 to 10 Each characteristic numeral represents a value for impact energy, whose correspondance is summarised in chart 4. IK Code IK00 Ik01 IK02 IK03 IK04 IK05 IK06 IK07 IK08 IK09 IK10 Mechanical shock in Joules. * Chart 4. Correspondence between the IK code and impact energy. Generally speaking, protection degree is applied to the bulb as a whole. If several parts of the bulb have different protection degrees, they must be indicated separately Luminaire classification according to the mounting surface flammability Luminaires cannot be mounted on any surface at hand. The surface flammability and the luminaire body temperature impose certain restrictions. Of course, if the surface is non-combustible, there is no problem. For classification purposes, the EN Norm defines flammable surfaces as usually flammable or easily flammable. The usual flammable classification refers to those materials whose ignition temperature is, at least, 200 ºC, degrees and do not weaken or deform at that temperature. The easily flammable classification refers to those materials which cannot be classified as usually flammable or non-combustible. Materials in this category may be used as mounting surface for luminaires. Suspended mounting is the only option for this type of material. In chart 5, mounting classification based on these requirements may be observed. Classification Luminaires suitable for direct mounting only on non- combustible surfaces. Luminaires suitable for direct mounting only on easily flammable surfaces. Symbol No symbol, but a warning notice is required. F On plaque. Chart 5. EN classification according to the mounting surface flammability. LIGHTING ENGINEERING

60 Chapter 7. LUMINAIRES 7.5. Luminaire classification according to service conditions Depending on their service conditions, luminaires fall into the following types: Indoor lighting luminaires Within this group, luminaires to illuminate premises and facilities in shopping areas, industries, offices, educational buildings, indoor sports facilities, etc. are found Therefore, this type of lighting tries to give the adecuate lighting for those working or teaching environments. Luminaires for general indoor lighting are classified by the C.I.E. according to the total percentage of luminous flux distributed above and below the horizontal plane. Luminaire type % Upward flux distribution % Downward flux distribution Direct Semi-direct Direct-indirect General diffuse Semi-indirect Indirect Chart 6. C.I.E. classification for indoor lighting luminaires. Direct Semi-direct General-diffuse 0~10% 10~40% 40~60% 90~100% 60~90% 40~60% Direct-indirect Semi-indirect Indirect 40~60% 60~90% 90~100% 40~60% 10~40% 0~10% Chart 1. Luminaire classification according to radiation of luminous flux. In turn, with regards to the symmetric flux emitted, a classification may be considered into two groups: 1) Symmetrical distribution luminaires: Those in which the luminous flux is spread symmetrically with respect to the symmetric axis and spatial distribution of luminous intensities. It may be represented as a single photometric curve. 2) Asymmetric distribution luminaires: Those in which the luminous flux is spread asymmetrically with respect to the symmetric axis and the spatial distribution of luminous intensities. It may expressed by a photometric solid, or, partially, by a flat curve of such a solid, depending on certain characteristic planes. Photometric information which accompanies indoor lighting luminaires Polar distribution curves These curves are generally represented in the coordinate system C-. Since there are infinite planes, in general, three C planes are represented, which are the following: 72 LIGHTING ENGINEERING 2002

61 Chapter 7. LUMINAIRES - Plane C = 0. - Plane C = Plane C = 90. Polar distribution curves are in the cd units per lumens of flux emited by the lamp. They are represented in cd/1 000 lm or cd/klm. (Fig. 2). C=90 C=45 C= Cd/Klm GM= Figure 2. Polar diagram in the C-γ system. Zone flux diagram These diagrams indicate the flux received by the surface to be illuminated directly from the luminaire, depending on angle γ. This diagram is obtained by creating cones whose axis coincide with the vertical axis of the luminaire. Generating angles with this axis are γ angles. The percentage of light collected by each of these cones is the image represented in the diagram (Fig. 3). 100% 80% 60% 40% 20% GM= Figure 3. Zone flux diagram. For narrow beam luminaires, a high flux percentage is obtained from small angles. This is the reason why the diagram will initially show a curve with a great slope for the first angles. From a certain angle onwards, it is virtually parallel to the abscissas axis. This is due to the fact that almost all flux is distributed in small angles, that is to say, it is concentrated in a small angle range. LIGHTING ENGINEERING

62 Chapter 7. LUMINAIRES For wide beam luminaires, the diagram will show a curve with a softer slope, since flux varies little by little, as the angle increases. Glare diagram These diagrams are based on the C.I.E. Glare Protection System. Curves representing these diagrams are of luminance limitation. Such curves cover a glare index scale (quality classes from A to E established by the C.I.E.) and different illuminance values in standard service. Two diagrams must be used depending on luminaire type and orientation according to vision. The required limitation of luminance depends on the luminaire type of orientation, shielding angle, acceptance degree or class quality, as well as on the value of the illuminance in service. In Figs. 4a and 4b, diagrams of luminance curves for the evaluation of direct glare are shown. Diagram 1 is for those directions of vision parallel to the longitudinal axis of any elongated luminaire and for luminaires which lack luminous lateral panels, observed from any direction. Diagram 2 is for those directions of vision in right angles to the longitudinal axis of any luminaire with luminous lateral panels. It is defined as: - Luminous laterals: A luminaire has luminous laterals is it possesses a luminous lateral panel with a height of more than 30 mm. - Elongated: A luminaire is elongated when the ratio between length and width of the luminous area is higher than 2:1. C=90 C=90 85 GM C=0 C=180 C=270 C=270 a b c d e f g h a/h Cd/m G Quality A B C D E Illuminance values in service E (lx) =< =< =< =< =<300 a b c d e f g h Figure 4a. Glare diagrams. 74 LIGHTING ENGINEERING 2002

63 Chapter 7. LUMINAIRES 85 GM G Quality A B C D E Illuminance values in service E (lx) =< =< =< =< =<300 a b c d e f g h ab c d e f g h a/h Cd/m C=0 C=180 Figure 4b. Glare diagrams. When using diagrams of Figs. 4a and 4b, luminance distribution of the luminaire in two vertical planes must be considered: the C 0 C 180 plane parallel to the inner axis. Luminance distribution of the luminaire in such a plane is used to control glare limitation in the longitudinal direction of the room. Distribution of the luminaire in the C 90 C 270 plane is used to verify glare limitation in the transverse direction to the place to be illuminated. When luminaires are mounted on the C 90 C 270 plane parallel to the longitudinal inner axis, such a plane must be used to verify glare limitation in the longitudinal direction of the place, and luminance distribution on the C 0 C 180 plane to avoid glare limitation in the transverse way of the place. For elongated luminaires, the C 90 C 270 plane is chosen to coincide with (or parallel to) the longitudinal axis of the lamp/s. When such a plane is parallel to the direction of the perceived vision, it is said to be longitudinal. However, when the C 90 C 270 plane is in right angles to the direction of vision, this vision is considered to be transverse. These diagrams are generally used for indoor lighting luminaires Road lighting luminaires Within this section, luminaires for parks and gardens as well as public road lighting are included. The first ones are frequently installed, as indicated by their name, in parks, gardens, residential areas, etc. The second ones are installed in urban roads, highways, tunnels, etc. The C.I.E. has introduced a new system for the classification of road lighting luminaires, thus, substituting the system introduced in 1965, where the classification was cut- off, semi cut- off and non cut- off. Nevertheless, the old system is still being used in certain national recommendations for road lighting. In chart 7, the old system is shown. Direction of Type of Allowed value for maximum intensity Allowed value for maximum intensity maximum intensity luminaire emitted at an elevation angle of 80 emitted at an elevation angle of 90 inferior to Cut off 30 cd / lm 10 cd / lm* 65 Semi cut off 100 cd / lm 50 cd / lm* 76 Non cut off Any - Chart 7. C.I.E. classification from LIGHTING ENGINEERING

64 Chapter 7. LUMINAIRES Cut- off Semi cut- off Non cut- off Figure 5. Examples of photometric curves accompanied by their classification. The new C.I.E. luminaire classification, which substitutes the previous one, is based on three basic properties of luminaires: 1. The extension to which the luminaire light is distributed along a path: the throw of the luminaire. 2. The amount of lateral dissemination of light, widthways of a path: the spread of the luminaire. 3. The reaching of the installation to control glare produced by the luminaire: the control of the luminaire. The reaching is defined by the angle γ max which forms the axis of the beam with the vertical plane going downwards. The axis of the beam is defined by the direction of the angle bisector formed by two directions of 90% Ι max in the vertical plane of maximum identity. 195 cd 130 cd 65 cd 65 cd 130 cd 195 cd 195 cd 130 cd 65 cd 65 cd 130 cd 195 cd 195 cd 130 cd 65 cd 65 cd 130 cd 195 cd 195 cd 130 cd 65 cd 65 cd 130 cd 195 cd Cut- off Axis of the beam γ max I max 90% Imax γ 0 Figure 6. Intensity polar curve in the plane which contains the maximum luminous intensity, indicated by the angle used to determine the throw. Three levels of throw are distinguished as follows: γ max < 60 : short throw. 70 γ max 60 : intermediate throw. γ max > 70 : long throw. * Up to a maximum absolute value of cd. 76 LIGHTING ENGINEERING 2002

65 Chapter 7. LUMINAIRES The spread is defined by the positioning of the line, running parallel to the axis of the path. Virtually, it does not touch the furthest side from the 90% I max on its path. The positioning of this line is defined by the γ 90 angle. The three levels of spread are defined in the following manner: γ 90 < 45 : narrow spread. 55 γ : average spread. γ 90 > 55 : broad spread. h γ 90 3h 2h 1h 90% Imax 4h Figure 7. Spread. Both the luminaire throw and spread may be more easily determined from an isocandela diagram in an azimuthal projection (Fig. 8). C 90% I max γ max γ γ 90 Figure 8. Isocandela diagram related to an azimuthal projection (sine wave) indicated by the γ max and γ 90 angles used to determine spread and throw. In Fig. 9 the covering given by the three levels of throw and spread of the luminaire mounting height (h) is indicated on a plane of the path. LIGHTING ENGINEERING

66 Chapter 7. LUMINAIRES Control is defined by the specific index, the luminaire SLI. This is part of the G formula of glare control, determined only by the features of the luminaire. ( I ) log ( I 80 ) SLI = log(i 80 ) log I 88 I log(f) + C where: I 80 = Luminous intensity at an elevation angle of 80, in a parallel plane to the axis of the roadway (cd). I 80 = Ratio between luminous intensities for 80 and 88. I 88 F = Light emission area for the luminaires (m 2 ) projected on the direction of the elevation at 76. C = Colour factor, variable according to lamp type (+0.4 for low pressure sodium and 0 for the others). h (90% Imax) 1.7h Short 2.7h 1h 1.4 h Intermediate Long Narrow Average Broad Spread γ max Figure 9. In this figure, the three degrees of throw and spread defined by the C.I.E. are shown, where h is the luminaire mounting height. Control is also classified into three levels, which are the following: SLI < 2 : limited control. 4 SLI 2 : moderate control. SLI > 4 : tight control. In the following chart, the C.I.E. previous definitions are summarised and shown. Throw Spread Control Short γ max < 60 Narrow γ 90 < 45 Limited SLI < 2 Intermediate 70 γ max 60 Average 55 γ Moderate 4 SLI 2 Long γ max > 70 Broad γ 90 > 55 Tight SLI > 4 Chart 8. The C.I.E. classification system depending on luminaire photometric properties. 78 LIGHTING ENGINEERING 2002

67 Chapter 7. LUMINAIRES Photometric information accompanying road lighting luminaires Diagrams of polar distribution curves These curves are generally represented for the coordinate system C-γ. Since there are infinite planes, usually there are three C planes represented, which are the following: - Transverse plane (C = 90 and 270 ). This plane would be perpendicular to the axis of the road for a road lighting luminaire. - Longitudinal plane (C = 0 and 180 ). This plane would be parallel to the axis of the road for a road lighting luminaire. - The plane in which maximum intensity is found. This plane is generally called main vertical plane. Polar distribution curves are defined in cd by lumens of flux emitted by each lamp and it is represented by cd/1 000 lm or cd/klm. TRANSVERSE PLANE (C=90-270) LONGITUDINAL PLANE (C=0-180) MAIN VERTICAL PLANE GM= GM= C=20.0 Figure 10. Polar diagram in the C- system. Isocandela diagrams It consists of imagining that the luminaire is in the center of a sphere; in its exterior surface equal intensity points are joined by a line. Equal surfaces in this diagram represent solid angles. Due to this reason, the diagram may be used to calculate luminous flux for a given area, multiplying the area by the luminous intensity (bearing in mind the scale in which the diagram is represented). If the luminaire is installed with a δ inclination angle, strokes must be turned around the center in an angle δ to deduce the new C-γ coordinates. Straight lines from the center represent parallel lines to the roadway axis C= GM= Imax=100% Figure 11. Isocandela diagram in azimuthal projection. LIGHTING ENGINEERING

68 Chapter 7. LUMINAIRES Diagram of isoluminance curves These diagrams are frequently used for public lighting. This is due to the fact that recommendations for public lighting are not exclusively limited to the average luminance required on the surface of the roadway, but also guidelines for their uniformity (ratio between L max and L min ) are provided. Such calculations are possible with the help of the isoluminance diagram (Fig 12). OBSERVERS: A, B AND C A B 6h 5h 4h h WALKWAY SIDE 0 3h 2h h 0 h 2h 3h C h 10 2h 3h ROADWAY SIDE Roadway R2 Qo = 0.07 Lmax=100% fl= Figure 12. Isoluminance diagram. In the diagram, letters A, B and C appear, indicating three positions for the observer which are used in luminance performance diagrams. Diagram of isolux or isoilluminance curves In practice, illuminances on the road surface and their total distribution are intended to be known in most lighting projects. In order to ease the determination of these data in an installation, photometric sheets provide us with the isolux relative curves for each luminaire on an illuminated plane. h WALKWAY SIDE h h ROADWAY SIDE 3h 6h 5h 4h Emax=100% fl= h 2h h 0 h 2h 3h Figure 13. Isolux diagram on the surface to be illuminated. Values for each isolux line are given in E max percentages, the highest being 100%. The lattice on which isolux lines are drawn is measured in terms of the luminaire mounting height h. 80 LIGHTING ENGINEERING 2002

69 Chapter 7. LUMINAIRES Under the diagram, a factor for the luminaire in use ( ) is indicated. Maximum illuminance is calculated by means of the following formula: where: ϕ = factor for the luminaire in use. Φ = lamp luminous flux. h = interdistance between luminaires. Ε max = ϕ. Φ h 2 Performance in luminances These diagrams are used to calculate average luminance on the surface of the roadway of a public lighting installation. If the pavement reflection class is known, the corresponding diagram will be used. Luminance performance diagrams are drawn in units of luminaire mounting height. Due to this reason, they are very useful for direct graphic uses C B A h 180 h 2h 3h 270 C=90 0 Figure 14. Performance in luminances with respect to three observers. Their reading is equal to that of utilization factor curves, except that the observer s position is important. Hence, curves are given for three observer s positions: A, B and C. - A: Observer located on a side of the sidewalk at a distance h of the row of luminaires. - B: Observer located in line with the row of luminaires. - C: Observer located on a side of the road at a distance h of the row of luminaires. LIGHTING ENGINEERING

70 Chapter 7. LUMINAIRES For other positions, it is necessary to interpolate. Average luminance is calculated with the following formula: L max = η L. Φ. Q o w. s where: η L = luminance performance factor. Φ = lamp luminous flux. Q O = average luminance coefficient. w = road width. s = interdistance between luminaires. Utilization factors In road lighting, utilization factor (h) is defined as the fraction of the luminous flux coming from a luminaire which, in fact, reaches the road. Utilization factor curves found on the photometric information sheets offer a simple method to calculate average illumination, which may be determined for a certain transverse section of the road. η = Φ used Φ lamp Utilization factor curves for a luminaire are understood as a function of transverse distances, measured in terms of h (mounting height) on the road surface, from the center of the luminaire up to each of the two curves (Fig. 15). 0.6 Walkway side Road way side η h C=90 h 2h 3h 0 Figure 15. Utilization factor as a function of h. The easiest and quickest way to calculate average illuminance of a straight road of infinite length is by using utilization factor curves: where: η = utilization factor. Φ = lamp luminous flux. n = number of lamps per luminaire. w = width of the road. s = interdistance between luminaires. Ε med = η. Φ. n w. s 82 LIGHTING ENGINEERING 2002

71 Chapter 7. LUMINAIRES Polar diagrams are frequently used for luminaires in: - Public lighting. - Lighting of parks and gardens Floodlight luminaires Within this section, those luminaires designed for installation in indoor and outdoor sports facilities, facades, working areas, invigilance areas, etc. A floodlight is a luminaire which concentrates the light in a solid angle determined by an optical system (mirrors or lenses), in order to achive a high luminous intensity. Lamps suitable for floodlights range from pressed glass lamps and halogen lamps and even high pressure mercury lamps, metal halide lamps and low pressure and high pressure sodium lamps. They all have different voltages and each provides a kind and special type of light, colour effects and efficiency. Mounting, relamping and cleaning must be done at a considerable height from the ground. Thus, an ergonomic design of the luminaire is required so that these tasks are easily taken care of. From the point of view of light distribution, floodlights are grouped in three basic types: symmetric, asymmetric and symmetric rotation. Floodlights are also classified according to the opening of the beam, as shown in chart 9. The opening of a floodlight beam (or beam angle) is defined as the angle, in a plane which contains the axis of the beam, on which luminous intensity decreases to reach a certain percentage (generally 50% or 10%) of its peak value (Fig. 16). Description Opening of the beam (at 50% Ι max ) Narrow beam < 20 Medium beam 20 to 40 Wide beam > 40 Chart 9. Classification of the beam opening. 50% I max β Imax Beam opening 50% I max Figure 16 For a floodlight with an intensity distribution of light in a symmetric rotational way (that is to say, distribution remains unchanged independently from the plane containing the axis of the beam under consideration), a figure for the opening of the beam may be established, for example 28 at both sides of the axis of the beam. For asymmetric distribution, as that given by rectangular fllodlights, two figures are given: for example 6 /24, since the beam is spread into two symmetric perpendicular planes (vertical and horizontal, respectively). Sometimes, distribution in the vertical plane of such floodlights is asymmetric in relation to the beam axis. In this kind of situation, two figures are given for the opening of the beam in this plane: for example, 5º - 8º/24º, that is to say, 5º above and 8º below the axis of the beam; and, in the LIGHTING ENGINEERING

72 Chapter 7. LUMINAIRES horizontal plane, 12º to the left and 12º to the right of the beam. Photometric information accompanying floodlights Cartesian diagram These diagrams are obtained in photometries performed on floodlights, since they provide us with information to be able to classify them according to beam opening They are generally represented under the coordinate system B-. Three lines representing the vertical plane, the horizontal plane and 50% of the maximum intensity (line parallel to the abscissas axis) are represented Horizontal plane Vertical plane Imax/ Figure 17. Cartesian diagram. Isocandela diagram In order to avoid coordinate curves, as it happens with solid angle systems, and ease the reading of coordinates, these are drawn in a rectangular system. The angles of C and B planes are on the horizontal axis, γ and β angles on the vertical one. The diagram may be compared with that of azimuthal projection, but, it must be taken into account that: - There is no linear ratio between rectangles in the diagram and solid angles. - The line γ = 0 or β = 0, in fact, represents a point. 84 LIGHTING ENGINEERING 2002

73 Chapter 7. LUMINAIRES Planes B AXIS X % of Imax Beta angles Figure 18. Isocandela diagram for the B- system Basic photometric data Luminaire information sheets show a series of diagrams which indicate their photometric peculiarities. In this section two terms associated to the obtention of such curves are going to be studied Photometric center Most calculations are done under the supposition that luminaires are specific sources of light. Thus, there is the need to search for a point in space limited by the luminaire which will place the specific equivalent and imaginary luminous source. For angles close to the nadir, there are virtually no differences between photometric data of the same luminaire given by different measurement laboratories. For big angles, there could be differences, for example 80º and 88º, if the photometric center of a luminaire is not clearly established. The photometric center is a point of a luminaire or a lamp from which the Law of the inverse square of the distance in the direction of maximum intensity is best complied. Or what is the same, it is the point where the imaginary and specific luminous source, with the same spatial distribution of luminous intensities of the luminaire is located. The only goal is to simplify photometric calculations. The C.I.E. has established in its publications the rules to locate such a photometric center for different types of luminaires Photometric coordinate systems Each and every one of the directions in the space through which luminous intensity is radiated is determined by two coordinates. On photometric information sheets for indoor luminaires, public lighting and floodlights, representations obtained by means of three coordinate systems, the most frequently used, are utilized. Such systems are A-α, B-β and C-γ. The C-γ coordinate system is defined in the C.I.E. publications. However, there is no international agreement on the definition LIGHTING ENGINEERING

74 Chapter 7. LUMINAIRES of the systems A-α and B-β. Tests for obtaining the last two differ depending on the country that conducts them. When applied to the photometry of these types of luminaires, the reference axis is always vertical and directed towards the lowest point (nadir). All systems have a beam of planes with an intersection axis, sometimes called rotation axis. In each case, a direction in space is characterized by an angle measured between two planes and an angle measured in one of the planes. Systems differ between themselves with regards to axis orientation of the intersection in space in relation to the luminaire axis. To test floodlights, systems adapted to the horizontal axis are used, but their name varies in different countries Luminaire efficiency Luminaire efficiency is expressed in terms of its Light Output Radio I.o.r.)*. This radio is defined as the portion of light output of the luminaire with regard to the sum of light individual exits of lamps when they are used outside the luminaire. The light output radio defined this way is the total I.o.r. of the luminaire, and is equal to the sum of the I.o.r. upwards and downwards. 86 LIGHTING ENGINEERING 2002

75 Capítulo 7. LUMINARIAS * The term used in the U.S.A. is luminaire efficiency. LUMINOTECNIA

76 Chapter 8. LAMPS 8.1. General remarks Thermal radiation Luminescence Conditions to be met by lamps Incandescent lamps High pressure mercury discharge lamps High pressure sodium discharge lamps Induction lamps Chart with characteristics LIGHTING ENGINEERING

77 88 LIGHTING ENGINEERING 2002

78 Chapter 8. LAMPS 8.1. General remarks In chapter 1, the dual nature of light was studied, and in chapter 2, the process of how visible radiations are manifested in light by means of vision was discussed. As it has already been mentioned, light is a form of energy represented by electromagnetic radiation, which may affect the human eye, and is produced in many ways, depending on the causes that provoke it. If it is due to the radiant body temperature, the phenomenon is called thermal radiation. All other examples are considered as luminiscence. Fig. 1 gives a general idea about the main physical agents which intervene in light production and their respective sources. LIGHT PRODUCTION Thermal radiation Incandescent combustion Gas discharge Luminiscence Solid body radiation Natural Sun Ray Glowworm Artificial Flame Gaslight Electric arc Incandescent lamp Metallic vapor lamp Noble gas lamp Negative glow lamp Xenon lamp Luminiscent substance Luminous plaque Solid body plaque Radioactive source of light Figure 1. Physical agents intervening in light production Thermal radiation It is the radiation (heat and light) emitted by a hot body. The energy of this radiation depends only on the calorific capacity of the radiant body. In general, the light obtained is always accompanied by a considerable thermal radiation that constitutes a source of energy loss when, in fact, light is trying to be produced. When heating a piece of coal, iron, gold, wolfram or any other material, a visible radiation is obtained. It may be seen in the incandescent colour acquired by the body and it will vary depending on temperature, as shown in Chart 1. Temperature C Incandescent colour red - incipient grey red - grey red - dark red - yellow red - light red - incipient white onwards red - white Chart 1. Incandescent colours at different temperatures. All the laws studied and formulated for the ideal radiator may be summarized in a single one: the percentage of visible radiation increases according to radiator temperature. As it may be seen in Fig. 2, at 6,500 K the maximum performance is obtained. It would be useless to increase temperature of the radiator with the intention of obtaining a performance greater than 40%. LIGHTING ENGINEERING

79 Chapter 8. LAMPS 50 % 40 Visible radiation percentage K Temperature Figure 2. Visible radiation depending on absolute temperature Natural thermal radiation In nature itself, an evident example of light production at a great scale may be found by the thermal radiation offered by the Sun or other stars similar to it. The Sun is an enormous ball of hydrogen in an incandescent state in which nuclear radiation is constantly transforming hydrogen (H 2 ) into Helium (He). In the process, enormous amounts of energy are expelled to the Universe. From the energy emitted by the Sun, almost 40% of the radiation is transformed into visible light, which corresponds to the maximum optical performance at 6,500 K Artificial thermal radiation Light by artificial thermal radiation is obtained by heating any solid matter or body at a high temperature, either through combustion or incandescence. Light of the lighting flame The oldest thermal radiator in history and also the most primitive one was the lighting flame produced by the combustion of a lit torch, followed by the oil lamp, the petroleum one and the wax candle, which were the most widely used lighting sources in the old times. At the beginning of the 19th century, the mineral coal gas (coal) was used to obtain a lighting flame, instead of the solid substances used until then (wax, grease) and liquid ones (oil, petroleum). At the beginning, light was obtained directly from the flame. Later on, through Auer's incandescent mantle. Electric arc light If two coal bars in contact, through which electric current is circulating, are quickly separated up to a certain distance, a permanent and powerful electric arc is produced between its pins. The electric arc itself only produces 5% of the emitted light. The rest corresponds to the incandescent craters formed in both coal bars. This kind of arc, whose current intensity is quite high, must not be confused with gas discharge arcs. Light of an incandescent body in the vacuum When an electric current circulates through an ohmic resistance, this is heated up and, if taking place in the vacuum, it turns incandescent. The colour acquired is red- white at temperatures ranging between 2,000 and 3,000 ºC, in which case it emits light and heat like a perfect thermal radiator. The first person who put this principle into practice was Henrich Goebel who made the first electric incandescent lamps in 1854, using empty perfume bottles in which he hermetically sealed a filament made with carbonized bamboo fibres. However, it was the American Thomas Alva Edison who discovered an incandescent lamp with 90 LIGHTING ENGINEERING 2002

80 Chapter 8. LAMPS a coal filament and gave it a practical utility as a series article in At the same time as Edison, the british Swan also achieved a usual incandescent lamp. The coal filament: Lamps used from 1880 to 1909, had a coal filament composed of coked bamboo or paper fibres. The point of fusion of this filament was approximately of 3,700 C, but due to its high vaporization index, lamps could also be made for a temperature in service of about 1,900 C. Thus, luminous performance was not more than 3 to 5 lm/w. The metal filament: At the beginning of the past century, a search begun in order to find metals that would be able to substitute the coal filament in a susccessful way. Among metals with a high degree of fusion were osmium, tantalium and wolfram mainly. Wolfram point of fusion is approximately 3,400 C, with an evaporation index slightly lower than that of coal. The lamp life is approximately 1,000 hours, the filament incandescence temperature reached 2,400 C and a luminous performance of 8 to 10 lm/w was obtained Luminescence Those luminous phenomena whose cause does not exclussively obey to temperature of the luminescent substance. Such phenomena are characterized because only some particles of the matter atoms, the electrons, are excited to produce electromagnetic radiations. In order to understand such a study, Börh s atomic model must be studied. Electrone energy ranges E e3 e2 e1 f A S f 1 f 2 W m E = Electron A= Absorption S= Emission = Energy emission 1 Weak excitation 3 Forced energetic excitation (laser) 6 Phosphorescence 2 Strong excitation 4 5 Stages emission, W heat give- away m = Acummulation level Figure 3. Böhr s atomic model. According to this model, each atom is formed by a positive atomic nucleus and by a cover of negative electrons. These are distributed in different layers that rotate around the nucleus following certain orbits. Usually there is an electric balance in the atom, that is to say, the number of positive charges is equal to the number of negative charges (electrons). This balance is known as fundamental state of the electron E, and for electrons in the most internal orbit, it is identical to the base line f (Fig. 3). If a certain amount of energy is administered to the electron from the outside, electron E is excited and moved from its regular orbit to the next one or to another more external one. Thus, the energy supplied is absorbed. The electron is located in a superior energy level (level lines e1, e2, e3, etc. of Fig. 3). After a short time in this level, the electron returns again to its regular initial position (line f of Fig. 3) and emits the amount of energy absorbed at the beginning, usually in the form of electromagnetic radiation. If the amount of energy is greater, electron E may instantaneously reach a more external orbit. As a consequence of the greater range of energy achieved, radiation emited when the electron returns to base f will be richer in energy. Therefore, the different layers of energy correspond to a perfectly determined level of energy, and, thus, there are not intermediate levels. Thus, it is deduced that in order to excite an atom, an exactly determined amount of energy is necessary. This is emitted in the form of radiation and/ or heat loss when the atom recovers its fundamental shape. LIGHTING ENGINEERING

81 Chapter 8. LAMPS The emission of energy transformed in this process from an atomic point of view takes place in portions or discontinuous parts known as energy quants (Böhr postulated that the atom may not rotate at any distance from the nucleus, but in certain orbits only). However, in the field of practical lighting engineering, light emitted in this tranformation is considered to be emitted in a continuous way, in the form of electromagnetic waves, which is acceptable for normal cases of its application. By means of the theory of energy quants formulated by Max Plank, it is proved that different chemical elements, when excited, do not emit a continuous spectrum due to the different structure of their electronic layers, but only very particular wavelengths (lines) within all the electromagnetic spectrum. These spectra are known as linear spectra. Each substance has a characteristic linear spectrum and also luminescent gases like, sodium vapor, whose spectrum is composed by a double yellow line whose wavelengths correspond to 589 and nm, respectively. According to the physical technique used to excite atoms, the type of radiation and the form in which it is emitted, several types of luminiscence may be distinguished. Electric discharge light within a gas In all gases, especially in those contained in discharge lamps, besides neutral gas atoms, some free electric charges are found (electrons). E A Figure 4. Gas discharge tube. E C If a continuous current is applied to the anode A (+) and to the cathode C (-) of the discharge tube (Fig. 4), an electric field is created between A and C which accelerates negative charges (electrons) and hurries them towards the anode. When an electron reaches a certain speed, it has enough kinetic energy to excite a gas atom. If the speed of the electron when crashing against the atom gas is even greater, the impact may even cause the separation of an electron from the atomic cortex, so the atom lacks an electron in its configuration. That is to say, a positive ion is obtained. This phenomenon is known as impact ionization. This way, the number of free electrons is even higher. It is even possible that they will increase enormously if the electric current produced by them is not limited by means of an appropriate resistance (stabilizer). Together with the free or separated electrons, positive ions may be also found moving in the opposite way of electrons. That is to say, towards the cathode. Due to their small speed, they may not produce any excitation of other gaseous particles. On the contrary, after a short period of time, they take an electron again in exchange for an energy emission. Depending on the noble gas or metal gas with which the discharge container is filled, by means of the previously mentioned atomic excitation, linear spectra or light colours characteristic of the chosen chemical element will be formed. For example, if the gas is neon, the light colour is red- orangish, and if it is mercury vapor, it will be white- bluish. All these phenomena take place within a volume ranging between two electrodes, and it is limited by the discharge container wall. This volume forms a discharge gaseous column. If the discharge tube receives an alternating power supply, instead of a continuous one, electrodes change their function periodically, sometimes behaving as a cathode and some other times as an anode. Otherwise, the luminous production phenomenon is exactly the same. Electric discharge conditions for light production in a gas essentially depend on the gas or vapor pressure inside the discharge tube. So, there are three kinds of discharge, namely: -Low pressure discharge. -High pressure discharge. 92 LIGHTING ENGINEERING 2002

82 Chapter 8. LAMPS -Very high pressure discharge. The higher pressure is, the wider spectral lines, forming even greater bands, so that the chromatic spectrum improves. Metal vapor lamps need the metal to be vaporized first since it is in a solid or liquid state when cold. This is the reason why these lamps are filled with a noble gas which is the first one to inflame, supplying the heat necessary for metal vaporization. High voltage electric discharge between cold electrodes (noble gas tubes) In order to administer enough free electrons in this type of discharge, cold electrodes are used mostly built with a chromiumnickel metal. The filling of the discharge tube is with noble gases like neon which emits an intense red- orangish light, or helium which emits a light pink coloured light and also with metal vapors, especially mercury vapor which emits a white- bluish light, and when mixed with the neon gas an intense blue light. Starting and working voltages are high, 600 to 1,000 volts being necessary for half a metre in length. The average voltage consumption also for half a metre in length is of about 33 W, with a luminous performance of 2.5 to 5 lm/w. Due to this low luminous performance, noble gas tubes have been barely used for indoor lighting, but they really have played an important role in luminous advertisement due to their particular easiness to be modelled in the shape of letters. Low voltage electric discharge between hot electrodes (metal vapor lamps) If a certain amount of solid sodium or liquid mercury is introduced inside a glass tube previously evacuated in order to transform metal into vapor through the electric discharge, a metal vapor discharge in gas is obtained. This may be even produced at a regular low voltage (220 V), with prehated or heated electrodes (hot cathodes). Sodium and mercury vapor lamps work according to this principle. From everything that has been exposed until now, it is deduced that light emitted by metal vapor lamps especially depends on the linear spectrum of the metal vapor chosen. Thus, sodium vapor lamps produce a monochromatic light of a yellow- orangish light and mercury vapor lamps one of a green- bluish characteristic. Discontinuous spectra of these lamps are improved through different ways: Mercury lamps: -Through combination with an incandescent lamp (blended light lamps). -Through combination with a fluorescent layer (mercury vapor lamps, corrected colour). -Through addition of metal halides (metal halide vapor lamps). Sodium lamps: -Through combination with mercury light in a metal transparent recipient, at high pressure filling (high pressure sodium lamps). Photoluminescence (low pressure fluorescent lamps) Photoluminescence is fundamentally understood as the excitation of certain substances to luminescence by means of radiation, usually produced by short wave ultraviolet radiation. The luminescent substances used only emit light while they are being excited by short wave ultraviolet radiation which is transformed into a longer wave radiation (visible spectrum light). Luminescent substances used are, among others, calcium wolfram, magnesium wolframite, zinc silicate, cadmium silicate, cadmium borate, halophosphates, etc. Each of these luminescent substances emits a certain light colour. By mixing these substances in an appropriate way, any desired composed light colour may be obtained. If the emission light of each of these chromatic components is achieved to be superimposed, a continuous spectrum is obtained which may also vary from daylight white to warm white. Fluorescence are all those luminescent phenomena in which luminous radiation remains during the excitation. The opposite situation is known as phosphorescence. LIGHTING ENGINEERING

83 Chapter 8. LAMPS Phosphorescence Phosphorescence takes place when luminous radiation persists in certain luminescent substances even after excitation is over. This phenomenon corresponds to the fact that under certain energy levels (belonging to certain electronic layers) of some chemical components, like sulphures, seleniures or oxides of alkali earth metals, apart from this, there is an acummulation level that prevents electrons from quickly returning to their initial position. Electrons, that because of their excitation reach this acummulation level, can only in a slow fashion recover their fundamental state. It is then when the substance continues emitting light. This phenomenon may last fractions of seconds or months (depending on material type and temperature). Electroluminance In order to produce this phenomenon, instead of an exciting radiation, also an electric field may be directly used to rise electrons at a higher level of energy. This is achieved by inserting a luminescent substance between two conducting layers and applying alternating current to the group, as for plaque condensers. This way to obtain light (manifested by a sparkle of a moderate splendor) has been performed in the so- called luminous plaques to be applied in hospital rooms, building numbering, stair lighting, etc. Injected luminescence To a certain extent, it is the opposite case to that of the photoelectric principle, in which photometres to measure light are based. Whereas there is a luminous energy transformation in the photometre into electric energy (in the form of a minicurrent), on applying injected luminescence to the so- called solid body lamp of an electric energy, a luminous energy is reciprocally produced (chromatic radiation). This kind of radiation has a very good application for simple procedures of unimportant marking. A solid body lamp is obtained by inlay in the net of a semiconductor certain strange atoms, in such a way, that it will remain divided into two parts, one with an excess of electrons and the other with a defect. Radioluminescence (light produced by radioactive substances) In this case, the luminous emission is based on radiation from a luminescent substance with rays which result from the natural desintegration of radioactive matter, like for example, uranium and its isotopes. This light production principle, the so- called isotope lamp, is applied which does not need power supply at all to work. Bioluminescence Bioluminescence is a luminous phenomenon which is weakly manifested in Nature. It consists of a sparkle emitted by light worms, some classes of fishes, marine algae, rotten wood and similar. This phenomenon is due to the oxidation process of some special chemical or organic substances, like the ones glow worms and photogene bacteriae have when in contact with the air or water oxygen. So far, it has not been possible to reproduce this phenomenon of Nature artificially Conditions to be met by lamps Total radiation spectral distribution For lamps as energy transformers to work with a high performance, almost all the energy absorbed should be transformed into visible radiation. Besides, their light should be white like daylight and with a good chromatic reproduction which requires a continuous spectrum containing all main colours from purple to red. But, since eye sensitivity is maximum for yellow- greenish radiation, the best thing to do, as far as luminous performance is concerned, is to obtain the highest percentage possible of radiation in the 555 nm zone. 94 LIGHTING ENGINEERING 2002

84 Chapter 8. LAMPS Luminance Light lamps preferably used outside must not have a high luminance so that their glare effect is kept within bearable limits. The admissible luminance value depends on the type of application. On the contrary, lamps used in luminaires may have great luminances, since they trimmer the glare effect. In general, luminance to be obtained from a lamp depends on the system adopted for light production, that is to say, on the physical nature of the source of light and on the fact that it may be pointed, linear or plane. Lamps luminance may never be increased by means of any optical system but it may be weakened, for example by diffusing layers Luminous intensity distribution Lamp radiation is not equal in all directions in the space. It is affected by the position of the base, the supports of the luminous body, etc. All this determines that each type of lamp possesses a distribution typical of its luminous intensity. Luminous distribution curves are essential to project lighting installations, as well as for luminaire design, because their optical system must be adjusted in such a way to the lamp luminous distribution curve and light is directed to the place or point where it is needed the most Emitted radiation biological effect Lamps must not emit any unnecessary or harmful radiation for human beings, either immediately or in the long run. With thermal radiators like incandescent lamps, this condition is observed from the beginning (most of the radiation produced is infrared). Some gas discharges, mainly mercury vapor, naturally contain a percentage of ultraviolet radiation that may be classified into: - UV-A: Sun tanned or long wave (between 315 and 380 nm.). - UV-B: Anti- rachitic or medium wave (between 280 and 315 nm.). It favours the production of vitamin D in the body. - UV-C: Bactericide or short wave (between 200 and 280 nm.). It kills germs and organic matter. These effects may increase due to weakening of the atmospheric ozone layer. - UV-C: Ozonosphere or short wave (between 100 and 200 nm.). This type of radiation is able to create ozone with the same characteristics as that of the atmosphere. The permanent effect of UV-B or UV-C radiations produces burns on the skin and conjunctivitis in the eyes which are not protected. In general lighting lamps, this may be avoided with the use of appropriate glass classes that absorb critical radiation Appropriate colour for each application The light colour of a lamp is determined by the spectral composition of its radiation. In Chart 2, light groups are established for lamps used in general lighting: Light colour Incandescent-fluorescent Warm white White or neutral white Cold white Daylight white Color temperature K K K K K Chart 2 Whereas incandescent lamps, due to their high content in the power supply (with the exception of coloured lamps), may only radiate a warm white colour, light colours of discharge lamps are determined by gases or vapors chosen for them. For example, LIGHTING ENGINEERING

85 Chapter 8. LAMPS yellow for sodium vapor discharge, or pale blue for mercury vapor. Other chromatic variants may be used, combining different metallic vapors or modifying vapor pressure. With fluorescent lamps the possibility of achieving any shade that may be desired is offered by means of the selection or mixture of a great amount of well- known luminescent substances, in order to adapt them to each type of application Chromatic reproduction quality Chromatic reproduction refers to the aspect of the colour illuminated surfaces have. Their reproductive quality not only depends on the incident light colour tone, but also on their spectral composition. Therefore, colour temperature technically refers to the colour of light, but not to its spectral composition. Thus, two sources of light may have a very similar colour and have, at the same time, some very different chromatic reproduction properties. Most of the times what is required from a lamp is a good chromatic reproduction, which means a spectral distribution different from the necessary one to obtain a high luminous performance Luminous flux constants In practice, it is not possible to maintain the luminous flux value at a 100% during all the life of the source of light, since physical and technological reasons are against it. Luminous flux indicated in catalogues refer, as far as incandescent lamps are concerned, to lamps which have not been working yet, and as far as discharge lamps are concerned, to lamps with 100 hours of working, to which this has been stabilized Luminous performance As seen in chapter 5, the maximum luminous performance to be achieved in the most favourable situation is 683 lm/w. Although this value may not be reached, nowadays, lamps with a quite high performance have been achieved that allow the obtaining of high lighting in a relatively economic way. Nevertheless, in many cases it must be decided which property of the lamp is the most priceless: whether a high luminous performance or an extraordinarily good chromatic reproduction Average rated life and service life Average rated life is an statistical concept which represents the arithmetic means of the duration in hours of each of the lamps of a group representative enough of the same model and type. Service life is a measurement referred to practice, also given in hours, after which the luminous flux of a certain lighting installation has decreased to such a value that the lamp is not profitable although the lamp may go on working Repercussions in power supply Any modern lamp requires its working not to have an important repercussion in the power supply. With incandescent lamps, this repercussion is limited to an upsurge in the connection moment, due to its small resistance with the cold lamp. Electric discharge lamps generally work in connection with an inductance, representing an apparent resistance for the circuit. This gives rise to obtaining a low power factor (cos ), which means an additional charge for the power supply and it must be then compensated Stabilization of lamps with negative resistance characteristics Negative resistance is the property some electric resistances have, for example, a discharge arc one, to decrease its value as the intensity of the current circulating through it increases. This obliges to stabilize current in discharge lamps so that it will not acquire excessive values that may destroy it. This is easily done by locating inductive, capacitive and ohmic resistances in the lamp circuit. 96 LIGHTING ENGINEERING 2002

86 Chapter 8. LAMPS Variations in power supply Variations in power supply influence the lighting engineering data of any lamp. In incandescent lamps, they affect duration and colour temperature very much, and in discharge ones, relations of arc pressure and also discharge conditions Time needed until the luminous flux acquires the normal regime Incandescent lamps ignite immediataly emiting their total flux. Fluorescent lamps may also do it if quick ignition starters are used. If not, ignition will be done later on, after one or several attempts. The other discharge lamps require some minutes as ignition time, until metal vapor acquires the necessary pressure and the luminous flux reaches it maximum value Possibility of immediate reignition It is the possibility that a lamp, after having been turned off, will be immediately reignited while still hot with full emission of the luminous flux. This condition is only met by incandescent lamps, metal vapor ones present certain differences regarding their immediate reignition possibility, as indicated below: - High pressure mercury lamps: They need some time (minutes) for cooling down before reignition while still hot, and some more time to reach the total luminous flux. - Metal halide lamps: They behave exactly like mercury ones. There are some types which may reignite while still hot by means of special devices. - High pressure sodium lamps: Those types which have a separated ignition device reignite while still hot within a minute and reach their total flux virtually with no delay. Other types without a separate ignition device behave in a similar fashion as mercury lamps. - Low pressure sodium lamps: They behave like mercury lamps Stroboscopic effect In all artificial sources of light which work with alternating current their emission stops every time current goes through the zero point. This takes place twice per period, so for a 50 Hz. frequency (periods per second) corresponds 100 instants of darkness per second. The filament of incandescent lamps has a lot of thermal inertia. Thus, a slight descend of luminous emission takes place due to such a reason. This is not perceived by the eye except when low power lamps work with a 25 Hz voltage. For discharge lamps working with 50 Hz. voltages, the eye is not able to appreciate such quick light variations which are produced. It may be the case, too, that lamps illuminate zones in which rapid movements are made, these being observed as if they were made intermittently or even as if they were stationary. This phenomenon is known as the stroboscopic effect and it may be reduced to make it unobservable by means of a lamp special power supply mounting, or wherever a three- phased line is available, distributing its connection between the three phases Working position An electric lamp is generally made for a certain working position in which it has optimal working properties. Outside this position, properties worsen, either by an excess of heating of the spiral, the base or the glass outer bulb, by deviation of the discharge lamp arc or by variations of the surrounding heat. This is the reason why tolerances given in the corresponding lamp catalogues must be accepted in order to avoid their premature depletion because of an inadequate working position. Abbreviations used indicate the main working positions and the admissible tilt angle in degrees. Main working positions: S (s) = Vertical (standing, base downwards). H (h) = Vertical (hanging, base upwards). P (p) = Horizontal (base sideways). LIGHTING ENGINEERING

87 Chapter 8. LAMPS HS (hs) = Vertical (base upwards or sideways). Universal = Allows any position. Admissible tilt angles: After the main working position, there is a figure that indicates the admissible tilt in degrees in relation to it p 20 p 45 p 60 h h 110 h 150 hs 30 hs 45 NON admissible position Admissible position Figure 5. Working position sketch. 98 LIGHTING ENGINEERING 2002

88 Chapter 8. LAMPS 8.5. Incandescent lamps As it has been said before, the incandescent lamp is the oldest source of electric light and, nowadays, the most commonly used one. It is also the one that possesses the widest variety of alternatives and it may be found in almost all installations, specially when a low luminous flux is required. A relatively recent discovery is the halogene incandescent wolfram lamp, which has quickly dominated many lighting application areas Conventional incandescent lamps Incandescent lamps produce light through the electric heating of a wire (the filament) at a high temperature, emitting radiation within the visible field of the spectrum. Base Filament Filling gas Figure 6. Conventional incandescent lamp. The main parts of an incandescent lamp are the filament, the filament supports, the glass bulb, the filling gas and the base. Filament: The one used in modern lamps is made out of wolfram (high fusion point and low evaporation degree). A higher luminous efficiency would be achieved by twisting the filament as an spiral. Glass bulb: It is a cover of sealed glass which encloses the filament and avoids contact with the air outside (so that it does not burn). Filling gas: Filament evaporation is reduced filling the glass bulb with an inert gas. The most commonly used gases are argon and nitrogen. In these lamps, luminous energy obtained is very little compared to the heat energy irradiated, that is to say, a great amount of the transformed electric energy is lost as heat and its luminous efficacy is small (it is a waste- energy lamp). The advantage of these lamps is that they are directly connected to the electric current without the need of an auxiliary equipment for their working Wolfram halogen lamps The high temperature of the filament for a normal incandescent lamp makes wolfram particles to evaporate and condense on the wall of the glass bulb, darkening this, as a result. Halogen lamps have a halogen component (iodine, chlorine, bromine), added to the filling gas and work with the halogen regenerative cycle to prevent darkening. The evaporated wolfram is combined with the halogene to form a halogene wolfram compose. As opposed to wolfram vapor, it is maintained in the form of gas, the glass bulb temperature being high enough as to prevent condensation. When such a gas approaches the incandescent filament, it is decomposed due to the high temperature in wolfram that is again deposited in the filament, and in halogene, which continues with its task within the regenerative cycle (Fig. 7). LIGHTING ENGINEERING

89 Chapter 8. LAMPS Temperature lower than 1 400º C Temperature higher than 1 400º C Tungsten filament Tungsten halide Halogenes Tungstene particles Glass bulb Figure 7. Halogene cycle. The main difference between an incandescent lamp, apart from the halogene additive mentioned before, is in the glass bulb. Due to the fact that temperature of the glass bulb must be high, halogene lamps are of a smaller size than regular incandescent lamps. Their tubular- shaped glass bulb is made out of a special quartz glass (which must not be touched with the fingers). Since their introduction, wolfram halogene lamps have entered almost all applications where incandescent lamps were used. The advantages of wolfram halogene lamps with regard to regular incandescent lamps are the following: longer duration, greater luminous efficiency, smaller size, greater colour temperature and little or no luminous depreciation in time High pressure mercury discharge lamps In this section, discharge lamps in whose discharge tube mercury is introduced, are going to be studied. Fluorescent lamps, compact fluorescent lamps, high pressure mercury lamps, blended light lamps and metal halogene lamps are included Fluorescent tubes Fluorescent tubes are a low pressure mercury discharge lamp in which light is produced predominantly through fluorescent powder activated by the discharge ultraviolet energy. The lamp, generally with a long tubular- shaped glass bulb and a sealed electrode for each terminal, contains low pressure mercury and a small amount of inter gas for ignition and arc regulation. The glass bulb inner surface is covered by a luminiscent substance (fluorescent powder or phosphorous) whose composition determines the amount of emitted light and the lamp colour temperature). Lamp holder Fluorescent coat (luminophorous). Visible light Wolfram electrodes with electron emitting matter Free electron Ultraviolet radiations Mercury atom Argon and mercury atmosphere Transparent glass tube Length Figure 8. Fluorescent lamp. 100 LIGHTING ENGINEERING 2002

90 Chapter 8. LAMPS The main parts of the fluorescent lamp are the glass tube, the fluorescent layer, the electrodes, the filling gas and the base. Glass tube: The glass tube of a regular fluorescent lamp is made out of sodium- calcium glass softened with iron oxide to control short wave ultraviolet transmission. Fluorescent covering: The most important factor to determine the characteristics of the light of a fluorescent lamp is the type and composition of the fluorescent powder (or phosphorous) used. This establishes colour temperature (and, as a consequence, colour appearance), colour reproduction index (R) and, lamp luminous efficiency, to a great extent. Three groups of phosphorous are used to produce different series of lamps with different colour qualities (standard phosphorous, tri- phosphorous and multi- phosphorous). Electrodes: Electrodes of a lamp which possesses an adequate layer of material emitter serve to drive electric energy to the lamp and provide the necessary electrons to maintain discharge. The majority of fluorescent tubes have electrodes that are preheated by means of an electrical current just before ignition (they are given the name of preheating electrode lamps; this preheating is begun by an independent starter). Filling gas: Filling gas of a fluorescent lamp consists in a mixture of saturated mercury and an inert gas trimmer (argon and krypton). Under normal working conditions, mercury is found in the discharge tube both as a liquid and as vapor. The best performance is achieved with a mercury pressure of about 0.8 Pa., combined with a pressure of the trimmer of about Pa. (0.025 atmospheres). Under these conditions, about 90% of the radiated energy is emitted in the ultraviolet wave of nm. In fluorescent lamps, colour temperature ranges between K and K., with a discontinuous spectral distribution curve reproducing colours depending on the composition of the fluorescent substance that covers the inner wall of the tube. Each resulting total luminous radiation is the sum of the radiation of discontinuous spectrum plus that of a continuous spectral distribution, more efficient each time, with the use of special phosphorous. Thus, fluorescent tubes with several light tones and chromatic reproduction indexes are manufactured. According to the C.I.E. norms, these are divided into three main groups: - Daytime white light: T C > K. -Neutral white: K T C K. -Warm white: T C < K. There are several tones for each group, with a wide range of colour temperatures and chromatic reproduction indexes, depending on each manufacturer. These cover the needs for a wide range of applications. These lamps require an auxiliary equipment formed by a ballast and an igniter (starter), besides a compensation condenser to improve the power factor. Working nominal values are reached after five minutes. When the lamp is turned off, due to a great pressure in the burner, it is necessary to cool down between four and fifteen minutes before it is turned back on High pressure mercury lamps Since their introduction, high pressure mercury lamps have been developed to a point that lighting technology cannot be thought of without it. In these lamps, discharge takes place in a quartz discharge tube containing a small amount of mercury and an inert gas filling, usually argon, to help ignition. One part of the discharge radiation occurs in the visible region of the spectrum as light, but some part is also emitted in the ultraviolet one. Covering the inner surface of the blister, in which the discharge tube is located, with a fluorescent powder which will transform this ultraviolet radiation into visible radiation. The lamp will offer higher lighting than a similar version without such a layer. Working principles When the working of the high pressure mercury lamp is examined, three well differentiated phases must be distinguished: ignition, turn-on and stabilization. LIGHTING ENGINEERING

91 Chapter 8. LAMPS Ignition Ignition is achieved by means of an auxiliary electrode, placed very close to the main electrode and connected to the other through a high value resistance (25 kω). When the lamp is turned on, a high voltage gradient takes place between the main and the ignition electrodes, which ionizes the filling gas in this area as a luminescent discharge, the current being limited by a resistance. Luminescent discharge is then expanded through the discharge tube under the influence of the electric field between the two main electrodes. When luminescent discharge reaches the most distant electrode, current increases in a considerable way. As a result, the main electrodes are heated until the emission increases enough to allow the luminescent discharge to change completely to an arch discharge. The auxiliary electrode lacks another function in the process as a consequence of the high resistance connected serially to it. During this stage, the lamp works as a low pressure discharge (similar to that of a fluorescent lamp). The discharge fills the tube and gives it a bluish appearance. la corriente limitada por una resistencia. La descarga luminiscente luego se expande por todo el tubo de descarga bajo la influencia del campo eléctrico entre los dos electrodos principales. Turn- on The inert gas having been ionized, yet, the lamp does not burn in the desired way and does not offer its maximum production of light, until mercury present in the discharge tube is completely vaporized. This does not happen until a certain amount of time has elapsed, called turn-on time. As a result of the arch discharge in the inert gas a heating is generated providing a quick increase of temperature inside the discharge tube. This causes mercury gradual vaporization, increasing vapor pressure and concentrating discharge towards a narrow band along the axis of the tube. With an increase in pressure, radiated energy progressively concentrates along the spectral lines of greater wavelengths and a small portion of continuous radiation is introduced. This way, light turns whiter. With time, the arc achieves a stabilization point and it is said that the lamp reaches the total thermodynamic balance point. All mercury is then evaporated, and discharge occurs in non- saturated mercury vapor. The turn- on time, defined as the necessary time for the lamp since the ignition moment to reach an 80% of its maximum production of light, is approximately four minutes. Stabilization The high pressure mercury lamp, like most discharge lamps, has a negative resistance and, thus, it cannot work on its own in a circuit without an adequate ballast to stabilize the flux of the current through it. Main parts In Fig. 9 the main parts of a high pressure mercury lamp may be observed. Base Wire beam lead Hard glass ovaloidal glass bulb Fluorescent substance Ohmic resistance for each auxiliary electrode in series Low pressure inert gas filling Auxiliary electrodes Discharge tube Principal electrodes Support Wire beam lead Figure 9. High pressure mercury lamp. 102 LIGHTING ENGINEERING 2002

92 Chapter 8. LAMPS Discharge and support tube: The discharge tube is made out of quartz. It has a low absorption of ultraviolet and visible radiation. Also, it stands high temperatures of the work involved. Electrodes: Each main electrode is composed of a wolfram bar, whose extreme is covered by wolfram serpentine impregnated with a material that favors the emission of electrons. The auxiliary electrode is simply a piece of wire of molybdenum or wolfram located near one of the main electrodes and connected to another one by means of a resistance of 25 kω. Blister: For lamps up to 125 W of potency, the blister may be of glass sodium- calcium. However, lamps with higher potencies are manufactured, generally, with hard glass of borosilicate, since higher working temperatures and thermal shock are tolerated. The blister, which normally contains an inert gas (argon or a mixture of argon and nitrogen), protects the discharge tube from changes in the room temperature and protects lamp components from corrosion. Glass covering: In most high pressure mercury lamps, the inner surface of the blister is covered by white phosphorous to improve lamp colour reproduction and to increase its luminous flux. Phosphorous transforms a great amount of ultraviolet energy radiated by the discharge into visible radiation, predominantly in the red extreme of the spectrum. Gas filling: The discharge tube is filled with an inert gas (argon) and a precise dosis of distilled mercury. The first is necessary to help originate the discharge and to secure a reasonable life for the covered emission electrodes. The blister is filled with argon or with a mixture of argon and nitrogen at atmospheric pressure. The addition of nitrogen serves to avoid an electronic arc between the wire supports of the glass. These lamps require an auxiliary equipment which is normally a ballast with an inductive resistance or transformer of the dispersion field, besides a compensation condenser. When the lamp is turned off, it will not start again until it has cooled off enough to lower vapor pressure to the point where the arc will be turned on again. This period lasts about minutes Blended light lamps Blended light lamps are a combination of the high pressure mercury lamp and an incandescent lamp. They are a result of one of the tries to correct bluish light of mercury lamps, which is achieved by inclusion within the glass itself, of a mercury discharge tube and a wolfram incandescent filament. Mercury discharge light and that of the fired filament are combined, or mixed, to achieve a lamp with totally different operative characteristics compared to those which have both pure mercury lamp and an incandescent lamp. Main parts With the exception of the filament and the gas used in the blister, parts of a blended light lamp are the same as those described for high pressure mercury lamps (Fig. 10). Base Wire beam lead Hard glass ovoid glass bulb Fluorescent substance Low pressure inert gas filling Tractional resistence Discharge tube Incandescent filament Principal electrodes Figure 10. Blended light lamp. LIGHTING ENGINEERING

93 Chapter 8. LAMPS Filament: The filament, which also acts as a resistance ballast for the discharge tube, is a coiled wolfram wire the same as that of the incandescent lamp. It is connected with the discharge tube in series and located next or around it, to obtain a good blended light and to favour a quick ignition of the tube. Filling gas blister: As for incandescent lamps, the filling gas in blended light lamps is made out of argon but adding a percentage of nitrogen to avoid an arc in the filament. Compared with the standard high pressure mercury lamp, a greater filling pressure to keep evaporation of wolfram to the minimum is used. Blended light lamps have the advantage of being connected directly to the power supply system (ballast and starter for is not required their working). Ignition takes about two minutes and re- ignition is not possible before cooling- down Metal halide lamps High pressure mercury lamps also contain rare earths like Dysprosium (Dy), Holmium (Ho) and Thulium (Tm). These halides are partly vaporized when the lamp reaches its normal working temperature. Halide vapor is later on dissociated, within the hot central zone of the arc, into halogene and metal, achieving a considerable increase of luminous efficacy and approaching colour to that of daylight. Different halide combinations (sodium, iodine, ozone) are used to which scandium, thallium, indium, lithium, etc. is added. Main parts Base Base Clear tubular glass bulb Electrodes Quartz discharge tube Ellipsoidal diffuser glass bulb Figure 11. Metal halide lamps. Discharge tube: It is made out of pure quartz. Sometimes, a white layer of zirconium oxide is applied to the outer part of the electrode cavities, to increase wall temperature at that point. Electrodes: They are similar to those of the high pressure mercury lamp. Blister: The blister of metal halide lamps is made out of hard or quartz glass. Some do not even have an blister. The inner surface of blisters with an ovoid shape has a phosphorous layer to transform discharge ultraviolet radiation into visible radiation. However, halides used for the metal halide lamp produce only a small amount of ultraviolet, and mainly, it is radiated in the ultraviolet spectrum wavelength zone, where conversion into visible radiation is poor. Filling gas in the discharge tube: The discharge tube is filled with a mixture of inert gases (neon and argon or krypton- argon), a dosis of mercury and appropriate halides, depending on the type of lamp. Filling gas of the blister: The blister of a metal halide lamp whose discharge tube is filled with a mixture of neon- argon, must also be filled with neon so that neon pressure inside and outside the tube is the same. In case the discharge tube is filled with a mixture of krypton- argon, nitrogen may be used in the blister, or else, the latter may be eliminated, too. Working conditions of metal halide lamps are very similar to those of conventional mercury vapor. They are prepared to be connected in series with a ballast to limit current, a compensation condenser being necessary. 104 LIGHTING ENGINEERING 2002

94 Chapter 8. LAMPS Due to metal halides, the ignition voltage for these lamps is high. The use of a starter or ignition device with shock voltage of 0.8 to 5 KV is needed. Most lamps allow for immediate re- ignition with hot lamps (right after being turned- off), by using shock voltage of 35 to 60 KV. If not, they must cool- down between four and fifteen minutes before being turned back on High pressure sodium discharge lamps This section deals with those lamps with a discharge tube where sodium vapor is introduced. Low pressure sodium lamps and high pressure sodium lamps are included Low pressure sodium lamps There exists a great similarity between the working of a low pressure sodium lamp and a low pressure mercury lamp (or a fluorescent one). However, while light in the latter is produced by transforming ultraviolet radiation of the mercury discharge into visible radiation, using fluorescent powder in the inner surface, visible radiation in the former is produced by direct discharge of sodium. Working principle The discharge tube of a low pressure sodium lamp is usually U- shaped and is located inside an empty tubular glass cover, with indio oxide coat on the inner surface. The empty part, together with the layer, which behaves as an infrared selective reflector, helps keep the discharge tube wall at an adequate working temperature. Such measurements are necessary for the sodium, which is deposited in slits of the glass when condensed, and it evaporates with a minimum heat loss. Due to this fact, the most luminous efficiency possible is achieved. The neon gas inside the lamp is used to begin the discharge and to develop enough heat to vaporize the sodium. This responds for the red- orangish luminescence during the firsts few working minutes. The metallic sodium is gradually evaporated, producing the characteristic monochromatic yellow light, with 589 nm. and nm. lines in the spectrum. The red colour, initially produced by the neon discharge, is energetically suppressed during the working because sodium excitation and ionization potentials are much lower than those of neon. The lamp reaches its luminous flux established in approximately ten minutes. It will re- ignite immediately in case power supply is momentarily interrupted, since vapor pressure is quite low and the voltage applied enough to reestablish the arc. The lamp has a luminous efficiency up to 200 lm/w and a long life. Therefore, this lamp is applied to those places where colour reproduction is of less importance and mainly where contrast recognition matters, for example: motorways, ports, beaches, etc. Low pressure sodium lamps range from 18 W to 180 W. LIGHTING ENGINEERING

95 Chapter 8. LAMPS Main parts Bayonet cap Deposit area for non vaporised sodium Clear blister bulb Double or triple spiral electrodes with electrone emission matter "U"- shaped discharge tube Figure 12. Low pressure sodium lamp. Discharge tube and supports: The discharge tube of a high pressure sodium lamp is U- shaped, to make the most out of space and provide a better thermal isolation. It is made out of sodium- calcium glass, and has an inner surface covered with borate glass to form a protective layer against sodium vapor. The tube also contains a number of small slits or holes, where sodium is deposited during manufacturing. Discharge tube filling: The discharge tube filling consists of metallic sodium of high purity and of a mixture of neon and argon, which behaves as an ignition and trimmer gas. Electrodes: Low pressure sodium lamps possess cold ignition electrodes. These consist of a triple wolfram wire, in such a way that a great amount of emitter material may be maintained. Blister: It is empty and covered by a thin film of infrared material reflector in its inner surface. The infrared reflector serves to reflect most part of the heat radiation which returns to the discharge tube, keeping it, at the desired temperature, this way, while visible radiation is transmitted. These lamps precise an auxiliary equipment formed by a power supplier with an autotransformer or ballast and igniter with impulse voltage depending on type. A compensation condenser is required. Nominal values are reached after fifteen minutes after re- ignition. When the lamp is turned off, a few minutes are necessary before re- ignition High pressure sodium lamps Physically speaking, high pressure sodium lamps are quite different from low pressure sodium lamps, due to the fact that vapor pressure is higher in the former. This pressure factor also causes many other differences between the two lamps, including emitted light properties. Discharge tube in a high pressure sodium lamp contains an excess of sodium to produce saturated vapor conditions when the lamp is working. Besides, it has an excess of mercury to provide a trimmer gas, xenon excluded, to ease ignition and limit heat conduction from the discharge arc to the tube wall. The discharge tube is housed in an empty glass cover. High pressure sodium lamps radiate energy through a good part of the visible spectrum. Therefore, when compared to the low pressure sodium lamp, they offer a quite acceptable colour reproduction. Main parts The main parts of a high pressure sodium lamp are the following: 106 LIGHTING ENGINEERING 2002

96 Chapter 8. LAMPS Clear blister bulb Base Discharge tube Diffused blister bulb Figure 13. High pressure sodium lamp. Discharge tube: The discharge tube is made out of aluminium oxide ceramics (sintered aluminium) very resistant to heat and to chemical reactions with sodium vapor. Electrodes: Electrodes, covered by a layer of emitter material, consist of a twisted serpentine wolfram rod around it. Filling: In the inside of the discharge tube are sodium, mercury and noble gases (xenon or argon) out of which sodium is the main producer of light. Blister: This glass is generally empty. The shape must be either ovoid or tubular. The first one has an inner covering. However, since the discharge tube of the high pressure sodium lamp does not virtually produce any ultraviolet radiation, the covering is simply a diffused layer of white powder, to decrease the high brightness of the discharge tube. The tubular glass is always made out of clear glass. Starters and auxiliary starters: Many of the high pressure sodium lamps have an incorporated auxiliary starter, which helps reduce the measure of the ignition peak voltage needed for the lamp ignition. Sometimes, both the incorporated starter and the auxiliary starter are in the lamp itself. These lamps precise of an auxiliary equipment formed by a ballast and an igniter with impulse tension depending on type. A compensation condenser is also needed. Nominal values are reached five minutes after ignition. When a lamp is turned off, due to a great pressure of the burner, it needs to cool down between four and minutes before turning it back on Induction lamps The most vulnerable parts of all discharge lamps are the electrodes. During their average rated life, lamps reduce and lose their emitting voltage by the impact of quick ions or by chemical reactions with energetic vapors in the discharge tube. Electrodes in high pressure discharge lamps also produce a great amount of infrared wasted radiation, which decreases efficiency of the lamp. The induction lamp introduces a completely new concept in light generation. It is based on the low pressure discharge gas principle. The main characteristic of the new lamp system is that it does not need electrodes to originate gas ionization. Currently, there are two different systems to produce this new ionization of gas without electrodes. LIGHTING ENGINEERING

97 Chapter 8. LAMPS High power fluorescent lamps without electrodes Discharge in this lamp does not begin and end in two electrodes like in a conventional fluorescent lamp. The shape of close ring of the glass of the lamp allows to have a discharge without electrodes, since energy is supplied from the outside by a magnetic field. Such magnetic field is produced in two ferrite rings, which constitutes an important advantage for lamp duration. Ferrite nucleus Magnetic field Fluorescent covering Coil Electron Mercury atom Ultraviolet radiation Visible light Figure 14. High voltage fluorescent lamp without electrodes. The system has an electronic equipment (at a frecuency of approximately 250 khz) separated from the lamp besides a fluorescent tube without electrodes. This allows to preserve optimal energy of discharge in the fluorescent lamp and reach a high luminous potency with a good efficacy. The main advantages of this lamp are: - Extremely long life: hours. - Lamp potency 100 and 150 W. - Luminous flux up to lumens. - Luminous efficacy of 80 lm/w. - Low geometric profile that allows the development of flat luminaires. - Comfortable light without oscillations. - Start without flickers or sparkles. These lamps are essentially indicated for those applications where relamping increases maintenance expenses excesively, like for example, illumination of tunnels, industrial premises with very high ceilings and difficult access, etc Low pressure gas discharge lamps by induction This type of lamps consists of a discharge recipient which contains the low pressure gas and a voltage coupler (antenna). Such a potency coupler, composed by a ferrite cylindrical nucleus, creates an electromagnetic field within the discharge recipient inducing an electrical current in the gas generating its ionization. Enough energy to begin and maintain discharge is supplied to the antenna by a high frequency generator (2.65 MHz) by means of a coaxial cable of a determined length, since it forms part of the oscillating circuit. 108 LIGHTING ENGINEERING 2002

98 Chapter 8. LAMPS Bulb Potency coupler Figure 15. Gas discharge lamp by induction. The main advantages of these lamps are: - Extremely long duration: hours. - Voltage lamps with 55, 85 and 165 W. - Luminous flux up to lumens. - Luminous efficacy between 65 and 81 lm/w. - Instantaneous ignition free of flickers and stroboscopic effects. - Light for a great visual comfort. These lamps are used for many general and special lighting applications, mainly to reduce maintenance expenses, like in public buildings, outdoor public lighting, industrial applications, etc Charts with characteristics Fluorescent lamps TL linear fluorescent Average rated life : hours Nominal Flux Performance Diametre Length Lamp holder R.I. Chromatic power φ (lm) Lm/W Ø in mm L in mm Ra degree G B G B G A G A G B G B G A G A G B G B G A G A LIGHTING ENGINEERING

99 Chapter 8. LAMPS Compact fluorescent TC-D of 2 pins Power supply voltage: 230 V. Average rated life: hours. Nominal Flux Performance Width Length Lamp holder R.I. Chromatic power φ (lm) Lm/W in mm L in mm Ra degree G24d B G24d B G24d B Compact fluorescent TC-D of 4 pins Power supply voltage: 230 V. Average rated life: hours. Nominal Flux Performance Width Length Lamp holder R.I. Chromatic power φ (lm) Lm/W in mm L in mm Ra degree G24q B G24q B G24q B Compact fluorescent TC-L of 4 pins Power supply voltage: 230 V. Average rated life: hours. Nominal Flux Performance Width Length Lamp holder R.I. Chromatic power φ (lm) Lm/W in mm L in mm Ra degree G A G A G A G A G A High pressure mercury lamps Average rated life: hours. Colour temperature: K K Colour reproduction index (R): 50 Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E E E E E LIGHTING ENGINEERING 2002

100 Chapter 8. LAMPS Blended light lamps Average rated life: hours. Colour temperature: K K Colour reproduction index (R): 50 Power suuply voltage: 230 V. Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E Metal halide lamps Average rated life: hours. Colour temperature: K K Colour reproduction index (R): Compact metal halide lamps Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm G G G12 Double- based metal halide lamps Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm RX7s RX7s Fc Fc Cable Cable Metal halide lamps with a clear base and a clear tubular shape Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E E E-40 LIGHTING ENGINEERING

101 Chapter 8. LAMPS Metal halide lamps with a base in an ellipsoidal form with a diffusing layer Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E E E Low pressure sodium lamps Average rated life: hours. Colour temperature: K Colour reproduction index (R): NULL. Low pressure sodium with a clear tubular shape and an infrared reflecting layer Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm BY-22d BY-22d BY-22d BY-22d BY-22d BY-22d Low pressure sodium with a light tubular shape Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm BY-22d BY-22d BY-22d BY-22d BY-22d 112 LIGHTING ENGINEERING 2002

102 Chapter 8. LAMPS High pressure sodium lamps Average rated life: hours. Colour temperature: K K Colour reproduction index (R): High pressure sodium lamps with a tubular shape Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E E E E E E-40 High pressure sodium lamps with an ellipsoidal shape and a diffusing layer Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E E E E E-40 High pressure sodium lamps with two bases Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm RX7s RX7s Fc Fc2 Luxurious high pressure sodium lamps with a tubular shape Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E-40 LIGHTING ENGINEERING

103 Chapter 8. LAMPS Luxurious high pressure sodium lamps with an ellipsoidal form and a diffusing layer Nominal Flux Performance Diametre Length Lamp holder power φ (lm) Lm/W Ø in mm L in mm E E E High powered fluorescent lamps without electrods (induction) Power supply voltage: 230 V. Average rated life: hours. Nominal Flux Performance Width Length Lamp holder R.I. Chromatic power φ (lm) Lm/W in mm L in mm Ra degree 100 W (840/835) 1 B 150 W (840/835) 1 B Low pressure discharge gas lamps by induction Power supply voltage: 230 V. Average rated life: hours. Nominal Flux Performance Diametre Height Lamp holder R.I. power φ (lm) Lm/W. in mm. in mm. Ra 55 W (840/830/827) 85 W (840/830/827) 165 W (840/830/827) 114 LIGHTING ENGINEERING 2002

104 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS 9.1. General remarks Ballasts Starters Capacitors Energy- saving equipments Control gears for different discharge lamps. Circuits LIGHTING ENGINEERING

105 116 LIGHTING ENGINEERING 2002

106 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS 9.1. General remarks The present chapter deals with auxiliary equipments lamps need for their correct functioning. The equipment to be installed depends on the type of lamp. Incandescent, halogene and blended light lamps may be connected directly to the power supply without the need for any kind of auxiliary equipment, or by means of a transformer. Due to their characteristics, intensity going through them and tension applied are proportional. Discharge lamps have the particularity that the ratio between the intensity going through them and the tension applied is not proportional. That is to say, the ratio power- current is not linear but negative. In other words, tension of the arc depends little on the current that goes through it. Depending on the tension applied, if the start takes place, intensity of the current may increase enormously until a destruction of the lamp takes place or current fluctuates without proportion with little power variations. Because of these reasons, it is necessary to use some current stabilizing device if a correct working is to be achieved. Discharge stabilization The most simple element that could be applied is a resistance. This solution is not recommendable for alternating current though, because the lamp illuminates virtually when the power applied to the whole reaches instantaneous values, higher than the power of the arc. This is translated into flickering of the lamp. Hence, this type of stabilization is almost exclusively used with continuous current. Another element that may be also applied to discharge stabilization is a condenser. This solution is not tolerated in a normal frequency of 50 Hz. (let alone for continuous current) because current of the lamp is greatly distorted when strong peaks of short duration are produced. The lamp will emit light intermittently and it will run out prematurely. However, this system may be used with higher frequency power supplies (above 300 Hz.). The advantage being greater luminous performance of the lamp. The most widely known element to stabilize discharge lamps in normal practice is formed by an inductive reactance which limits the intensity of the discharge current, quite efficiently, simply and economically. Current distortion produced in the lamp is tolerable and generally without flickering. Although it displaces the phase between the power of the lamp and the supply net, this may be easily corrected by means of condensers in parallel with the line. When power available in the line is not enough to allow lamp ignition, previous transformers or autotransformers may help. In order to simplify the set, the so called leakage autotransformers (also called dispersion autotransformers) are used, too. They incorporate the precise inductive reactance in their secondary body. Once an adequate leakage transformer is available, if a fluorescent lamp is to work that requires heating of its cathodes for ignition, a starter is introduced. Or it may not be necessary means of incorporating two new coils to the autotransformer for a correct heating. Parallel to the previous evolution, the condenser necessary to correct the power factor was used. An inductive reactance in series with a condenser constitutes an intensity regulator. By correctly using the elements with slight alterations of these, complex equipments are built. In them, the condenser in series with the secondary one of the transformer, and sometimes with the primary one, improves lamp stability when compared to strong power variations in the line. Besides, it simultaneously corrects the power factor and cos of the whole to a better value than if a simple condenser in parallel to the line is used. Discharge lamps auxiliary equipments Let us analyze in a general way, equipments usually used by discharge lamps for their correct working. At the end of the present chapter, some representative circuits of different discharge lamps will be shown. Fluorescent lamps A fluorescent lamp has negative resistance characteristics. Therefore, it must be operated as a whole with a limited current device (ballast) to avoid current leakage. The ballast, which has positive resistance characteristics, may be: - Resistive ballast: For continuous current. - Inductive ballast: It is the most widely spread ballast used for normal alternating current applications. - Electronic ballast: It is the most expensive, but it offers important advantages compared to the previous ones. Power factor correction is achieved by placing a condenser in parallel to the circuit of the lamp. Also using capacitive ballasts for LIGHTING ENGINEERING

107 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS half the lamps and inductive ballasts without compensation for the other half in circuits which contain several lamps. For lamp ignition some type of help is needed, due to the fact that the fluorescent lamp inner resistance when turned off is too cold to be turned on automatically when the power supply is applied to it. As far as ignition is concerned, fluorescent lamp circuits may be divided into three groups: - Circuits with preheated starter: Ignition is controlled by a conventional or electronic starter. - Circuits without preheated starter: These lamps may operate with two different types of circuit, instantaneous ignition (semi- resonant circuit) and quick ignition (non- resonant circuit). - Circuits with cold ignition: Specially designed for lamps provided with an inner band to ease immediate ignition without preheating and without a starter. High pressure mercury lamps Apart from the reactance, a start equipment is not necessary for mercury lamps. Compensated inductive ballasts may be used both in parallel compensation circuits and in compensation circuits in series. Both circuits take a condenser to compensate for the power factor. Metal halide lamps Working conditions for metal halide lamps are very similar to those of conventional mercury one., They are arranged in such a way that they may be connected in series with a current limiting ballast. Nevertheless, due to halides, power ignition of these lamps is high and need the use of a starter or igniter. The ballast to be connected to the metal halide lamp depends on its properties. For example, the so- called three band lamps use ballasts designed for high pressure mercury lamps, but rare earth lamps work better with ballasts of high pressure sodium lamps. Low pressure sodium lamps These lamps require an auxiliary equipment which may be: - Ballast, with or without a separate igniter: Due to the lamp low voltage, these may operate in comparatively simple circuits which consist, basically, in a ballast in series with the lamp and a starter in parallel. For the correction of the power factor, a condenser in parallel is used. - Transformer with a separate igniter: In this circuit power of the lamp is almost always constant for all its life. It consists in a ballast, a condenser in series for the correction of the power factor and an electronic igniter. High pressure sodium lamps As for metal halide lamps, high shock powers are necessary for ignition due to the high pressure to which the gas is kept. Thus, high pressure sodium lamps operate normally with a ballast and a starter. Some lamps have an incorporated starter, but most of them use an external ignition device. Mainly, there are two types of circuits, either with the starter connected in series or in parallel with the lamp: - Circuit with a starter in series: The starter is connected between the ballast and the lamp. - Circuit with a semi starter in parallel: The starter is connected to the lamp through the reactance. Correction of the power factor may be achieved through a condenser in the way of compensation in parallel in both circuits. Induction lamps Induction lamps are connected to the power supply through a high frequency generator, which is formed by a system of electronic circuits. The connection between the lamp and the generator is achieved through a coaxial cable which forms part of an oscillator circuit. Therefore, its length may not be modified. 118 LIGHTING ENGINEERING 2002

108 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS 9.2. Ballasts Introduction Reactances or ballasts are accessories to be used in combination with discharge lamps. As inductive, capacitive or resistive impedances, alone or in combination, they limit the current which circulates through them to the values required for an adequate working. Moreover, they supply power and ignition current required when necessary, and, in the case of quick start reactances, they also supply low power necessary for the heating of lamp cathodes. Given the characteristics offered for correct performance and working of the lamp, the most widely used are those of an inductive type. The combination of inductive- capacitive reactance is also used. Resistance and capacitive ones are not used alone since the first ones produce many losses, thus, providing low performance. The second ones provide a very low power in the lamp due to great deformation of the current wave originated by them. According to their installation principles, they may be classified into: - Independent reactance, which is covered by a special protection to work outside. - Reactance to be incorporated, which requires a secondary protection like a housing, a luminaire, etc Function of the reactance The reactance is a fundamental element in any discharge lamp lighting installation because lamps would not work without it. Given the great variety of lamps in the market, very different in type, size, colour, etc., adequate reactances to each of them are required, so that the precise parameters are supplied in each case and for each situation. That is to say, starting needs and, later on, normal operation ones are satisfactory. Generally speaking, functions covered by reactances are the following: - To provide cathode ignition or preheating current to achieve the initial emission of electrons in these. - Supply enough output power in the vacuum to arc the lamp. - Limit current in the lamp to adequate values for a correct working. - Control variations in the lamp current, as opposed to variations in power supply. This is known as having a good regulation Normative to be met by reactances Reactances certification Reactances must be manufactured according to corresponding national and international norms. As a consequence, the ones that have been tested and certified by different organisms, will have the organization symbol printed (Fig. 1.). AENOR SPAIN GERMANY IMQ-ITALY IRAM-ARGENTINA SLOVAQUIA Figure 1. Examples of certification brands of different organisms. CENELEC-AENOR Having such certifications allows these products to circulate around countries comprised by such brands. Reference norms Norms regulating security and functioning of reactances for high intensity discharge lamps are the following: LIGHTING ENGINEERING

109 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS UNE-EN 60922: UNE-EN 60923: ANSI C82.4: UNE-EN 60662: UNE-EN 61167: UNE-EN 60188: UNE-EN 60192: UNE-EN 60598: Reactances for discharge lamps (except for fluorescent tubular lamps). General and safety prescriptions. Reactances for discharge lamps (except for fluorescent tubular lamps). Working prescriptions. Reactances for high intensity discharge lamps and low pressure sodium lamps. High pressure sodium lamps. Metal halide lamps. High pressure mercury lamps. Low pressure sodium lamps. Luminaires. European directives In order to be able to use electric and electronic devices in the European Union, it is compulsory for them to have the mark "CE" which means European Conformity, and represents the compliance with the following European Directives to which lighting products are subjected: - Low Voltage Directive (LV) 73/23/EEC, in force since and applicable to all electric devices of nominal voltage from 50 to 1,000 V. in alternating current and from 75 to 1,500 V. in continuous current. - Electromagnetic Compatibility Directive (EMC) 89/366/EEC, in force since and applicable to all electric and electronic devices that may generate radio- interferences or be affected by perturbances generated by other devices in their surroundings. Reference norms For the Low Voltage Directive (LV), security norms on the product are compulsory. For those corresponding to Electromagnetic Compatibility (EMC), the following norms are applicable: UNE-EN : UNE-EN 55015: EN : EN 61547: Electromagnetic compatibility. General emission norm. Radioelectric perturbations of fluorescent lamps and luminaires. Perturbations of power supply systems. Harmonics. Luminaires for general applications. Immunity prescriptions. The applicable harmonic and immunity requeriments of radio- interference emission must be checked with the luminaire or in the installation where reactances are going to be used. Harmonics A harmonic is a perturbation introduced in the power supply by electric equipments. In lighting systems, energy is supposed to receive a unique frequency and to be constant. Frequency constancy in energy distributions is generally achieved. However, due to several circunstances, the fundamental wave may be polluted with undesirable harmonics (for example, produced by associated frequency converters, etc.). The study of such pollution produced by harmonics is very complex because its consequences depend on the harmonic frequency amplitude and order, as well as on the situation over the fundamental. 120 LIGHTING ENGINEERING 2002

110 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS It is necessary to highlight that if the situation of harmonics over the fundamental wave makes composed waves to tend to be square, impedance coils do not limit intensity received from the lamp sufficiently. Under these conditions, alternating voltage is similar to a continuous pulsatory voltage to which inductive shocks do not respond in an efficient way. A mathematical model may be established for the study of power in different elements of the electric circuit (lamp, ballast, etc.), and decompose it in Fourier s series, taking the first two terms as an acceptable approximation. The third and subsequent harmonics produced during the use of electromagnetic nuclei (magnetic ballasts) in lighting with discharge lamps and the generation of odd harmonics produced by the lamps themselves, have two immediate consequences: 1 st - Capacitors of power factor correction are not able to correct power factor down to the unit, but, on adding capacity to such condensers, a capacitive circuit appears. 2 nd - In threephasic systems with neuter, current in the neuter becomes similar to that of phases. The reason is that even cancelling the fundamental frequency charges being equal, that is to say, with balanced phases, the third harmonics are in phase and, therefore, they are summed. If devices providing power supply of the threephasic line with neuter would take only the fundamental frequency, the neuter would not carry current in case of charge balance over the phases. However, if devices take a current containing 33.3% of the third harmonic, the neuter wire is charged with the same current as that of the phases, although its frequency is three times the fundamental. In practice, so that this does not happen with lighting lines, limits have been established in admissible current distorsions for even harmonic cases, since odd numbers are cancelled (see IEC , IEC or EN and EN Norms). Nevertheless, the neuter must be measured at the same size than those of phases, as demanded by the Low Voltage Regulation, in order to avoid surprises with low quality materials. Another typical problem with power supply polluted by frequency harmonics is the resonance phenomenon, which may take place in those equipments composed by an inductive reactance and a condenser in series. These equipments are special and known as regulators, autorregulators or constant power ballasts Electromagnetic ballasts Electromagnetic ballasts are mainly composed by a large number of copper coils over a laminated iron nucleus. A heat loss takes place in them through the coil ohmic resistance and the hysteresis in the nucleus. This depends a lot on the mechanic construction of the ballasts and the copper wiring diametre. Types of reactances Shock reactance This type of inductive reactance, formed by a simple coil with its corresponding magnetic nucleus, electrically connected in series with the lamp, is the most comonly used. It constitutes a set of low factor power which may be corrected placing a condenser in parallel with the power supply (Fig. 2). Ballast F Power supply Capacitor N Lamp Figure 2 This type of reactance, economic, light and of a small size, provides poor power regulation, as opposed to variations in the power supply voltage (around 20% of the power oscillation, for power supply variations of 10%) and starting current is high with respect to the functioning; circuits must be measured for that value. This makes lamp life to be considerably reduced if LIGHTING ENGINEERING

111 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS power supply volatge fluctuates more than 5%. Therefore, this type of reactances is adequate whenever adequate voltage stability conditions are met. Autotransforming reactance When power supply has a voltage lower than 220 V, it is necessary to foresee an elevation system for that voltage which will provide us with the necessary one for lamp ignition. This system may be simply an autotransformer and a normal shock reactance, which is correct from an electric point of view, but also very costly and bulky. F Ballast Power supply Lamp N Figure 3 Normally, autotransforming reactances have been built for this function, whose basic structure is shown in Fig. 3. They are formed by two magnetically decoupled winded, even with magnetic shunts between them. So, on top of raising voltage so that the lamp may be ignited, they also control its intensity. This type of reactances have a very small power regulation. Thus, a voltage variation of about 5% is transformed into lamp power oscillations of 12%. Besides, we are speaking about power low factor reactances. In order to correct this factor, bearing in mind that power supply (normally 110 or 125 V), it is obligatory to place condensers with a great capacity, and, thus, very costly ones. Autorregulating reactance This reactance combines an autotransformer with a regulating circuit. Due to the fact that part of the main coil is common to the second one, its size is reduced. Since only the secondary coil contributes to a good regulation, its degree depends on the portion of primary power coupled to the second one (Fig. 4). Capacitor F Ballast Power supply Lamp N Figure LIGHTING ENGINEERING 2002

112 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS With this type of reactance, the following advantages are achieved: - A good regulation of current and power of the lamp, as opposed to power supply variations (about 5% in power, as opposed to voltage variations of about 10%). - As a consequence from the above, an important increase in lamp life, reducing installation maintenance expenses. - Power supply starting current is not higher than the normal functioning, so protection systems and power supply cables may be measured for a minor current than in installations with shock reactances. Due to the same reason, protection security increases since its values correspond to those of functioning. - Compensation of the power factor is maintained above 0.9 independently from the power supply current voltage. - Due to the great stabilization provided by these reactances, power supply voltage is low (at this power the lamp extinguishes). Power supply variations, very much above the usual ones, are permited without producing lamp turnoffs. Brands and indications Reactances, besides their electric characteristics, have a series of printed indications which is convenient to know to make good use of them. Thus, the maximum segurity, duration and electric performances are obtained. t W t It is the maximum temperature to which coils of a reactance may be constantly working in normal conditions, at their nominal voltage and frequency, to secure an average life of 10 years. Increases or decreases of temperature in coils have an influence on their life. Coil heating of a reactance over room temperature in which they are installed, working in normal conditions and at nominal voltage and frequency. t a Maximum room temperature at which a reactance may work in normal conditions. It is given by: t a = t W - t Losses It is the autoconsumed power. If not indicated otherwise, this value is measured with nominal voltage and frequency and with coils at a temperature of 25ºC. It is the power factor. Besides these, conformity prints from different organisms may appear as it was previously indicated Electronic ballasts Electronic ballasts offer important advantages with respect to conventional inductive ballasts, such as: - They improve lamp and system efficiency. - They do not produce flickering or stroboscopic effects. - They provide an instantaneous start without the need of a separate starter. - They increase lamp life. - They offer excellent possibilities to regulate the lamp luminous flux. - Power factor is close to the unit, although harmonics in line must be carefully observed so that maximum admited values are not exceeded. - Connection is simpler. - They have a smaller temperature increase. - They do produce neither a buzz nor other noises. - They are lighter. - They may be used in continuous current. Of course, these advantages correspond to electronic ballasts correctly designed, elaborated and verified. Electronic ballasts are generally used for fluorescent lamps metal halide and high pressure sodium lamps of up to 150 W. The most commonly used working principle in electronic ballasts for fluorescent tubes in normal alternating current connections (220 V and 50 Hz) is as shown in Fig. 5. LIGHTING ENGINEERING

113 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS F Power supply N Trimmer capacitor Electronic control Lamp Lamp Narrow filter Rectifier High frequency oscillator Lamp stabilizer Figure 5 As it may be seen, a narrow filter placed before reduces distorsion of the power supply current and avoids that high frequency signals are reflected in the power supply. Besides, the electronic circuit must be protected from fortuitous impulses which appear in 50 Hz alternating current. Once the alternating current has been modified, and with the help of the coupling condenser, high frequency generation in square wave is the following step, through two transistors, generally. This frequency must be higher than 20 KHz. to go over audible limits and achieve the greatest performance. Before applying high frequency to tubes, some solutions to limit current and ease ignition must be established. It is also necessary to provide the necessary solutions to avoid ballast deterioration at the end of the tube life, etc. Concepts associated to electronic ballasts Power factor: In electronic ballasts, the power factor is corrected and has a constant value very close to the unit, controlled at any time during its functioning by the power factor correction circuit. Protection against surges: In threephasic installations with the neuter incorrectly connected or interrupted, if there is an unbalance of charges, there is also an unbalance of voltages, originating surges in some phases. This may create working problems and deterioration of lamps and auxiliary equipments. Electronic ballasts are provided with a protection system against surges, avoiding problems which may be produced in circuits due to this reason. Current harmonics: A pure non sine wave is formed by a fundamental wave to which frequency waves multiple of the fundamental one are superimposed. These superimposed waves are called higher order harmonics, as previously seen. These harmonics are produced by elements with a non- linear behaviour, overloading power supply systems. They are frequently discarded because they become a source of perturbations for other devices in the same power supply system and reduce the power factor of the device affected by them. Electronic ballasts must include input filters in their circuits to limit and maintain the level of harmonics equal or under the EN Norm exigencies. Dispersion or stray currents: In order to reduce radio electric interferences filters which originate disperse currents or non acceptable for a good electric functioning of the equipments are used. Electronic ballasts incorporate interference suppression condensers with an earth connection for stray currents, with values always lower than 0.5 ma. This does not constitute a problem for protection equipments and circuit differentials. For a correct installation, it is always necessary to use the ballast earth terminal and connect it adequately. Radio electric interferences: Electronic equipments functioning under high frequencies emit or generate harmful radio electric interferences for the electric surrounding and devices related to it. These emission levels must be located under the limit tolerated by the EN Norm. Electronic ballasts are equipped with stages and filters which suppress radio electric interferences. Hence, their emission is always inferior to the maximum normalized limits. 124 LIGHTING ENGINEERING 2002

114 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS To maintain this low emission level of radio interferences, special attention must be paid to the installation wiring disposition, following recommendations for this purpose at any time. Normative to which high frequency ballasts must comply In order to offer the maximum functioning and security guarantees, electronic ballasts must be designed according to the latest European norms in order to achieve the following characteristics: - Being electronic, they must be totally noise- free. - Not to produce flickering during ignition. - Corrected stroboscopic effect. - Useful as emergency devices, admitting continuous current power supply. - To allow a wide margin of power supply voltage. - To have an automatic disconnection circuit as opposed to faulty or depleted lamps. - To incorporate harmonic filters to avoid that these are introduced in the power supply. Therefore, they must comply with or follow the norms established below: UNE-EN : Electromagnetic compatibility. General emission norm. UNE-EN 55015: Radio electric perturbations of fluorescent lamps and luminaires. EN : Perturbations of power supply systems. Harmonics. EN 60928: General and security prescriptions. EN 60929: Working prescriptions. UNE-EN : Electromagnetic compatibility. General immunity norm. Ignition through high frequency electronic equipments Ignition time for an electronic ballast is the necessary time to begin lamp ignition. Depending on this period of time, instantaneous ignition equipments (or cold ones) and ignition equipments with cathode preheating (or hot ones) will be distinguished. Instantaneous ignition electronic ballasts: They produce lamp ignition almost instantaneously. This ignition takes place with cold lamp cathodes, without a previous preheating. The use of these ballasts is recommended in installations where a limited number of daily ignitions is required, like offices, shopping precincts, banks, etc. Quick ignition electronic ballasts: These ballasts, as opposed to instantaneous ignition, have a short preheating time, of approximately 0.4 seconds. Preheating ignition electronic ballasts: These ballasts produce lamp ignition in an approximate time of two seconds. Previous to ignition, lamp cathodes are preheated by a initial current that goes through them, which originates a softer ignition, but not an instantaneous one. Nevertheless, in this type of installations, the life of the lamp subjected to frequent ignitions is much shorter than that of a lamp subjected to few ignitions and long periods of continuous working. HF generator for induction lamps: The HF generator provides the signal of high frequency (2.65 Mhz) to the antenna of the lamp to begin and maintain gas discharge. The generator electronic circuit system is inside a small metal box which protects from radio frequency interference and drives heat generated in the circuit Starters Mercury lamps have electrodes which allow starting with a low voltage, around 220 V. Therefore, no additional starting device is required. However, metal halide and high pressure sodium lamps need very high ignition voltage which may not be supplied by the reactance alone. Supplying this ignition power is the role of starters, which are also used for ignition of some low pressure sodium lamps. LIGHTING ENGINEERING

115 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Working principles They are based on the principle of taking advantage of energy stored in a condenser, which is discharged by means of an adequate shooting system in the primary coil of a transformer. Due to the brusque flux variation in its nucleus, a voltage impulse induced in the secondary one appears. Its peak value is very high and it is of a short duration. When superimposed to the power supply, it arcs the discharge tube. According to its working principle three different types of starters may be distinguished: independent starter, impulse transformer starter and independent starter from two wires. Besides this classification according to their working, starters may have a deactivation system inside that will interrupt their working if the lamp does not start in a period of time. These are called temporized starters. Independent starter or impulse superimposed starter (Starter in series) It works as shown in Fig. 6. The starter of the condenser is discharged by means of the shooting circuit on the spirals of the primary transformer, which amplifies the impulse at the adequate value. The impulse voltage depends exclusively on the starter itself. It is compatible with any shock reactance and it does not bear ignition impulses, whose value is high in many cases. Ballast Transformer F Capacitor Shooting circuit Lamp Power supply Capacitor Resistance Starter N Figure 6 Impulse transformer starter (semi parallel starter) It uses the reactance as an amplifier of the products by the starter and it works as shown in Fig. 7. The condenser of the starter is discharged by means of the shooting device between points 2 and 3 of the reactance. Together with an adequate proportion of spirals with regards to the total coil, it amplifies the impulse to the necessary value. The value of the impulses depends both on the starter itself as well as on the reactance used. Due to this reason, it is not always compatible with any combination of both. The reactance must have an intermediate feeding point and it must also be subjected to high peak power voltage produced for ignition. Ballast F Capacitor Lamp Power supply Capacitor Shooting circuit Resistance Stater N Figure LIGHTING ENGINEERING 2002

116 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Independent starter from two wires (parallel starter) It works as shown in Fig. 8. The energy stored in condenser C is returned towards the lamp by the intervention of the shooting circuit D, in the precise moment in which voltage reaches its maximum value. An impulse of a peak value between 2 and 4 times the instantaneous of the power supply, between 600 V and 1,200 V, is reached, but with a longer duration, and, therefore, of more energy than those obtained with other systems of starters. Ballast F Resistance Lamp Power supply Capacitor Starter Capacitor Shooting circuit N Figure 8 The may be only used for some metal halide lamps and low pressure sodium lamps of 35 W., which require voltage impulses relatively low but of a certain duration. Temporized starters These starters have an inner device, which after a time previously fixed for impulse production, deactivates its working. If the lamp does nor ignite due to exhaustion or failure, its stops subjecting all circuit to high voltage impulses. The starter is active again after the interruption of the power supply circuit voltage, although only for a short period of time (milliseconds). LIGHTING ENGINEERING

117 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Reference norms Norms applicable to starters are the following: EN 60926: Starters (except for effluves). General and security prescriptions. EN 60927: Starters (except for effluves). Working prescriptions. EN 60662: High pressure sodium lamps. EN 61167: Metal halide lamps. Recommendations for the use of starters In the first place, the adequate starter for the lamps to be installed must be chosen so that the necessary peak voltage is provided, the number of impulses required for lamp ignition and the charge capacity born by the cables to the lamp is admitted. Location must be carefully chosen so that there is always the minimum distance from the starter to the lamp. Thus, the capacity of cables is minimum, securing ignition. Such a capacity depends on the separation between cables and on their length. The conductor bearing the high voltage impulse, indicated in all starters, must be of an insulation for a voltage in service of no less than 1 KV., and be connected to the central contact of the base to favour its ignition. The connecting form indicated in the sketch of the starter must be always respected. Humidity, water or condensations in the housing of the starter must be avoided. Derivations between terminals or to earth may be produced, which would cancel the high voltage impulse, failing ignition. An excessive room temperature must also be avoided because it may provoke an overheating in the starter and risk its average life. Temperature at the point indicated on the surface of the starter must not exceed the value indicated for t C ºC, when the lamp is working and thermally stabilized. The starter produces voltages of up to 5 KV. Thus, insulation of cables supporting them must be especially considered. It is not advisable to work on the luminaire without being sure that power supply is off. Connect the condenser for the voltage correction factor to avoid impulse losses towards the power supply. Starters This name is given to starters designed for fluorescent lamp ignition. The most common type of starter is that called flicker, composed by a glass bulb full of neon gas at a low pressure. In its interior there are two electrodes, one of them or both are bimetal lamellae which bend slightly by the action of heat. In parallel with the electrodes, a condenser is connected to eliminate interferences. All this is housed in a cylindrical recipient made of aluminium or of an insulating material. A plaque with two pins for contact and fixing are included. The starter is embedded in series with the lamp electrodes and ballast, working automatically in the following way: When the connection is established, a small electric discharge takes place between the lamellae through the gas, heating them enough to bend till they get together. This union closes the circuit and eases the flow of current through the lamp electrodes for a short period of time. When the electrodes are incandescent, they emit electrons around them in the form of a cloud. A bit later, when the lamellae cool down, they separate opening the circuit and giving rise to the ballast spreading a power impulse tension through which discharge of the arc and lamp working takes place. Once the lamp is turned on, the starter is out of service without an insufficient voltage reaching it. If ignition fails, the starter behaves exactly in the same way. However, electronic starters only make one ignition attempt (very determined) so that any flickering during the ignition stage is eliminated. Additional advantages of electronic starters are high ignition reliability at low room temperatures and prolongation of lamp life. 128 LIGHTING ENGINEERING 2002

118 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS 9.4. Capacitors General remarks Electric capacitors are a system formed by two conductors separated by insulation. If no element is between the two conductors, air is the insulator. Nevertheless, generally speaking, air is substituted by another insulator with higher dielectric power. Hence, conductors (frameworks) may be very close to one another without electric charges jumping from one to the other. If frameworks of a capacitor are connected to the poles of an electric generator, equal and different sign charges are adquired. So, once it has been disconnected, the capacitor stores electric charges. The amount of charge stored by a capacitor is directly proportional to the power differential established between its plaques. But it may also happen that two capacitors of a different form or size adquire different charges when subjected to the same power difference. Capacity of a capacitor is the quotient between the charge of one of its plaques and the power differential between both of them. C = q U where: C = capacity of the capacitor. q = charge of the capacitor (coulomb). U = power differential between the capacitor (V) plaques or pins. Pure capacitive circuit Capacity (capacitance) of an electric circuit or of an element of the circuit serves the purpose of delaying a variation in the voltage applied between its terminals. That delay is caused by absorption or cession of energy and it is associated with the variation in the electricity charge. A pure capacitive circuit is that whose ohmic resistance equals zero (pure capacitance). Following the electric field laws, voltage between the plaques of a capacitor is known to be proportional to the stored charge and that the ratio q/u is the capacity. If instead of a continuous current, a capacitor is applied a sine alternating current, a variation of the same du will be necessary to produce another variation in the charge dq = i dt in an infinitesimal time dt. That is to say: dq = i dt = C du If a sine alternating voltage is applied to the circuit u = Umax sin ( t), and it is substituted in the previous equation, derivation and operation is as follows: i = U max C sin( t + ) 2 This equation indicates the advance suffered by the intensity with regards to voltage due to the capacitor effect. Frequency effect Capacity reactance The capacity of a circuit serves to delay the increase or decrease of voltage, but under no circumstances does it avoid or limit change. Nevertheless, frequency limits current amplitude in a value equal to 1 = 1 ohms. This value is called. C 2.. f. C capacitive reactance X C, which increases when frequency decreases and it decreases if frequency increases. Thus, for continuous current like f = 0 Hz, the capacitive reactance value is infinite and that of current is zero amperes. Inductive reactance Inductance of a circuit serves the purpose of delaying the increase or decrease of current, but under no circumstances does it avoid or limit the change. However, frequency limits amplitude of the current in a value equal to. L = 2.. f. L ohms. This LIGHTING ENGINEERING

119 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS value is known as inductive reactance X L, which increases when frequency is higher and decreases if frequency also does. Thus, in continuous current, like f = 0 Hz., the value of inductive reactance is zero. Resistance Resistance offered by a conductor in alternating current may be said to be the same as that offered in continuous current (ohmic resistance), whenever the Kelvin and corona effects, and resistance due to parasite currents, hysteresis, etc. may be disregarded. Generalized Ohm s law In circuits, the electric current is limited by the resistance value (R), the inductive reactance (X L ) and the capacitive reactance (X C ) of the elements forming the circuit. All these elements may undergo a sine alternating voltage which, as a permanent regime, makes an alternating intensity current circulate in the same form and wave frequency. Also, generalized Ohm s law for alternating current is verified in them. The formula is as follows: Z r = r Ur I ( ) Z r = Z. (cos + j. sin ) = R + j. X ( ) The real part of the complex number is the measurement known as resistance, R, represented in the real axis. Its module equals: R= Z. cos = ZZ2 - R 2 ( ) The imaginary part of this complex number, Z r is the reactance X, represented in the imaginary axis in such a way that if it is of an inductive nature, it is positive, +j. X L, and if it is of a capacitive nature, it is negative,-j. X C. Its module equals: X= Z. sin = ZZ2 - R 2 ( ) The angle is the phase different angle between tension and intensity, in such a way that if it is positive, it corresponds to an inductive circuit. If it is negative, it corresponds to a capacitive circuit. As it is widely known, this angle is of great importance in alternating current. It is called power factor and provides information about reactive energy and also quantifies it. XL Z ϕ -Xc X (inductive) 0 R Figure 9 If the impedance triangle of Fig. 9 is multiplied by I 2, the result obtained is its corresponding power triangle, in which: Active power P = R. I 2 = U. I. cos (W) Reactive power Q = X. I 2 = U. I. sin (V Ar) Apparent power S = Z. I 2 = U. I (V A) 130 LIGHTING ENGINEERING 2002

120 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS S Q ϕ 0 P Figure Power factor Power factor (cos ) may be defined as relative efficiency in the use of electric energy. Technically speaking, it is the ratio between active power P (in W.) submitted to a receptor and apparent power S (in V.A.) supplied by the power line. S=UI= P 2 +Q L 2 ϕ Q L =UI sinϕ 0 P=UI cosϕ Figure 11 It will always be lower than the unit, but the closer to it, the more advantage we are taking out of the energy from the power supply. Norms for reactances specify that an equipment (set of reactance lamp) has a high power factor when its value is equal or greater than The use of high power factor reactances has the following advantages: 1- Compliance with requisites from electric energy supply companies of compensating the power factor, at least, at To avoid extra charges in light bills for reactive energy. 3- To reduce the section in power supply line conductors in installations. 4- To use high power factor equipments implies to install a larger number of luminaires per circuit so that protection equipments are reduced and simplified (magnetothermal, differentials, etc.). Power factor compensation As usual, industrial use reactances are of an inductive type and their power factor is around 0.5. Reactances of a capacitive type must be associated to them so that the power factor of the set is close to the unit. This capacitive reactance consists in one or several capacitors, whose installation is convenient near the inductive reactance in order to measure conductors for the smallest intensity possible. This would not be achieved if capacitors are placed at the beginning of the installation, next to the distribution board, for example. On selecting the necessary compensation method, location of capacitors and economic aspects should be considered (prices, power supply parameters, acquisition initial expenses and equipment maintenance expenses). Apart from this, there are factors such as system harmonics and surrounding conditions which may limit the effective use of capacitors. There is not a compensation method which may be universally recommended. Nevertheless, several methods may be applied in each case. LIGHTING ENGINEERING

121 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Compensation in parallel Compensation in parallel is done as shown in Fig. 12 where a fluorescent lamp with ignition through a starter has been represented as a typical example, but it may be applied to any other type of lamp. I γ I L Ballast F I c Power supply Capacitor Lamp Starter N I L Figure 12 The capacitor connected in parallel to the power supply, must have the adequate value so that reactive intensity ahead of the phase absorbed by it, I C, formed by the one circulating through the lamp, I L, gives a power supply absorbed intensity, I T, whose power factor is close to the unit (Fig. 13). I c I t ϕ' Vpower supply I L ϕ Figure 13 Power to be born by the capacitor is that of the power supply, and tolerance admitted in capacity is usually ±10% of its nominal value. Being: V POWER SUPPLY = Power supply tension. I L = Current absorbed by the equipment without compensation. I C = Current absorbed by the capacitor. I t = Current in power supply after compensation. and =Phase difference angles after and before compensation. Calculation of the necessary capacitor Calculation of capacity (C) of the necessary capacitor in an equipment may be solved with the help of the following formula: where: C = P. (tag - tag ) (F). V LIGHTING ENGINEERING 2002

122 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS cos = cos = V = = initial power factor. ( = arc cos ). power factor to be achieved. ( = arc cos ). power supply of the line. frequency in radians. ( = 2.. F; F is the frequency in Hz.). Compensation in series As established before, compensation in parallel reduces the reactive power component of the power supply, and, thus, power losses. With compensation in series reactive power is transmitted to a certain degree and the recover of the line remains influenced when connecting capacitors in series to the power supply. The formula for the power loss in the line is given by: U = I a. R + Ir. (XL - X C ) This formula shows that, when X C = X L,, the power supply reactance is zero and the tension loss originated by the reactive power transmission is also zero, as a consequence. When an adequate capacitor in series, is included, X c may be greater than X L. In this case, reactance of the power supply becomes negative. Thus, compensation in series may also reduce a power supply drop caused by the transmission of active power Energy- saving equipments In public lighting through discharge lamps, energy consumption may be reduced during early hours or in circumstances which require less visual exigency by means of a reduction in illuminance for each point or in most of the corresponding luminous points. In old installations, two lamps used to be mounted on each luminaire for road lighting so that two lighting levels were available depending on conveniences. Nowadays, one luminaire with a single discharge lamp incorporated and with double level equipment is used. This ballast allows a reduction of consumed power by means of the introduction of an additional inductance incorporated to the iron nucleus of the main inductance in a separate nucleus in the lamp circuit. Figs. 14, 15 and 16 show three forms known of the double level system referred to a vapor mercury lamp. Relay Double level ballast Lamp F N Figure 14. The relay switches the winding intake in a single nucleus. LIGHTING ENGINEERING

123 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Relay F Principal ballast Auxiliary ballast Lamp N Figure 15. The relay is inserted in series with the auxiliary shock circuit. Relay Auxiliary ballast Lamp F Principal ballast N Figure 16. The relay opens the shock circuit derived from the main one. In any case, lamp consumption is reduced since the relay acts, connecting with an important line existing in the installation. Also, a temporizer in the equipment of each luminaire may be available, which programmed as required, passes from the normal level to the reduced one. The double level system being described may be applied to high pressure mercury lamps and high pressure sodium lamps (having special care in ignition circuits). This system is not adequate for metal halide lamps because the colour of the light is very much affected by the emitted power. In energy saving systems with several lighting levels, the power factor of the installation must be carefully watched. Sometimes it will be necessary to reduce the needed installed capacity for the maximum level in the minimum level. An added advantage in double level equipments is the longer duration of equipments and lamps, since generally, harmful surges are produced in lines during hours in which lighting is connected at a reduced level Control gears for different discharge lamps. Circuits Fluorescent tubes Fluorescent tubes are classified into two large groups, depending on whether cathodes are heated or not for ignition. The most common ones are the hot cathode that may be ignited by means of a thermal starter (Fig. 17), heating of filaments in the rapid ignition systems "rapid start" (Fig. 18), "trigger" ignition (the filament voltage is reduced once the tube has ignited), semi- resonant ignition (Fig. 19) and ignition through electronic means. 134 LIGHTING ENGINEERING 2002

124 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Another type of tubes is that of cold cathodes, which almost exclusively ignite through tension applied between their extremes. Ballast F Power supply Capacitor Lamp Starter N Figure 17. Ignition through starter. Inductive ballast. Compensation of power factor in parallel with the line. Lamp F Power supply N Capacitor Figure 18. Rapid ignition. Circuit with autotransformer dispersion (with heating of electrodes in parallel). F Ballast Power supply Capacitor Lamp N Figure 19. Rapid ignition. "Semi resonant" circuit with heating of electrodes in series. High pressure mercury lamps Electric equipments most commonly used are those with an inductance in series with the lamp limiting ignition and normal regime intensities. The low power factor produced by the use of the inductance is corrected using capacitors in parallel with the line (Fig. 20). When voltage of the line is insufficient or excessively large for the one requiring lamps, a transformer between the line and the stabilization inductance is coupled (inductance may be incorporated to the second transformer and it is then called dispersion or stray transformer). LIGHTING ENGINEERING

125 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Ballast F Power supply Capacitor N Lamp Figure 20. High pressure mercury lamp connection scheme. Low pressure sodium lamps Equipments used for this lamp type in the recent past have been almost exclusively constituted by a high impedance autotransformer in the second one and a capacitor in parallel with the line to improve the power factor (Fig. 21). Recently, inductances in series or semiresonant circuits (low voltages, Fig. 22) and hybrid circuits constituted by more complex autotransformers associated to electronic starters (Fig. 23) are used with new lamps in order to improve lamp performance and reduce power consumption strongly. Ballast Lamp F Power supply Capacitor N Figure 21. Dispersion autotransfomer. Reactance F Power supply Capacitor N Figure 22. Semiresonant starter. 136 LIGHTING ENGINEERING 2002

126 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Ballast F Power supply Capacitor Starter N Figure 23. Hybrid circuit. Electronic impedance and starter. High pressure sodium lamps For ignition of this type of lamps, electronic starters have been developed, which generate impulses lamps need for arc ignition in combination with the ballast, or independently. These starters must stop in impulse emission once the lamp is ignited, in order not to damage it. There are two types of starters from the point of view of their association with the ballast: the ones which incorporate a transformer for generation of high voltage impulses (Fig. 24) and those using inductance as a transformer (Fig. 25). The first ones must be mounted very close to the associated lamp; the ballast may be also located far from the lamp. Those which use impedance as a transformer are more economical and must harmonize the couple reactance- starter. The lamp may be far from the equipment depending on the cable capacity allowed by the starter. Anyway, stabilization in these lamps is strongly determined by the characteristic of the sodium arc, whose tension is not constant along its life. The best stabilization system for this type of lamp is an inductance in series with constant power supply. F Ballast Lamp Power supply Capacitor Starter N Figure 24. Scheme with an independent starter. Ballast F Power supply Capacitor Starter Lamp N Figure 25. Scheme with a semiparallel starter. LIGHTING ENGINEERING

127 Chapter 9. CONTROL AND REGULATION AUXILIARY EQUIPMENTS Metal halide lamps In general, special ballasts need not have developed for these lamps. Metal halide lamps with three bands use ballasts designed for high pressure mercury lamps. Rare earth lamps and tin lamps work well with ballasts for high pressure sodium lamps. Since the voltage of the ballast is not enough to start this lamp, an external starter is needed (Figs. 26., 27. and 28.) F Ballast Lamp Power supply Capacitor Starter N Figure 26. Scheme with an independent starter. Ballast F Power supply Capacitor Starter Lamp N Figure 27. Scheme with a semiparallel starter. Ballast F Power supply Capacitor Starter Lamp N Figure 28. Scheme with a parallel starter. 138 LIGHTING ENGINEERING 2002

128 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING General remarks Lighting levels Glare Shadows and modelling Light quality Lighting design Indoor lighting calculations Some recommended lighting levels LIGHTING ENGINEERING

129 140 LIGHTING ENGINEERING 2002

130 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING General remarks Human beings need to be informed about their surroundings in order to perform their activities in an easy and harmless fashion. Most information about the environment reaches human beings through their eyes. Therefore, it is of a visual nature. The term visibility (of an object) is used as a measure of easiness, fastness and precision an object may be detected and visually recognized. In consequence, a good visibility of the surrounding environment, and everything it contains, is essential. Good lighting is required for good visibility. Although good visibility of relevant objects is a necessary condition, it is not always enough to perform activities easily and comfortably. In indoor areas, where a task is performed, the main function of lighting is to provide comfort for visual tasks in this place. However, in circulation areas, resting areas or living rooms, visual capacity criterion is not so important. Pleasantness and visual comfort is what matters. Thus, the most important criteria related to lighting design for a particular application are visibility and visual satisfaction. Moreover, such factors must be well balanced in relation to installation and working costs Visibility / visual performance Working in indoor areas, the influence of lighting while doing the job is very important. Performance for a specific person, for a concrete job, is esencially translated into a function of the person s ability to perform a task (execution potential), on the one hand. On the other hand, the person s attitude towards the task execution (execution attitude) is also relevant. Attitude during execution determines, to what extent, the execution potential is efficiently used. It includes factors such as motivation, dedication and concentration, of a social or psychological nature, and which lie outside our field of study. Lighting, as well as other factors in the physic environment, may influence the execution potential, but, influence on real execution also depends on the execution attitude. Visual performance is the term used to describe the eye working speed and the accuracy with which a task is performed. Visibility of a task is generally determined by visibility of the most difficult element which must be detected or recognized so that work can be performed. This detail is known as critical detail. Visibility of the critical detail is a function of the difficulty experienced in order to discriminate it visually from the background on which it is seen, from other details found in its most immediate surroundings. Luminance In order to achieve good visibility at work, the most important factor is related to luminance of the task and its surroundings. The general effect of luminance on visibility is due to the resulting adaptation, process by which properties of the visual system are modified according to luminances of the visual field. For a given luminance distribution in the visual field, the adaptation process reaches a final state expressed as adaptation luminance. Visual system properties affected by adaptation to luminance are the following: - Visual sharpness, which is the capacity of the system to discriminate between details or objects that are very close. - Sensitivity to contrast, which is the capacity of the system to distinguish between small differences of relative luminance. - Efficiency of eye motor functions for accommodation, convergence, pupil contraction, eye movements, etc. Visual sharpness, sensitivity to contrast and efficiency of eye motor functions are larger with the increase of adaptation luminance up to a maximum certain level. For tasks where detail angular size is critical with respect to working visibility, an increase in visual sharpness due to another increase in luminance is highly important to improve task visibility. However, when the angular size of the critical size is very much above the threshold of visual sharpness, contribution to its increase is insignificant. Something similar happens with the above mentioned factors. They may also be positively affected by an increase in luminance. However, it will provide an improved visibility at work as a result, as long as such factors are critical with respect to visibility of the task under consideration. Diffusing objects and their surroundings Luminance of a matte surface is proportional to the product of illuminance in the surface and its reflectance. Luminance as a factor that influences visibility may be, in consequence, substituted by illuminance and reflectances for diffusing surfaces LIGHTING ENGINEERING

131 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING and their surroundings. Reflectances form part of the intrinsic properties of the task and the indoor area. These are not affected by lighting. Thus, for these tasks only illuminance remains a factor of the lighting system which affects visibility. It should be born in mind that for these tasks, luminance contrast is not affected by illuminance, but it is determined by reflectances of details and their background. Therefore, task visibility will be larger with the increase in illuminance up to a maximum certain level. The effect of the illuminance increase over visibility will be larger as size is smaller, or the contrast detail or the number of exigencies of the eye motor functions. For details of large angular size, with a high contrast with the background and static in a known position, the effect of illuminance increase in visibility on a moderate level will be insignificant. Bright objects and their surroundings Considering that luminance of a perfectly matt object is proportional to the product of illuminance and reflectance (diffuse), luminance of a regular reflecting surface is proportional to the product of its reflectance (regular) and the environmental luminance in the reflection direction. In practice, however, most surfaces do not belong either to the perfectly diffused reflection or to the perfectly regular one. Surfaces have mixed reflection properties in such a way that their luminance depends both on the illuminance properties of the surface as well as on the luminances of the surroundings. In order to relate luminance of mixed reflection surfaces with illuminance in a similar way as luminance of a matt surface is related to illuminance by its reflectance, the luminance factor has been introduced. Luminance factor of a surface in a given direction under certain lighting conditions, is the reason for the surface luminance in that direction to the luminance of a perfectly diffusing white surface, when they are identically illuminated. From this definition, it may be deduced that the luminance factor of a perfectly diffusing surface is constant and equal to its reflectance in all directions and under all lighting conditions. In an environment of uniform luminance L, luminance of a perfectly regular reflecting surface is L in all directions and luminance of a perfect diffusing white surface is also equal to L. Luminance factors of that regular reflecting surface under such lighting conditions, are equal to 1 in all directions. In an environment of luminance equal to 0 except for a limited L luminance area (source), luminance of a perfect diffusing white surface is smaller than L because illuminance is lower than illuminance in an environment of uniform luminance L. Luminance of a regular perfectly reflecting surface is equal to 0 except in all reflection directions of the source in which luminance is equal to L. Luminance factor of such regular surface, thus, is larger than 1 in the directions of reflection of the source and 0 in all other directions. Since bright surfaces have reflection properties partly regular and partly diffused, it may be deduced from all the above that for such mixed reflection surfaces, luminance factor will be constant and equal to its reflectance (mixed) in all directions only in a uniform luminance environment. In other environments, it may reach values between 0 and above 1, depending both on reflection properties and lighting systems. This also means that contrasts in objects which are not perfectly matt are affected by lighting because they are determined by luminance factors of details and background. These may reach different values in different visual directions, especially in directions of high luminance reflection. In conclusion, for tasks and bright contours not only illuminance is important for good visibility but also lighting direction. This is a general term which describes the special distribution of incident light in the task. It is determined by luminance distribution of the environment and depends on factors such as geometry of installation, luminances of luminaires and indoor reflectances Visual satisfaction Visual satisfaction is a term used to describe visual condition acceptability. For indoor work, visual satisfaction is essentially a function of easiness of work under real conditions, and pleasant or comfortable visual environment, when both concentrate on the task and when they are improved or seek relaxation. Visual satisfaction is affected by the luminous environment and individual preferences. For indoor areas with matt surfaces and tasks, influential factors of the luminous environment are illuminances in different 142 LIGHTING ENGINEERING 2002

132 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING surfaces and their task. Give origin to brightness by reflectio is. an important factor affecting visual satisfaction. For indor areas with bright tasks or surroundings, environmental luminances reflected on surfaces and which may veil the contrast of the task or give origin to brightness by reflection, are an important factor affecting visual satisfaction. Much research has been conducted in order to determine a preferred range of horizontal illuminances surrounding indoor areas. For such a purpose, carefully controlled values of surface reflectance in a room must be taken into account. Out of the results obtained in Western Europe, for brightness free fluorescent lighting conditions, an average curve has been determined indicating the percentage of observers which consider a particular illuminance as satisfactory. This curve is shown in Fig. 1, together with the evaluation of too dark and too light. % Too dark Satisfactory Too light (Lx) Figure 1. Response combinations Visual capacity Visual capacities vary from one individual to another, as it happens with other individual factors characteristic of people. Visual capacity depends on factors such as shape and transparency of elements of the eye optical system, accommodation capacity, convergence and aligning of eyes and retina spectral sensitivity. Reduced visual capacity due to refraction errors may be corrected using prescription glasses. Visual capacities are reduced with aging. The most important change when the eye ages is that the range on which it is possible to adjust accommodation exactly at a given distance is reduced. Other physical changes in the aging eyes are a reduction of light transmission by means of optical media and an increase in media dispersion. This means that old people may be less sensitive to central light, which may reduce visibility, and more sensitive to peripheryl light, which may cause glares. Providing a glare free adequate lighting is even more important for elder workers than for young people Lighting parameters Level and quality of lighting provided by a given installation may be described by means of the following parameters: - Lighting level. - Glares. - Shadows and modelling. - Quality of light. - Lighting design. LIGHTING ENGINEERING

133 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Lighting levels The required lighting level in a certain situation is expressed in terms of illuminance. At the end of this chapter some charts are shown where such a level may be consulted for most of the activities. Reference surface Reference surface of an indoor area is the surface where the recommended appropriate illuminance is supplied, selected from the charts shown at the end of the present chapter. The reference surface does not need to be reduced to a single surface area, but it may include a number of separate areas. Indoor lighting specifications must always include a clear definition of the reference surface. In indoor working areas, the reference surface will normally be the working plane. For indoor areas where tasks are not restricted to fixed places, the working plane is considered to be the horizontal plane limited by indoor walls at a height of 0.85 m. above the floor. For indoor areas where task localizations are known and clearly specified, the reference surface may consist in specific areas of working or task areas. When the task is not performed in a horizontal plane or is at a different height, the reference surface will have the angle of the task plane and be at its height. In indoor areas where work is not done, the reference surface may be the floor, the wall, or any important plane. Illuminance uniformity Illuminance given on the reference surface by a lighting installation will never be totally uniform, either in space or in time. Uniformity in space Measurement of illuminance uniformity on the reference surface is the ratio between minimum illuminance and average illuminance. In general lighting, illuminance uniformity on the reference surface must not be lower than 0.8 to provide possible locations of equivalent tasks in all the indoor areas. In localized general lighting or lighting of general areas, average illuminance in areas surrounding tasks must not be lower than one third of the level for task areas. Ratio between average illuminances for two adjacent indoor areas (for example, an office and a corridor) must not exceed 5:1. Uniformity in time Average illuminance given by an installation will gradually decrease with time due to depreciation of the lamp luminous flux and the accumulation of dirtiness in lamps, luminaires and surfaces in the room. Initial lighting: it is the average illuminance when the installation is new and surfaces in the room are clean. Initial illuminance must be chosen according to requisites imposed by the maintenance program. Its value should not be used for illuminance recommendations. Illuminance in service: it is the average illuminance during all maintenance cycle on the reference surface. In some countries, it is used for illuminance recommendations. Maintenance illuminance: it is the average illuminance on the reference surface during all the time between two maintenance operations, substitution of lamps and/ or cleaning of luminaires and surfaces in the room. In some countries, it is used for illuminance recommendations. In countries where recommended illuminance is established in terms of illuminance in service, maintenance illuminance should not be under 0.8 of the recommended value Glare Glare is the sensation produced by an exaggerated luminance within the visual field which alters sensitivity of the eye, causing discomfort, reducing visibility or both. Glare may take place in two different ways. Sometimes they occur separately, but generally, they take place simultaneously. The first is 144 LIGHTING ENGINEERING 2002

134 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING known as physiological glare (or disability glare). It impairs visual capacity and visibility, but it does not necessarily produce discomfort. The second is known as psychological glare (or discomfort glare). This type is discomforting but it does not necessarily impairs object observation. In indoor lighting, psychological glare (discomfort) is likely to be more of a problem than physiological glare (disability). Measurements taken to control discomfort glare will have to take discomfot glare into account, too. The sensation of discomfort experimented by discomfort glare tends to increase with the passing of time and contributes to nervous tension and fatigue. Any given type of glare may be direct or by reflection. Direct glare is the glare directly caused by luminances of the sources of light, such as lamps, luminaires and windows, which appear in the observer s field of vision. Glare by reflection is the glare produced by reflected luminances from surfaces with high reflectance, especially specular surfaces such as polished metals, except when these form part of the luminaire. Glare by reflection must be distinguished from other types of reflection which produce a reduction of the task contrast. They are more correctly described as veiling reflections (high luminance is reflected by the task towards the eyes, veiling it and reducing its contrasts) Glare control Control of direct glare of lamps and luminaires consists in controlling their luminance in the direction of the observer s eyes. Nevertheless, the degree of experimented glare is not only a function of luminaires in the worker s visual field, but it also depends on the type of activity performed. The more light demanded by the visual task, and the higher the need of concentration, the higher discomfort will be, too. However, in those situations where the worker must move to perform the task, the experimented discomfort will be less. Therefore, the luminance degree of control will differ according to the type of task or activity. The C.I.E. has classified tasks and activities in five groups depending on the required luminance degree of control. In Chart 1, five groups referring to Quality Classes are enumerated. In general terms, the highest luminances in an indoor area produced by the lighting installation are those coming from lamps. Generally speaking, such luminances are too high to use lamps without controlling their brightness in the direction of the eyes. This is the reason why one of the luminaire functions is to limit luminance in the critical directions at an acceptable level. Quality Glare Type of task or Class index (G) activity A, very high quality 1.15 Visual tasks exceptionally difficult. B, high quality 1.50 Visual tasks extremely difficult. Tasks requiring moderate visual demand and high concentration. C, average quality 1.85 Visual tasks moderately difficult, moderate concentration requirement and workers movement to a certain extent. D, low quality 2.20 Visual tasks demanding low visual and concentration levels, workers frequently confined to movement within a restricted area. E, very low quality 2.55 Interiors used with visual tasks not requiring a perception of detail where workers are not confined to a specific work place but they move freely from one place to another and not continuously used by the same workers. Chart 1. C.I.E. quality classes for glare limitation Practical methods for glare control Fundamentally, glare control means control of the focus luminance in the interval between 45º and 90º (Fig. 6). There are several methods to perform this control. Among them, two are going to be studied below, devoting more attention to the last one in section : LIGHTING ENGINEERING

135 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING -Control with translucent materials. - C.I.E. design system. Control with translucent materials This method controls visible luminance surrounding lamps with a diffuser or prismatic material. Usually, the strictest limits are imposed in the upper part of the interval. Luminaire mounting height, room dimensions, degree of control of selected glare and in some cases, luminaire orientation, notably influence the selection of appropriate limits for each interval. These factors have been born in mind for different systems developed in order to determine the appropriate luminance limit and/ or the degree of glare a determined installation is supposed to have. C.I.E. design system One of the main objectives of the C.I.E. on discomfort glare has been to develop a mathematical formula which may generate glare values for simple sources as well as for a group of sources. The formula proposed is the mathematical average term more usually applicable between different national systems. This formula is suggested to be rigurously checked bearing in mind its possible adoption as a formula recommended by the C.I.E E d / 500. w G= 8 loge. E i + E d L2 p R 2 where: G: C.I.E. glare index. E d and E i : vertical illuminances in the eye. E d : directly from sources of glare. E i : indirectly from background. L: luminance of the source of glare. w: size of the source of glare. p: Guth s position index (position index for each luminaire, which is related to the shift of the area of vision) C.I.E. glare protection system It is the system of luminance curve used in combination with a system of protective angle as an additional verifier for luminaires having visible lamps, or parts of them, within the zone of critical vision. It is considered to be the simplest and most practical method, and it is the one that will be described below. Luminance limitation curves (Fig. 2), comprise a scale of glare indexes which represent quality classes from A to E, together with different values of standard illuminance in service. Two diagrams depending on luminaire type and orientation according to the direction of vision must be used. 85 GM G Quality Values E illuminance in service (lx) 1.15 A =< B =< C =< D =< E =<300 a b c d e f g h a b c d e f g h 85 GM ab c d e f g h Cd/m Diagram 2 L Cd/m Diagram 1 L 2 3 Figure 2. Diagrams of luminance curves for evaluation of direct glare. 146 LIGHTING ENGINEERING 2002

136 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Diagrams of Fig. 2 are diagrams of luminance curves for the evaluation of direct glare. Diagram 1 is for those directions of vision parallel to the longitudinal axis of any elongated luminaire and for luminaires lacking lateral luminous panels observed from any direction. Diagram 2 is for those directions of vision in right angles to the longitudinal axis of any luminaire with lateral luminous panels. Limitation of the required luminance depends on the type and orientation of the luminaire, the shielding angle, the acceptance degree or quality class, and the value of illuminance in service. Type of luminaire The terms luminous laterals and elongated used to describe the types of luminaire are defined in the following way: - Luminous laterals: a luminaire is considered to have luminous laterals if it has a luminous lateral panel with a height of more than 30 mm. - Elongated: a luminaire is considered to be elongated when the ratio between the length and the width of the luminous area is higher than 2:1. Luminaire orientation When using diagrams in Fig. 2, luminance distribution of the luminaire in two vertical planes must be taken into account: the C 0 -C 180 plane and the C 90 -C 270 plane γ γ C 90 - C 270 C 0 - C 180 Figure 3. C- planes in which luminaire luminance must be verified. When luminaires are mounted in the C 0 -C 180 plane parallel to the axis of the premises, luminaire distribution on such a plane is used to control glare limitation in the longitudinal direction of the room. Luminance distribution in the C 90 -C 270 plane is used to verify glare limitation in the transverse direction of the room. When luminaires are mounted on the C 90 -C 270 plane parallel to the premises logitudinal axis, such a plane must be used to verify glare limitation in the room longitudinal direction, and luminance distribution on the C 0 -C 180 plane to verify glare limitation on the room transverse way. For elongated luminaires on the C 90 -C 270 plane this is chosen coincident with (or parallel to) the longitudinal axis of the lamp/ s. When such a plane is parallel to the direction of perceived vision, vision is supposed to be longitudinal. However, when the C 90 -C 270 plane is in right angles to the direction of vision, vision is considered to be transversal. Shielding angle For those luminaires which, when being observed from an angle of 45º or more with respect to the vertical, lamps or parts of them may be seen, not only the average luminance of the luminaire according to curves must be limited in Fig. 4, but also lamps must be well shielded depending on lamp luminance and quality class chosen. The required shielding angles (Figs. 4 and 5) are shown in Chart 2. If the shielding angle is equal or higher than the tabulated, glare will belong to the specified class or better.0 LIGHTING ENGINEERING

137 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING α α α Figure 4. Shielding angles for several luminaires. α Shielding angle 90 - γ < S 90 - γ = S 90 - γ > S Figure 5. Glare control due to shielding. Types of sources According to statistical experience, the minimum luminance threshold is that of 10-5 cd/m 2. Glare appears from cd/m 2 onwards and, under no circumstances must it go over cd/m 2. In order to control glare, it is convinient to divide sources into two large groups, that is to say, those which have a luminance under cd/m 2 and those with a luminance above this value. Sources under cd/m 2 include all normal types of fluorescent lamps. Luminaires belonging to this group of sources use, translucent materials and shielding for glare control. In some circumstances, lamp luminance is low enough to allow bare use. The group of sources above cd/m 2 includes for the most part compact lamp types, with an incandescent filament and varieties of gas discharge. Although both methods of glare control mentioned before are used in low power lamps, the shielding method is almost excusively used to control glare in the most powerful types, as far as industrial lighting goes. In these cases, illuminance in the observer s eye, such as luminance, must be taken into account. Because of this reason, both flux coming out and mounting height must be carefully considered when calculating shielding angles convenient for sources of this class. 148 LIGHTING ENGINEERING 2002

138 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Luminance range Quality class of glare Lamp type lamp average (cd/m 2 ) limitation A B C D E Lower than º 10º * Tubular fluorescent. From to º 20º High pressure discharge diffusers or fluorescent tubes. More than º 30º High pressure discharge Light glass tubular tubes. Light glass incandescent. Chart 2. Minimum shielding angles required additionally. Glare degree or quality class Curves comprise a scale of five degrees of glare corresponding to five quality classes (Chart 1). Degrees of glare emerge from glare subjective evaluation performed in a laboratory by a group of observers, using a nine point scale where the main points were marked. Standard servicie illuminance Standard service illuminance value, 300 lux onwards, is used together with quality class, as a parameter to select the limit curve of the adequate luminance. Ratio a/h Instead of the adequate range of critical ranges, a range of critical ratios a/h may be used, where a represents the horizontal distance and h the vertical distance between the observer s eye and the furthest luminaire (Fig. 6). These values are represented on the right side of glare diagrams. a γ Critical vision zone 45 hs Critical radiant zone tan γ = a hs 1.20 m. Figure 6. Critical radiant and vision zones. Luminance values Luminance distribution of luminaires in the C 0 -C 180 and C 90 -C 270 planes are initial values. Average luminance of the luminaire in a given direction may be calculated as the quotient between luminous intensity in such a direction and apparent luminous area. * For linear lamps seen frontways: 0. LIGHTING ENGINEERING

139 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Limitation curves are valid for: - General lighting. - Lines of vision predominantly horizontal or downwards. - Reflectances of 0.5, at least, for flat ceilings and walls, and, at least, 0.25 for furniture. For a luminous ceiling, glare limitation will be enough provided luminance in angles greater than 45º does not exceed 500 cd/m 2. Process for the use of the protection system from glare 1. Determine average luminance between 45º and 85º and the type of luminaire chosen for the installation. 2. Determine the quality class and the level of illuminance required for the installation (provided it is new). 3. Select the adequate curve (class and level) of the corresponding diagram. 4. Determine the maximum angle, for the length and height of the room, between the level of the eye and the luminaire plane. 5. Take the horizontal line of the glare limitation diagram for the value a/h found in the previous step. The part of curve over this line may be ignored. 6. Compare luminaire luminance with the chosen part of the limitation curve. There will not be psychological glare if the luminaire luminance value does not exceed the luminance specified by the chosen limitation curve within the range of the emission angles. If the result is different, the design must be modified, for example, selecting another type of luminaire. It is advisable to use this method only in indoor working areas. In other situations, that is to say, in public places, halls and entrances, higher illuminances may be required since sources of light in these places serve as an animation element. New development A new development in the area of glare systems is the C.I.E. Unified Glare Rating, UGR, which is a new evaluation system of psychological glare in indoor lighting. Although this system has not been internationally approved, it may be adopted to general use. UGR formula The formula to calculate the UGR value is the following: 0.25 UGR= 8 loge. L b L2. w p 2 R where: L b = background luminance (cd/m 2 ). L = luminance of luminous parts of each luminaire in the direction of the observer s eye (cd/m 2 ). =solid angle drawn by the luminous parts of each luminaire in the observer s eye (stereoradian). p = position index for each luminaire, which is related to the shift of the area of vision (Guth s position index for each luminaire) A more exact evaluation of glare is achieved by means of a direct application of the UGR formula for the considered installation, for which a computer program is required. UGR Charts A simpler UGR value may be obtained, although not as exact, using standard UGR glare charts. These charts provide the UGR value calculated for different standard situations and for different types of luminaires. A disadvantage of these charts is that luminaires cannot be classified. Due to this reason, UGR limitation curves have been developed. 150 LIGHTING ENGINEERING 2002

140 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING UGR limitation curves Glare limitation curves calculated using the UGR method are slightly different to limitation curves of the C.I.E. glare limitation described before. These comprehend five lines instead of eight, and the range of luminances covered is considerably larger. UGR C= C= º º 75º γ 70º 65º 60º 55º 50º 45º L (cd/m 2 ) Figure 7 The range of the glare index extends from 13 to 28 in groups of 3 units, this being the least increase provided by a significative change in the sensation of psychological glare. Another difference is that for these curves, luminaire classification is independent from illuminance. Thanks to curves luminaires may be classified. However, they are not as exact as charts, since only the luminaire effect is considered and not the effect of all the installation. Glare produced by windows Sky luminance in which glare begins to be perceived is approximately cd/m 2 and corresponds to horizontal illuminance of lux under cloudy conditions. Since sky luminance may not be diminished, glare produced by windows may only be prevented using curtains, blinds or lattices. Alternatively, working positions may be established in such a way that glare from windows does not interfere with the occupants field of vision. Psychological glare produced by windows may be reduced using very light decorations on surfaces close to window openings and spreading decorations on them, allowing incident light to reduce contrast from the window. Veiling reflections and reflected glare Brightness of a source of light reflected by a matte or semi-matte surface in the observer s eyes produces a slight or considerable discomfort. When this reflection is produced in a task is known as veiling reflection. When glare is produced outside the task, it is reflected glare. On top of producing discomfort, veiling reflections reduce the context of the task, and, as a consequence produce a loss of details. Both veiling reflections and reflected glare may be minimized in the following way: 1. Designing a lighting system or locating working areas in such a way that no part of the visual task is within or near the reflection angle of any bright source of light with respect to the eye. 2. Increasing the amount of light in both sides on the visual task, approximately in right angles to the direction of vision. 3. Using luminaires which possess a wide range of emission and low luminance. 4. Using working surfaces, paper, stationery, office machines, etc. with a matte surface to reduce effects from reflection. LIGHTING ENGINEERING

141 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Shadows and modelling The appearance of indoor areas is improved when their structural characteristics, objects and people are illuminated in such a way that silhouttes are seen in a clear and comfortable way, and shadows are formed with no confusion. Such a thing happens when light flows in an evident way in one direction more than in any other. The term modelling is used to describe the form in which silhouttes of three dimensional objects are stresssed by lighting. Modelling may be strong or weak; the most effective degree for any indoor area depends on type of construction and activities implied. When light comes from many directions and is too diffused, modelling may be light and the indoor area may be little interesting due to the loss of luminance contrast. Besides, if the directional component is very strong, modelling will normally be severe and shadows may be confused. However, pronounced shadows, like the ones obtained with sources of light concentrated in a small area, may be used to produce intentioned dramatic effects. Shops, art rooms and many other places will require lighting with a provision for modelled shadows in several degrees. A window or a big luminaire may produce good modelling without strong shadows, but if the source is very big in relation to the distance to the illuminated object, like in the case of indirect lighting, modelling will remain weakened. Profound shadows which produce excessive luminance contrasts may be softened by means of applying additional sources of light. Finishes with high diffusing reflectances in the surfaces of the room result in efficient secondary sources of light also reducing shadows, materially speaking, and reflecting a significant amount of diffused light within shadowy areas. Shadows with soft edges are obtained with sources of large areas such as fluorescent lamp luminaires or indirect lighting systems Light quality In chapter 4 devoted to The Colour, it was explained that the most important characteristics of the quality of light are Colour Temperature (T C ) and Colour Performance Index (R or R a ). Colour Temperature (T C ) has an important influence on the environment created as long as coldness or heat sensations go. At the same time, it promotes or reduces object chromaticity in the same way. Moreover, the term T C cannot be manipulated in an independient way, but it must be combined in an adequate way with illuminance so that disturbing effects of visual perception are not produced. Kruithof s curves delimit possible combinations between T C and illuminance calculation (Fig. 8). ILLUMINANCE IN LUX COLOR TEMPERATURE ºK Figure 8. Kruithof s curves for the ratio between T c and illuminance. 152 LIGHTING ENGINEERING 2002

142 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING The Chromatic Reproduction Index (R) is extremely important as far as quality of light goes, being the first measurement in activities where an optimal chromatic reproduction is absolutely essential (see chapter 4). Light and colour in indoor areas Apart from lamp colour properties, another aspect of colour which influences visual comfort in a room, is the colour diagram chosen for surfaces in a room. In general terms, light colours must be chosen to achieve high luminous efficiency for main surface areas. A white surface will reflect around 80% of the incident light, a light colour about 50%, a medium colour between 30% and 50%, and a dark colour less than 10%. In order to achieve the best results, materials and colours must be selected under equal or similar light to the planned one for the designed medium, apart from other factors of a subjective kind, climat, sex, age, colour surfaces which influence the rest of the colours, etc. LIGHTING ENGINEERING

143 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Lighting design Lighting is an art and a science. Therefore, there cannot be rigid or light rules regulating the design process. The basic purpose for a good lighting design is to create a lighting installation which will provide a good visibility for the task and, at the same time, a satisfactory visual environment. The function of a space enormely influences the way in which lighting must be applied. Therefore, spatial visual requisites have to be determined in the first place. Later on, and taken the results of these analysis as a basis, appropriate decisions for selection of lighting systems, lamps and luminaires will be made. In some cases, the lighting designer may choose the lighting system type; In other cases, architectural design and structural conditions may dictate a particular type installation. Indoor decoration and specially reflectances of the large surface rooms have a considerable influence in the lighting appearance. However, the most important fact is to have the design process in mind, consisting in two well- differenciated stages. The first stage begins with the client, and includes the study of different local factors which will influence the design. The second stage is the design process itself, and, it is in this stage where the first decision out of many more regarding design is taken Luminance distribution on surfaces Luminance distribution within a field of vision is an extremely important criterion in lighting design. It must be considered as complementary of indoor illuminance distribution. For a given lighting level, differences in luminance may be due to differences in surface reflectance. Although illuminance may be appropriate for the visual task, it will not necessarily provide an acceptable luminance balance in the indoor area. Such a balance will depend on chosen reflectances for surfaces. Lighting in this regard may contribute to improve the poorest situation, but the result will always be visually unsatisfactory. Therefore, luminance distribution must be considered as supplementary in indoor lighting projects. The following aspects must be carefully considered: 1. Luminance of the task and luminance of its surroundings. 2. Extreme values of wall and ceiling luminance. 3. Glare suppression, limiting luminaire and window luminances. In Fig. 9, the scale of luminances for indoor lighting may be observed. This is a very important fact for luminance distribution. cd/m Permitted luminance for general lighting luminaires Satisfactorily perceptible Barely perceptible Task preferred luminance Flat ceiling and wall preferred luminance Permitted luminance for luminaires in VDU working places Human face features (Recommended luminance for paths) Figure 9. Luminance scales for indoor lighting. 154 LIGHTING ENGINEERING 2002

144 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Luminance distribution for working areas If possible, luminances for the immediate surroundings of the task should be lower than luminances for the task, but, preferably, not lower than 1/3 of this value. This implies that the ratio for the immediate background reflectance of a task to the task itself should be in the range. This constitutes a practical or useful requisite for offices, but its application is difficult, and sometimes, even impossible. In most factories, the task is usually dark and the lighting designer may rarely specify the background reflectance Light emission depreciation Illuminance provided initially by a lighting installation will decrease in a gradual way during its use due to a reduction in lamp lumens, to lamps which burn down, and to accumulation of dirtiness in lamps, luminaires and surfaces of the room. However, it is possible to maintain illuminance at or above the minimum permitted value (known as maintained value) cleaning the lighting equipment and the room surfaces as well as replacing burned down or used up lamps at adequate intervals, according to a previously agreed maintenance program. The value for such maintenance program is indicated in Fig.10. Clearly for the case illustrated, illuminance in the non- maintained system will decrease up to a 40% of the initial value within the first three years and it will continue to decrease. But with a yearly cleaning, relamping and paint changing every three years, illuminance reaches 60% of the initial value. In three years, the maintained system provides an illuminance 50% greater than that of the system without maintenance Number of years, supposing hours working per year Loss due to lamp deterioration 80 Lighting percentage Loss for lamp dirtiness 71 Benefit for cleaning every six months Luminaires cleaned every 12 months Benefit for cleaning every six months Luminaires cleaned every 12 months Relamping also benefitial Cleaning twice a year and relamping Cleaning once a year and relamping Cleaning twice a year and initial lamps Cleaning once a year and initial lamps Working hours Figure 10. Depreciation combined curves showing the cleaning and renovation effect for an installation of fluorescent lamps. Factors to be considered in indoor lighting depreciation Dirtiness in lamps and luminaires For the most part, light loss may be attributed to dirtiness accumulated in lamps and light control surfaces (reflected, refracted or diffused) of luminaires. Depreciation speed caused by dirtiness which accumulates on light control surfaces is affected by the tilt angle, finish, and surface temperature, by the luminaire ventilation degree or tightness, as well as by the atmospheric pollution degree surrounding the luminaire. Depreciation in the emission of light may be reduced selecting appropriate luminaires for each place. Those luminaires with open bases and closed surfaces accumulate dirtiness more quickly than those with ventilation. In ventilated luminaires, convection currents take dust and dirtiness out through holes or slits in the canopy or reflector, and out of reflection surfaces. In highly polluted environments, it is better to use sealed or dustproof luminaires. Some of them possess a filter inside which LIGHTING ENGINEERING

145 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING allows the necessary breathing to take place. Dirtiness on the surfaces of the room Dirtiness accummulated on ceilings (flat ceilings) and walls reduces their reflectance value and, thus, the amount of reflected light. The connection between this and the calculation of illuminance will obviously depend on the size of the room under study and on the luminaire light distribution. The effect will be more pronounced in small rooms or when there is luminaires with an indirect component. Depreciation of the lamp flux Luminous performance of all lamps diminishes with use, but the speed of such diminution varies greatly according to types of lamps and manufacturers. Hence, calculations for lighting must bear in mind specified depreciation of the luminous performance of each lamp in particular. It must be taken into account that data shown in figures are based on certain suppositions related to working conditions. One or more of the following factors may influence the depreciation index: - Room temperature. - Lamp working position. - Supplied voltage. - Type of control equipment used, if relevant. Lamp failure Average life of a lamp depends on the type of lamp used and, for discharge lamps, on the ignition cycle. Failures in lamps cause not only a reduction in illuminance levels, but also an inacceptable reduction in the lighting uniformity degree. Maintenance factor (f m ) f m is defined as the ratio between illuminance produced by the lighting installation at a specified time, at the illuminance produced by the installation itself when it is new. f m, thus, combines losses caused by lamp depreciation flux, luminaire depreciation and depreciation of the room surface. If each of these depreciation causes is quantified by a specific period of use, a general factor product of the three factors is obtained. f m = lamp flux loss factor x luminaire loss factor x room surface loss factor When the light loss factor for different maintenance situations is calculated, it is possible to predict the illuminance situation produced by the installation in relation to the time elapsed Indoor lighting calculations Lighting levels and recommendations Before beginning lighting calculations, required values will be obtained for the type of activity to be developed in the premises to be illuminated. Such values may be found at the end of the chapter and they are: - Average illuminance in service. - Glare limitation quality. Beside these requirements, values for the dimensions of the premises are fundamental, the working plane height, as well as the luminaire mounting contour height Index of premises Premises to be illuminated are classified according to the relation that exists between their dimensions, mounting height and type of lighting. This is called index of the premises and it serves the purpose of determining the utilization factor. The utilization factor is calculated in the following way: - For direct, semidirect, direct-indirect and general diffused luminaires: 156 LIGHTING ENGINEERING 2002

146 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING A. L Ratio of premises = h. (A + L) - For indirect and semi-indirect luminaires: 3. A. L Ratio of premises = 2. h. (A + L) In both formulas: A = Width of the premises (m.). L = Length of the premises (m.). h= Mounting height (m.). The distance between the luminaire down to the useful or working plane is considered. The height of the premises, H, is the sum of the luminaire suspension contour height, C, plus the mounting height, h, plus 0.85* m. to which the working plane is from the ground. Since H and C are data previous to the installation, mounting height is calculated with the following formula: h = H C 0.85 (m.) Light loss or maintenance factor (f m ) In general terms, maintenance factors shown in Chart 3 may be established, which are the result of the working environment. This factor is obtained by multiplication of three factors (lamp flux depreciation, luminaire depreciation and depreciation of room surface), as it had been commented previously. Working environment Steel fabrication, melting areas 0.65 Welding industries, mechanized 0.70 Industrial offices, rooms 0.75 Operation patios, public premises 0.80 Offices, comercial and computing offices 0.85 Chart 3 F m Utilization factor or coefficient of utilization (f u ) Utilization factor of a lighting system is the ratio between luminous flux which reaches the working plane and the total flux emitted by the lamps installed. This is a very important fact for the calculation of lighting and depends on a diversity of factors, like: adequate value of lighting level, lighting system, luminaires, dimensions of premises, reflection (ceilings, walls and floor) and maintenance factor. In general, the reflectances method is used for its determination. Currently, there are also many situations and tabulated values according to each manufacturer and even computer programs for their users. When this factor is to be used, whether it is multiplied or not by the luminaire performance ( ) must be taken into account. This will later be used in the lighting calculation formula. *Distance at which the working plane is from the ground according to the Construction Technological Norm. LIGHTING ENGINEERING

147 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Calculation process Currently, this process is computerised (INDALWIN program). But in this section, the process to be followed to perform an indoor lighting project is going to be indicated. This will be done bearing in mind recommendations established by the C.I.E. as far as illuminances in service are concerned, direct glare quality limitation and colour rendering group (R or Ra) more highly recommended for a concrete installation (warehouses, offices, classrooms, etc.). The following steps must be followed: 1) Premises geometrical characteristics. 2) Reflection characteristics of different surfaces. 3) Obtaining required values for the type of activity to be developed in the premises (average illuminance in service, glare limitation quality, R), of the C.I.E. charts. 4) Selection of the type of luminaire to be installed according to the characteristics of the premises, which will define whether the luminaire is to be embedded, suspended or wall mounted. 5) Check that luminaires comply with the direct glare limitation quality. 6) Since an average level will be maintained in the installation, it is necessary to apply depreciation coefficients to initial values. These have been previously seen. 7) When lighting calculation for premises is done using the utilization factor method, it is necessary to know luminaire performance and utilization factor (for this reason, K value and ceiling, wall and floor reflections must be known). 8) Once all the data are known, the lighting fundamental formula is applied: where: E ms =. N.. f u. fm S E ms = Average lighting in service. = Lamp unitary luminous flux. N = Number of lamps (to be determined). = Luminaire performance. f u = Utilization factor. f m = Maintenance factor. S = Surface to be illuminated Some recommended lighting levels Construction areas in general Kind of area Illuminance in service Quality class Circulation areas, corridors 100 D-E Bathrooms, restrooms 100 C-D Businesses, warehouses 100 D-E Stairs, Escalators 150 C-D 158 LIGHTING ENGINEERING 2002

148 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Assembly workshops Kind of area Illuminance in service (lux) Quality classd Rough work: heavy machinery C-D assembly Medium work: vehicle body and B-C engine assembly Fine work: office machinery and A-B electronics assembly Very fine work: instrument A-B assembly Plastic, rubber and chemical industries Kind of area Illuminace in service (lux) Quality class Automatic processes C-D Interior plant general area C-D Control rooms, laboratories C-D Pharmaceutical manufacturing C-D Pneumatic manufacturing C-D Inspection A-B Colour combination A-B Clothing Kind of area Illuminace in service (lux) Quality class Ironing A-B Sewing A-B Inspection A-B Electricity industry Kind of area Illuminace in service (lux) Quality class Cable manufacturing B-C Coil winding A-B Assembly of telephones, radios A-B Evaluation, adjustment A-B Assembly of high precission parts A-B electronic components Food manufacture Kind of area Illuminance in service (lux) Quality class Automatic process 200 D-E General work areas 300 C-D Craft decoration 500 A-B LIGHTING ENGINEERING

149 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Smelting Kind of area Illuminance in service (lux) Quality class Smelting areas 200 D-E Preliminar workbench, preliminary nucleus construction 300 C-D Fine workbench, nucleus construction, inspection 500 A-B Ceramics and glass Kind of area Illuminace in service (lux) Quality class Furnaces/furnace rooms D-E Mixing rooms, rooms for C-D formation, moulding and furnising Finishing, enamelling and polishing B-C Polishing machine engraving B-C Polishing and manual engraving A-C Fine work A-B Metal manufacture Kind of area Illuminance in service (lux) Quality class Totally automatic 50 D-E production plants Semi-automatic 200 D-E production plants Work stations with permanent 300 D-E staff in production plants Control and inspection platforms 500 A-B Leather works Kind of area Illuminance in service (lux) Quality class General work area B-C Pressing, cutting, sewing, A-B shoe manufacture Classification, piling, quality A-B control 160 LIGHTING ENGINEERING 2002

150 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Machine and tool shops Kind of area Illuminance in service (lux) Quality class Small part cast D-E Preliminar workbench and machine C-D work, welding Intermediate workbench and B-C machine work Fine workbench and machine work, A-B inspection and verification Fine work, complicated and small A-B part measurement and inspection Painting works and spraying cabins Kind of area Illuminance in service (lux) Quality class Washing, rough spraying C-D Ordinary spraying and painting B-C Fine painting, spraying and A-B finishing, retouching and mixing Paper factory Kind of area Illuminance in service (lux) Quality class Automatic processses 200 D-E Board and paper manufacture 300 C-D Inspection, classification 500 A-B Printing works Kind of area Illuminance in service (lux) Quality class Printing machine C-D Binding A-B Composing, correcting, A-B cutting, and enhancing rooms Retouching, etching A-B Colour reproduction and printing A-B Copper and steel etching A-B Textile industries Kind of area Illuminance in service (lux) Quality class Carding, patterned cloths D-E Spinning, winding, dying C-D Twisting, weaving A-B Sewing, inspection A-B LIGHTING ENGINEERING

151 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Woodwork shops Kind of area Illuminance in service (lux) Quality class Sawmills D-E Assembly bench work C-D Wood machining B-C Finishing A-B Final inspection, quality control A-B Offices Kind of area Illuminance in service (lux) Quality class Archives C-D Conference rooms A-B General offices, typing, A-B rooms where computer- related activities are performed Open and deep offices A-B Drawing offices A-B Schools Kind of area Illuminance in service (lux) Quality class Workshops, libraries, reading rooms 300 A-B Classrooms, assembly halls, 500 A-B laboratories, art rooms, sports halls Shopping precincts Kind of area Illuminance in sevice (lux) Quality class Conventional shops 300 B-C Self- service 500 B-C Supermarkets, department stores 750 B-C 162 LIGHTING ENGINEERING 2002

152 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Public edifices Kind of area Illuminance in service (lux) Quality class Cinema auditorium 50 B-C Cinema foyer 150 B-C Theater and concert hall auditoria 100 B-C Theater and concert hall foyers 200 B-C Light- sensitive exhibits in museums 150 B-C and art galleries Exhibits insensitive to light in museums 300 B-C and art galleries Church naves 100 B-C Chancel, sanctuary and platform 300 B-C Houses Kind of area Illuminance in service (lux) Quality class Bedrooms in general 50 B-C Head of bedroom 200 B-C Bathroom in general 100 B-C Place to shave and make up in 500 B-C the bathroom House in general 100 B-C Place to sew and read 500 B-C Stairs 100 B-C Kitchen in general 300 B-C Kitchen s work area 500 B-C Desk 300 B-C Children s room 100 B-C Hotels and restaurants Kind of area Illuminance in service (lux) Quality class Dining rooms 200 B-C Bedrooms and bathrooms in 100 B-C general Bedrooms and private bathrooms 300 B-C Entrance lobbies and conference 300 B-C halls in general Kitchens 500 B-C LIGHTING ENGINEERING

153 Chapter 10. INDOOR AND INDUSTRIAL LIGHTING Hospitals Kind of area Illuminance in service (lux) Quality class Ward corridors at night A-B Ward corridors during the A-B night/afternoon Wards general lighting A-B Lighting in examination rooms A-B General lighting in local A-B examination rooms Intensive care and observation A-B Nurses stations A-B Pre- operation rooms A-B General lighting in A-B operating rooms Local lighting in operating A-B rooms General lighting in post- mortem A-B rooms Local lighting in post- mortem A-B rooms General lighting of laboratories A-B and pharmacies Local lighting of laboratories A-B and pharmacies General lighting in A-B consulting rooms Local lighting in A-B consulting rooms 164 LIGHTING ENGINEERING 2002

154 Chapter 11. FLOODLIGHTING 11.1 General remarks Utilitarian lighting Amenity lighting Sports lighting LIGHTING ENGINEERING

155 166 LIGHTING ENGINEERING 2002

156 Chapter11. FLOODLIGHTING General remarks The Committee for International Lighting (C.I.E.) defines floodlighting as: lighting of a place (scene, area) or of an object by means of floodlights in order to increase lighting strongly in relation to their surroundings. There is a great number of totally different application fields and lighting systems to which the term floodlighting is frequently applied (also the term directed lighting is used). The common technique to all floodlighting installations consists in the use of floodlights to obtain an increase in surface illuminance with regards to its surroundings. This important branch of lighting technique is probably the most widely linked to the development of countries and is having a generalized and important increase. The scale of applications open to floodlighting with amenity and utilitarian purposes is wide and varied. However, the most important ones are listed below: - Utilitarian lighting (large working areas). - Amenity lighting (buildings, monuments, bridges, parks and gardens). - Sports lighting. For each case, floodlighting is a problem to be solved individually. Sometimes, very narrow beams will be necessary, with a great intensity in candelas to reach areas or objects located at great distances. Some other times, certain opening angles will be required to achieve good uniformity in the lighting of the zone or field, adjusting the floodlight to its geometrical limits as much as possible. If the enormous variety presented by the three most important variables intervening in all cases is added (type of area, geometrical situation of lighting equipments and conditions of the environment or surroundings), it may be easily deduced that it is virtually impossible to establish a norm. Only for most cases of sports lighting (measure unification, rules of the game, etc.) it is possible to establish general norms, even though there are several variables. Therefore, to help the specialist who is going to design the lighting installation project, only the most important basic rules, recommendations, charts or data to bear in mind may be provided, always taking into account the specialist s criterion in order to supply deficiencies. Data collection It is the fundamental base to make ulterior decisions. The more data, the better, as far as planes, observations, possibility of locations, lighting hours, dirtiness acummulation prediction, surroundings of the area, streets, crossings, roads or nearby roads, power supply systems, estimate possibilities, etc. is concerned. - Lighting hours, needs in peak hours, glares, favourable contrasts, atmospheric conditions, etc. must be carefully considered in security, protection or production lighting. - Possible colour effects, shadows and contrasts, floodlight angles, surface reflectance, brightness of the surroundings, etc., must not be forgotten in decorative or architectonic lighting. - Possible vertical lighting exigencies, avoidance of shadows and glares to users or the audience, contrasts and game features or class (competition, club, training, leisure, etc.) will be preferably considered in sports lighting. Illuminance determination In case it is not provided, the recommendable level must be fixed bearing in mind all particularities and with the help of the charts present throughout this chapter and at the end of it. But not only the minimum luminous level for a correct perception of the object must be taken into account (always eased by the extraordinary eye adaptation capacity), but also the slightest visual fatigue of people subjected to the action of artificial lighting for long periods of time must also be avoided. Thus, accidents or a decrease of faculties may be avoided. LIGHTING ENGINEERING

157 Chapter 11. FLOODLIGHTING Utilitarian lighting This lighting system is integrated by those cases in which floodlighting is necessary because of security, protection or production purposes, constituting the only logic system to perform lighting. Many large areas, for example road intersections, ports, classification areas in railways, construction areas, storage areas, container complexes, etc., are illuminated using floodlighting with high columns. Lighting with high columns is preferred, mainly due to the fewer number of lighting columns used. This factor contributes to mobility in the illuminated area. Generally speaking, the high column system supposes a saving in expenses if compared to a system which uses lower columns. The saving is mainly in the total cost of columns, lamps, luminaires and cables, although there is also a reduction in maintenance expenses. General remarks Column height In order to calculate the column (tower or post) height in which floodlights will be mounted, avoiding a direct glare, the abacus in Fig. 2 will be used. It is important the fact that with excessive heights, the price of columns increases considerably. However, if heights are lower, the number of columns, lamps and luminaires increases very much. Also, if there are relatively high constructions in different positions within the area, mounting heights lower than those shown in the abacus must be used in order to avoid strong shadows projected on the area. When the emphasis lies in saving space and in the flexibility of use of the area, the columns used must be higher than those of the abacus, since an increase in height also increases the allowed space, and, the number of obstructions in the form of columns decreases, too. D Mounting height will be at least H=D/4 Figure 1 DISTANCE FROM THE COLUMNS TO THE EDGE OF THE AREA TO BE ILLUMINATED 0 m. 6 m. 12 m. 18 m. 24 m. 30 m. 36 m. 42 m. 48 m. 54 m. 60 m. 0 m. MOUNTING HEIGHT 6 m. 9 m. 12 m. 15 m. 18 m. 21 m. 24 m. 27 m. 30 m. 33 m. 36 m. 39 m. 42 m. 20 m. 40 m. 60 m. 80 m. 100 m. 120 m. 140 m. TOTAL WIDTH OF THE SURFACE TO BE ILLUMINATED 45 m. 48 m. 51 m. 54 m. 57 m. 60 m. MOUNTING HEIGHT Figure LIGHTING ENGINEERING 2002

158 Chapter11. FLOODLIGHTING Lighting levels At least the level required in the horizontal plane (horizontal illuminance) must be defined. Sometimes also vertical illuminance must be controlled (for example, where reading tasks take place, goods are inspected or moved). The necessary lighting levels and uniformities depend on the difficulty of the visual task, on the one hand, and on the degree of efficiency and security required, on the other hand. In Chart 1 level and uniformity requirements for different categories of areas are indicated. Visual task and Example Horizontal illuminance Uniformity factor category recommended maintained average (lux) Security Low risk areas Industrial storage areas; 5 1:7 occasional transit only Medium risk areas Vehicle storage areas, 20 1:4 containerterminals with frequent transit High risk areas Critical areas in petrochemical 50 1:2.5 works, chemical electricity and gas plants Movement and transit Pedestrians Only people movement 5 1:7 Slow moving vehicles Load/ unload trucks and/ or 10 1:4 bicycles Normal transit Public lighting in container 20 1:2.5 terminals, manouver areas General work Very rough Excavation, clearance 20 1:4 Rough Woodwork 50 1:4 Regular Masonery, woodwork 100 1:2.5 Fine Painting, electric works 200 1:2 Chart 1. Recommended illuminances and uniformities for outdoor working areas. Glare The degree of glare limit required depends, of course, on the category of the area under study (C.I.E.: Glare evaluation system for and outdoor sports area lighting). In general, discomforting glare will be reduced with an increase in the mounting height. Choosing floodlights well and having special care when pointing them may also help to maintain glare to the minimum. Sometimes, when glare is critical, special lattices must be placed on luminaires. Lamps High intensity discharge lamps are recommended as appropriate for area floodlighting. The most frequently used lamps are high pressure sodium discharge lamps, and metal halide ones. Even though when colour discrimination is not necessary and lighting levels are not excessively high, low pressure sodium discharge lamp offers a good solution. LIGHTING ENGINEERING

159 Chapter 11. FLOODLIGHTING Amenity lighting This lighting system is used when an advertisement, a facade, a building, artistic fountain or monument, etc. is to be illuminated due to purely decorative reasons, with the idea of attracting people's attention, embellishing an area or expressing civic proud, sometimes even used as an advertising way. In these instances, lighting belongs to the architectural vocabulary, being an art in which brightness, lights, shadows, colours and contrasts are manipulated Design general considerations During day- time hours, a building is illuminated by direct sunlight, diffused light radiated from the sky or both. The result is that the architectural characteristics of the building are highlighted by a varied show of lights and shadows. The design of a good lighting installation through floodlighting requires a careful study of the most attractive characteristics of the building and the effects of light on them. Therefore, the techniques to illuminate a building through floodlighting are not based on lighting engineering, because feelings and understanding of aesthetical values are equally important. Observation direction Normally, there are several directions from which a building may be observed, but, in general, one direction in particular may be considered as the main observation direction. Observation distance Observation distance is important since it determines the number of visible details on the structure to be illuminated. Surroundings and background If the surroundings and the background of a structure are dark, a relatively small quantity of light is necessary for the structure to be highlighted against the background. If there are other buildings illuminated through floodlighting in the surroundings, or buildings with illuminated windows, or a background with brightness, this will give a strong impression of luminance. Then, more light for floodlighting to produce the desired impact will be necessary. Another solution may be to create colour contrasts, instead of luminance differences. Obstacles Trees and railings surrounding a building may form a decorative element of the installation. An attractive way of doing so is by placing the sources of light in front of them. This has two advantages: first, the sources of light are invisible for the observer and, second, trees and railings are seen as silhouettes against the illuminated background of the facade, increasing the feeling of depth. Position and direction of floodlights Once the main line of observation has been chosen, the installation and focusing of floodlights will depend on the shape of the building or, better, on its ground plan or horizontal cross- section. Experience indicates that the best placing of floodlights in a building with a rectangular ground plan is the one indicated in Fig. 3. The main observation line is indicated by the arrow A and the position of floodlights by the points marked as B. Placing floodlights in the two extremes of the diagonal, a good luminance contrast between the two neighbouring sides of the building is achieved, and also a good perspective. Oblique beams of floodlights highlight the texture of materials forming the facade. As observed in Fig. 3, this installation for rectangular buildings is also applicable to those of a square ground plan. 170 LIGHTING ENGINEERING 2002

160 Chapter11. FLOODLIGHTING A A B A B B A B Figure 3 Also projecting elements (like balconies), walls or balustrades may enrich the appearance of a facade and must be taken into account, if included in the lighting structure. In this case, floodlights must be placed at a certain distance from the facade, in order to avoid excessively strong shadows. If there is not enough space for this, small floodlights placed on the projection itself may be used as complementary lighting (Fig. 4). Recess or concave elements like galleries or balconies will remain in the shadow when placing floodlights at a short distance from the facade. In these situations, complementary lighting placed on the recess parts themselves may be used. Light of another colour may be appropriate for this purpose. Lighting through floodlighting placed at a greater distance produces less shadows and eliminates the need for additional lighting. d d Change in the height of the shadow produced by variation of distance "d" Supplementary local lighting to reduce shadow intensity Figura 4 Some of the many alternatives to place luminous sources are: on public lighting posts or on posts specifically placed for this purpose; on the roof of a neighbouring building; on supports fixed to the facade itself or on the ground, behind low walls, bushes or hedges. Recommended lighting levels In order to determine the necessary level of illuminance to provide a structure with the required visual impact, factors such as brightness of the surroundings and background, material used in the construction, etc. must be taken into account. Three LIGHTING ENGINEERING

161 Chapter 11. FLOODLIGHTING points are important: 1) The darker the material, the higher the illuminance necessary to provide an impression of satisfactory brightness on it. 2) For a normal installation in which light is directed upwards on a vertical surface, the amount of light reflected that reaches an observer, and, therefore, brightness of the surface illuminated, will decrease with the increase of surface uniformity. 3) The necessary illuminance will be influenced by the combination degree between the spectrum of the source of light used and the colour of the construction material to a certain extent. Favourable solutions are obtained when the colour of the light is close to that of the illuminated surface. In Chart 2 elaborated bearing in mind those three points, recommended illuminances for lighting through floodlighting are shown. RECOMMENDED LIGHTING LEVELS Illuminance in Lux Correction coefficients Facade material Poor Good Very good M S Clean Dirty Light-coloured stone white marble Medium-coloured stone Cement Light-coloured marble Dark-coloured stone Grey granite Dark marble Light yellow brick Light brown brick Dark brown brick Pink granite Red brick Dark brick Architectonic detail Aluminium coating: natural finish Saturated lacquer thermic finish (10%) red, brown, yellow Saturated lacquer thermic finish (10%) blue, green Medium lacquer thermic finish (30-40%) red, brown, yellow Medium lacquer thermic finish (30-40%) blue, green Pastel lacquer thermic finish (60-70%), red, brown, yellow Pastel lacquer thermic finish (60-70%), blue, green Chart 2 Recommended lighting levels are those necessary to create a luminance of 4, 6 or 12 cd/m2 on the facade when the surroundings are poorly illuminated, well illuminated or with a lot of brightness, respectively. Values are valid for lamps with 172 LIGHTING ENGINEERING 2002

162 Chapter11. FLOODLIGHTING a wolfram filament of K and clean surfaces of buildings. Correction coefficients shown are multiplying Lighting of buildings The convenience that a building is illuminated through floodlighting is determined by several factors, including the shape and surfaces of the building, its features (which may be difficult to define), its architectural merit, its historical or social meaning and its surroundings. The appearance of a surface illuminated through floodlighting depends, among other factors, on its texture. Rough surfaces reflect some light in all directions and, thus, when it is illuminated, it appears more or less bright independent from the angle from which it is being observed. Moreover, glasses and other very polished surfaces, reflect all the incident light on them as a mirror. Due to this reason, they appear as dark and lifeless when illuminated and seen from normal positions (Figs. 5, 6, 7 and 8). Figure 5. Specular reflection (bright, polished surfaces, etc.). LIGHTING ENGINEERING

163 Chapter 11. FLOODLIGHTING Figure 6. Composed reflection (irregular, rough surfaces, etc.). Figure 7. Mixed reflection (barnished, non- polished surfaces, etc.). 174 LIGHTING ENGINEERING 2002

164 Chapter11. FLOODLIGHTING Figure 8. Diffused reflection (matte surfaces, etc.). It is obvious that these differences in the reflection properties of the surface of the material makes necessary a different lighting for each facade to obtain the desired luminosity in each case. Even the amount of dirtiness on the facade is important; the reflection factor of a clean facade may be more than twice that of the same dirty facade. The surroundings have a powerful influence in the effect produced by the buildings illuminated through floodlighting. For example, if there is a lake, river, channel, etc. near the building, this will be highlighted when its reflections are projected in water. Cathedrals, churches, castles, public buildings, bridges and old monuments are examples of buildings which generally respond well to floodlighting; some industrial and commercial buildings may be illuminated through floodlighting as an advantage for themselves and for their surroundings. Design basic conditions Apart from the ideas exposed before in "design general conditions", the following comments are generally applied to lighting design through floodlighting. The relevant aspects of each comment varies with the type of building and lighting requisites. a) Lighting contrasts are generally more important than their homogeneity, and shadows are as important as light reflexes. b) Lighting through coloured floodlighting allows the highlighting of different planes and the production of coloured shadows. As a general rule, colour should be used moderately and discreetely. c) The aspect of a building illuminated through floodlighting and specially that modelled with shadows, differs quite a lot from its appearance during daylight, mainly because the direction and distribution of light are different. This also changes with the direction of observation, and especially with the change of angle between the direction of observation and the direction of the main light flux. d) As commented before, the visual impact of a building illuminated through floodlighting depends considerably on the brightness of the surroundings; the darker the background, the more dramatic the effect and the less the amount of light necessary to highlight the building. LIGHTING ENGINEERING

165 Chapter 11. FLOODLIGHTING e) The form of a building illuminated through floodlighting is best highlighted when its contours are visible, its solidity is emphasized, and the corners are emphasized too, by illuminating the neighbouring walls with a different luminance. The shape of a building with a non- peaked roof is evidently complete when both, roof and wall, are illuminated through floodlighting. f) The solidity of towers, domes and column heads is emphasized if illuminated through floodlighting from no more than three directions in azimuth. g) A good pronounced modelling is always desirable, but it does not make sense to highlight small details on flat facades when the building is seen from a certain distance. h) Height is more pronounced if building lighting is reduced progressively from its base upwards. If the lowest parts of a building are hidden from observation at a certain distance by the structures of the surroundings, maybe it will be convenient to reduce brightness in the opposed direction, for example, towards the ground. Lighting of contemporary design buildings New materials and building methods have played an important role in the development of a distinctive style of contemporary buildings. For example, external and internal walls of modern buildings with a steel structure are not load- bearing walls and, therefore, they may be made of light materials and be pre- manufactured before installation; structures of reinforced concrete, some with roofs of 40 meters or more in height, are another typical element of the contemporary landscape. On condition that the structure is adequate, lighting through floodlighting may be used to emphasize social and architectural meaning of many civilian, commercial and educative buildings recently built. Maybe, it will also be propaganda for the products of the company which owns or rents the building. For example, in Fig. 9 an office building may be seen. It has a pre- manufactured reinforced concrete facade which was built for a company which manufactures concrete; lighting through floodlighting strongly reveals the forms of the material. Figure LIGHTING ENGINEERING 2002

166 Chapter11. FLOODLIGHTING Monuments Monuments should be illuminated through floodlighting in a way that indicates their style, age and their historical meaning wherever possible. Floodlights for monument lighting are similar to those for historical buildings in general. The effects of erosion and, if ceilings and walls have been destroyed or partially destroyed, should be reported. Lighting should be designed to achieve an effect without and apparent cause (Fig. 10). Figure 10 Floodlights for lighting of castles in ruins and similar monuments should be designed to emphasize the compact character of their structures and reveal the shape of their towers and other prominent elements (Fig. 11). Figure 11 The historical importance of a monument may be indicated by coloured light. For example, blue light may be used to create a mysterious atmosphere, and red light to indicate the scene of a battle. The splendour and magnificence of a monument may be manifested to the maximum only by means of a close and continuous cooperation between the architect of the project, the lighting engineer and, wherever appropriate, the archeologist, whose main interest is the preservation of the monument. The lighting equipment should not be attached to the structure of the building unless a special permission has been granted. LIGHTING ENGINEERING

167 Chapter 11. FLOODLIGHTING Bridges and viaducts In general, bridges are attractive elements and, when conveniently illuminated, they contribute to improve night- time landscape (Fig.12). There are too many types of bridges. Discussing lighting of each and every one of them individually is impossible, but the following criteria are applicable from a general point of view: Figure 12 - The shape and main elements of the bridge must be visible from a considerable distance. Most of the times it is desirable for bridges on roads to include accesses in the lighting project so that it is seen as a part of the road and not as an isolated element of the complex. Amenity lighting luminaires for roadway lighting should be treated as part of the lighting design. - The convenience for a bridge to be illuminated through floodlighting depends on the surroundings, the main directions and the observation distances, the importance of the structure and architecture of the bridge, its importance in the night- time decoration, and the materials with which it has been built. - Stone and reinforced concrete bridges generally respond well to lighting through floodlighting, but it may be difficult to show the shape and details in iron and steel bridges this way, due to the low reflectance and the small area projected of the members of the structure. However, other methods may be used. For example, lighting with ornamental lights, lamps supported by cables and chain, have been used in some hanging bridges with satisfaction, but an effective maintenance may be difficult. - Lighting should not distract attention from traffic (motorized, highway or maritime traffic) which goes under or above the bridge. If coloured lighting is used, a special care must be taken to avoid confusion with traffic signals. - Illuminance necessary to show the effective shape of the bridge will mainly depend on the type of bridge, its surroundings (including district lighting) and reflectance of the building materials. When the lighting system and location of floodlights has been decided, its type, number and voltage may be estimated using the INDALWIN calculation program. After the lighting system has been installed, the effects must be valued from a critical point of view, and adjustments must be done in situ. - The sides of a stone bridge or similar crossing a valley, a clearing or a river may be usually illuminated through mounted asymmetric rectangular floodlights in one or both banks. If light is directed from one of the sides mainly, the arches, wring walls, counterforts and balustrades will be emphasized through coherent shadows which will be formed. However, this system is not likely to be applied if the bridge is very long. Preferably, floodlights should be mounted under the bridge platform to minimize glare for traffic and pedestrians going over or under the bridge (Fig. 13). Floodlights that,must be mounted over the bridge height due to practical reasons should be conveniently oriented so that glare is restricted as much as possible. This type of bridges may be illuminated also through luminaires mounted on the bridge or near it and hidden from the normal observation angles or by a continuous row of waterproof fluorescent luminaires mounted on the railing. 178 LIGHTING ENGINEERING 2002

168 Chapter11. FLOODLIGHTING The latter system may be applied for the lighting of pedestrian bridge by using luminaires which direct part of the light to the sidewalk and part to the sides of the bridge. Often, the appearance of an arched bridge is improved if the lower part of the arches is illuminated, preferably with a different colour of light to the one used on the sides of the bridge. A very dramatic effect is produced leaving the sides without lighting (in the dark). It is difficult to delineate cables and chains of hanging bridges except for festive lighting, but their support towers may be generally illuminated by floodlights with a great advantage, using circular symmetrical floodlights with a narrow beam, mounted in the bridge or next to it and aiming upwards. Lighting of the zone of the bridge for motorized traffic is normally done with public lighting luminaires. Asymmetric floodlight Asymmetric floodlight Figure Lighting of entertaining and leisure areas Night- time lighting of public parks and gardens is essential for security purposes, especially of children, and increases the time during which leisure elements may be used. Lighting shows the beauty of flowered gardens, trees, bushes and fountains or lakes. Another objective is that of lighting dark areas. Trees and bushes: During the day, a tree is generally seen as a silhouette against a bright sky. If the tree is illuminated during the night, the situation is the opposite: the tree clearly protrudes against the dark sky. This dramatic effect is highlighted if the sources of light are hidden. Tree lighting sideways from below Figure 14 Luminaires may illuminate the foliage from a certain distance or be located next to the trunk lighting its branches from the ground upwards (Fig. 14). The first technique is appropriated for trees with a dense foliage, whereas the other type of focusing is appropriate for light foliage trees. Beautiful effects may be achieved using different coloured lights (Fig. 15). LIGHTING ENGINEERING

169 Chapter 11. FLOODLIGHTING Figure 15 If a superior frontal or vertical lighting is not desired or it is not applicable, flowered trees or with naked branches may be projected against a white or light coloured wall, fence or railing. Another subtle effect more interesting than frontal lighting from a visual point of vie, may be obtained by illuminating trees and bushes from behind. But in most cases, floodlights should be placed between the public and the objects to be illuminated. Glare may be avoided placing screens on floodlights, even though most gardens have many places to hide them, such as bushes, tree trunks or stumps, rocks, fences, small walls, etc. Alternatively, floodlights may be embedded in the ground (in this case, drainage possibility must be born in mind). In general, it is neither economical nor practical to illuminate but a few trees in the park; and due to aesthetical reasons, uniform lighting of the totality of an area through floodlighting is satisfactory very few times. The trees chosen should be important and beautiful species and placed in positions where depth and subtlety are given to the scenery Sports lighting General remarks The goal of lighting indoor or outdoor sports facilities is to offer an adequate environment to practice and enjoy sport events both on the part of the spectators and the players. From a logical point of view, needs will vary according to installation types (recreation, entertainment or competition) and activity level (amateur, professional or television broadcasting) Basic requisites When designing sports facilities ligthing, requisites and comfort of the following users must be taken into account: sportmen or players, judges or referees, spectators and broadcasting and mass media. Players and referees Players (sportmen) and referees (judges) must be able to observe clearly everything that is hapenning on the playfield to so that the sport event takes place in the best possible circumstances. Spectators Spectators must be able to follow the player s activity and the sport action making the least effort. The surrounding environment must be comfortable, which means that not only must the playfield or court be seen, but also the immediate 180 LIGHTING ENGINEERING 2002

170 Chapter11. FLOODLIGHTING surroundings. Lighting must help the spectator to enter and exit the sport installation security. This security issue is also very important for players. T.V. broadcasting For T.V. broadcasting, lighting must provide conditions that will secure a good quality colour image (Publication C.I.E. nº 83), both for general images of the play and close- ups of spectators and players. Transmission continuity In order to comply with T.V. transmission continuity, requirements in case of failure of the normal lighting system, a secondary system is generally installed to provide an emergency T.V. lighting Lighting criteria The most important lighting criteria for sports lighting are the following ones. Horizontal illuminance The illuminated area where the sport activity is taking place is the main part of the visual field of sportmen and spectators. Therefore, horizontal plane illuminance at ground level serves the purpose of establishing visual adaptation. Due to this fact, and also to the playfield area being used as a visual background, it is very important that there is an adequate horizontal plane illuminancce to achieve the correct contrast against the background. Horizontal illuminance is also very relevant in circulation areas, like anti- panic ligthing, used in case there is a failure of the normal lighting system to secure spectators movement in and out of the sports field. Recommended average illuminances in Chart 4 are maintained values. That is to say, they are values that must be reached during an installation operation period. For the required initial values, maintained values must be multiplied by the inverse of the maintenance factor (f m ). Vertical Illuminance Enough contrast must exist for the player s body to be identified. This is only obtained if vertical planes are well illuminated, since this kind of illuminance is essential to recognize objects. Vertical illuminance is characterized by magnitude and direction. For players, a vertical illuminance is important from all positions. However, for spectators and cameras occupying a certain position, vertical illuminance must only be considered for such positions. For cameras with different positions, vertical illuminance on the four lateral planes of the field must be taken into account. In practice, vertical illuminance required for players and spectators is automatically obtained if horizontal illuminance requisites are observed. Therefore, from a practical point of view, vertical illuminance which must be measured at a 1.5 metre height over the playfield, is only a design criterion when considering T.V. transmission continuity, since it plays a major influence on image quality. Vertical illuminance must guarantee not only a player s recognition or image quality but also the fact that spectators and players are easily able to follow a ball, a ring, etc. that are flying over the playfield. Spectators and tribunes are part of the camera visual medium. Therefore, an adequate vertical illuminance must also be created for tribunes. Illuminance uniformity A good vertical and horizontal illuminance uniformity in horizontal and vertical planes is important. It avoids adaptation problems for players and spectators and it eliminates the need for continuous adjustment of cameras in different visual directions. If uniformity is not good enough, there is the possibility (especially with television cameras) that a ball or player will not clearly be seen in certain positions in the field. Uniformity may be expressed as the ratio between minimum illuminance and maximum illuminance (U 1 ) or as the ratio between minimum illuminance and average illuminance (U 2 ). In order for cameras to obtain the best possible visual conditions, the ratio between average illuminance on the horizontal LIGHTING ENGINEERING

171 Chapter 11. FLOODLIGHTING plane and average illuminance on the vertical one must be kept between 0.5 and 2 in general. Glare Glare occurs whenever a discomfort bright area approaches or enters the visual field, producing a disturbing effect for players and spectators. Glare may be minimised paying careful attention to floodlight or luminaire choice. We must also make sure that they are carefully focused, taking into account the main visual directions. Evaluation of glare The C.I.E. has developed a basis to evaluate the subjective impression of glare in outdoor areas. Essentially, it includes a glare index in which the lower the reaching is also, the lower the glare. Glare Rating (GR) is obtained this way: 0,9 L GR = logee. vl L ve R R where: L vl = veiling luminance produced by luminaires. L vl = Ε eyej Φ i 2 where E eye,i is the eye illuminance produced by the source of light (lux) i, and i is the angle between the direction of vision and the direction of incident light from the source of light i (degrees). L ve = veiling luminance produced by the medium. L ve may be approached from the horizontal average illuminance where the sports event is taking place, E hav, using the following formula: where p = the area reflectance. L ve = E hav. p For L vl the sources of light are luminaires, whereas for L ve the field and luminous surroundings are considered as an infinite number of small light sources. It is necessary to calculate GR for the observer s most critical positions, defined in Fig. 16. for a football playfield. 182 LIGHTING ENGINEERING 2002

172 Chapter11. FLOODLIGHTING 300 m. 300 m. 300 m m. 300 m. 1/4 A 1A /2 A /4 B 1/2 B 1B 1/4 A 1-11 Observer s position for GR calculations Reference positions to calculate veiling luminance outside the playfield area Figure 16 Nowadays, international sport associations are introducing their own GR norms and veiling luminance. External glare In past times, glare was only taken into account for players and spectators who were in the illuminated area or very close to it. Nevertheless, in case of outdoor lighting sports, the disperse light of the installation may bother spectators who are outside the playfield: for example, for traffic on adjacent roads or for those people who live in the surroudings. Currently, the C.I.E. is studying a direct parameter to quantify such disturbance, which is directly related to the optical quality of the floodlights used. This means that in order to avoid this inconvenience, floodlights must be chosen taking into account the limitation of the disperse light outside the main beam. They must be focused and mounted in an adequate manner. Recommendations Although glare ratio, or GR, is not specified in the recommendation sections, it is highly important for all sports lighting installations. It must coincide with the GR values established in the Publication C.I.E. n 83. The calculated GR value depends partially on the reflectance area where the sports activity is taking place. For grass courts, a diffused reflectance of about 0.15 to 0.25 is generally presupposed. The GR value must be determined for the observer s positions of such a sport, at a height of 1.5 metres over the area where the sports activity is taking place. The observer must see all points at ground level. For an outdoor installation, the effect of disperse light outside the precinct at a distance of 300 metres from the centre of the area must be calculated. This means that veiling luminance must be calculated at a 1.5 metre height over the ground for the five most extreme positions. Modelling and shadows Modulate is the lighting capability to reveal forms and textures. This is particularly important to provide a general vision of sportmen, LIGHTING ENGINEERING

173 Chapter 11. FLOODLIGHTING players, ball or other elements and spectators who are in the area where the sports activity is taking place or near it. The efficacy of modelling depends on directions from which light sources come from as well as on the number and type of sources used in it. Modelling may be hard, produced by means of deep shadows, for example, using floodlights with a narrow and simple beam; or soft, resulting from lighting without shadows from a luminous ceiling, for example. None of these extremes is advisable. However, for the latter case, it is possible to add some small floodlights to improve modulate. Good quality television images require a good modulate for lighting. This is the reason why up to 60% of the installed total flux may come from the side of the main camera, and 40% or even more, from the opposite side, in order to limit length and hardness of projected shadows for sportment where an asymmetric arrangement of floodlights is used. Colour appearance and reproduction A good colour perception is important in most sports, and, although some distortion due to artificial light is accepted, it must not be so much as to produce colour discrimination problems (between partially distorted colours). Two important aspects related to colour must be distinguished. - Light colour appearance: It is the colour impression in all the medium created by the lamp. - Light colour reproduction: It is the ability of light to reproduce colours of objects. Both colour appearance and colour reproduction of the light emitted by lamps depend on the distribution of spectral energy of theemitted light. One indication of the colour appearance of a lamp may be obtained from its colour correlative temperature, measured in Kelvin (K), which varies between and K. If colour temperature is lower, light colour impression will be warmer. The higher colour temperature, the colder or more bluish light colour impression. Colour reproduction properties of a luminous source may be indicated by the colour reproduction index (R). The maximum theoretical value of the colour reproduction index is 100, which may be compared with daylight. The visual characteristics of the surroundings depend on the R. The higher the R, the more comfortable the environment Design considerations Luminaire type Floodlights Floodlights are classified according to their light distribution: Circular floodlights (Fig. 17) There are two types of circular floodlights used in sports floodlighting: a) With a symmetric beam in a conical shape. They may have a narrow beam or a wide beam. b) With a slightly asymmetric beam on the vertical plane. They may have a narrow, medium, wide and very wide beam. Figure 17. Circular floodlights. Rectangular floodlights (Fig. 18). There are two types: a) With asymmetric distribution of light on horizontal and vertical planes. The beam is wide on the horizontal plane, whereas, it may be wide or narrow on the vertical plane. b) With symmetric distribution of light on the horizontal plane and asymmetric distribution of light on the vertical plane. The 184 LIGHTING ENGINEERING 2002

174 Chapter11. FLOODLIGHTING horizontal beam is wide. Figure 18. Rectangular floodlights. Circular floodlights require the use of a source of light more or less narrow, such as a short discharge tube of a high intensity discharge lamp. When it is not focused downwards from a vertical point of view, the conical beam emits an elliptical or almost elliptical light modelling over the field (Fig. 17). Rectangular floodlights are used together with their linear sources such as tubular discharge lamps and halogene ones. A fan- shaped beam produces a very trapezoidal model of light on the sports area where the activity is practiced (Fig. 18). Figure 19. Lateral disposition. When rectangular floodlights are mounted in a not very separate way on the sides of a sports area (normal disposition for a small area) two advantages are met if compared to the circular unit: light distribution is more uniform and light loss is less (Fig. 19). However, the circular floodlight is more efficient than the rectangular unit when used in the four corners, diagonal disposition (Fig. 20), whenever several units per column are used. Figure 20. Diagonal disposition. For all types of symmetric rectangular floodlights, a special shielding device or louver may be used, on condition that the floodlight is focused towards a direction producing glare. Such floodlights are designed in such a way that their maximum intensity is not in the centre of the beam, but towards one side. Luminous intensity diminution on each side of the axis beam is placed in such a way that when it focus a certain point on the surface, a more or less uniform horizontal illuminance is produced. In order to limit glare, intensities decrease rapidly from a certain light incident angle, making light distribution even more asymmetric. LIGHTING ENGINEERING

175 Chapter 11. FLOODLIGHTING When glare may produce important discomfort to people outside the area where the sports activity is practiced, luminous intensities outside the current beam must be the lowest possible. For this application, a floodlight that may distribute light totally under the horizontal plane is recommended Lighting design Lighting calculations In daily practice, it is very common to use computer programs (INDALWIN) to design sports lighting installations. The results of the program show quantitative values for most of the parameters, such as vertical and horizontal illuminances, uniformity and glare ratios. Floodlight orientation and location Calculations done with the computer assume that small groups of floodlights in a power supply network are located in a single point, that is to say, in the centre of the group. Such calculations are generally exact enough for general applications. However, when there are large groups of floodlights and the spacing between the external units is considerable, the calculation may result inexact in the focusing (Fig. 21). In these cases, a point of reference is determined for each small group of floodlights. γ γa γ A ε Error in the focusing of floodlight S when the same focusing angle is used for very spaced floodlights. Figure 21 Calculation matrix Since the distance between the matrix points is relatively small, the value shown for each point represents the area surrounding such a point (Fig. 22.). Matrix sizes commonly used are: - from 1 to 2 m.: For small playing areas. - from 5 m.: For football, hockey or rugby. In order to specify horizontal illuminances, the matrix must be at ground level, whereas in order to specify vertical illuminances, it generally is at 1.5 m. over such a level. 186 LIGHTING ENGINEERING 2002

176 Chapter11. FLOODLIGHTING 1/2 S x S x 1/2 S y S y S =Sx, Sy. matrix spacing =Point on which lighting is calculated. =Calculated value valid for this area (Sx, Sy) Figure 22 The positions of the observer and the observation or vision directions used when calculating glare are defined in the matrix. Camera positions Camera positions must be known to secure that lighting in such directions is adequate. These are specified as points of reference in the computer program, and generally speaking, separate calculations are done for a number of points Football fields Because of practical reasons, lighting requisites for different activities taking place in different periods of the year in outdoor football fields, must have floodlighting systems. Therefore, they may be defined in general. Illuminance When the events are regularly broadcasted from a stadium or football field, the floodlight lighting project is generally designed to provide the high illuminance necessary to comply with television requisites. The necessary horizontal illuminance for a play field depends on: a) The competition level taking place on it. b) The speed of the ball (also the rapid movement of players must be taken into account). c) The maximum distance between players and between any of them and the ball during the game. If the play field has tiers for spectators and the distance between the centre of the field and the most distant spectator is greater than the maximum distance existent between a player and the game object, the latter is the one that must be taken into account as a reference criterion. In Fig. 23, the minimum horizontal illuminance levels recommended for different distances between spectators and the centre of the field are represented. LIGHTING ENGINEERING

177 Chapter 11. FLOODLIGHTING Distance from the spectator to the centre of the playfield Horizontal illuminance Competition level Professional/ colour T.V. Competition Training Leisure Figure 23 Vertical illuminance is characterized not only by its magnitude but also by its direction. Vertical illuminance is considered on a vertical plane in a straight angle with the observer s line of vision (Fig. 24). Position of observer 1 Position of observer 2 Figure 24. Vertical illuminance planes for different observer s positions. An adequate vertical lighting from all directions is very important for players. Nevertheless, if it is checked in the four directions parallel to the play field exterior lines, it will be the adequate one in the rest of directions. For spectators and cameras occupying a fixed position, only vertical lighting seen from that place must be verified. In the charts at the end of the chapter, minimum vertical illuminance levels recommended for T.V. broadcasting are shown. 188 LIGHTING ENGINEERING 2002

178 Chapter11. FLOODLIGHTING Uniformity ratio Illuminance uniformity necessary on the field and surrounding courts depends on what is happening. For example, greater light uniformity is required for television broadcasting than for game development or following of a competition without broadcasting by the naked eye. A lower uniformity may be accepted for training than for competition. See Chart 3. Glare Glare should not be discomforting unless: a) Floodlights with a precise light control are used and correctly pointed. b) Floodlights are mounted far from the important observation directions. Mounting angles measured from the centre of the field should be higher than 20º on the horizontal. c) The least number of floodlight groups is used or a one- sided disposition. The number of groups in any of the field sides should not be greater than 4. d) Illuminance on the field of vision (which includes the field and the areas opposed to spectators) is as high and uniform as possible, consequent with the avoidance of too much illuminance in the spectators' eyes. In practice, this means that average illuminance on planes vertical to the height of the spectators eyes opposite it should not be greater than half their average value on the vertical over the field, and preferably not more than 1/3. If these requisites are met, the size and luminosity of individual sources and the number of floodlights in each group is not very important with respect to glare. They have a stronger effect on illuminance on the field. Experience has proved that glare of a correctly planned installation does not increase when illuminance is greater. Illuminance on vertical planes; modelling If floodlights are mounted at more than 30º on the horizontal measured from the centre of the field, the expense of towers is normally unaffordable. The reason for illuminance on vertical or almost vertical planes to that of horizontal ones is lower than expected, and modelling is not satisfactory. In general, the best balance between glare degree and illuminance on vertical planes is obtained when floodlights are well pointed and illuminance at the level of the spectators' eyes in front of it is within the given limits. The most adequate modelling is obtained with floodlights mounted in 4 towers at the corners (Fig. 28). The effect is lower with 6 towers, even less with groups of floodlights laterally mounted, and even less with continuous lines close to laterally mounted floodlights. Moreover, with lateral lighting, illuminance on vertical planes opposed to the band line is higher than with the systems of towers in corners. The advantages and disadvantages of the various floodlight lighting systems are discussed later in the chapter. Floodlight lighting systems To a great extent, the following descriptions of floodlight lighting systems reflect conditions which are necessary for football or similar games, but they will be generally satisfactory when other events take place in the stadium. Lateral lighting systems A lateral lighting system using 4 groups of floodlights on each side of the field is observed in the upper half of Fig. 25. The lower half shows the design for 3 groups of floodlights. LIGHTING ENGINEERING

179 Chapter 11. FLOODLIGHTING l/8 l/4 l/4 l/4 l/8 Design for four poles a l/6 Design for three poles l/3 l/3 l/6 l Figure 25 Small training fields may be illuminated from fewer positions and sometimes only from one side. Rectangular symmetric or asymmetric floodlights (which produce a fan- shaped beam) are used for most lateral lighting projects. The recommended mounting height is deduced from Fig. 26, the characteristic angles being measured from the longitudinal line of the centre of the field and the band line. 12 m. minimum 75 max. 45 min. Objective 25 Maximum 30 Minimum 20 Figure 26 When three groups of floodlights are used, these should be pointed to obtain an acceptable illuminance uniformity along the nearby band line. Choosing an appropriate number of floodlights for each tower, illuminances that may be provided go from adequate low values for training fields, up to high values necessary for colour T.V. broadcasting. Illuminance on vertical planes on the play area is approximately equal to that of the horizontal planes. Modelling is relatively insignificant and several shadows may be clearly seen. A careful pointing is necessary to avoid inadequate glare. Fig. 27 shows the design of lateral floodlight systems where floodlights are mounted in single rows under each side of the field and provide the necessary high illuminance for colour T.V. Mounting heights of floodlights are defined by the angles given in Fig. 26. The row of floodlights should be preferably extended beyond the goal lines in order to maintain a reasonable illuminance uniformity, especially in the areas, and provide light over the players so that they are seen behind the goal posts. 190 LIGHTING ENGINEERING 2002

180 Chapter11. FLOODLIGHTING However, this extension may not be possible in practice. Then, trimmer in illuminance towards the goal lines should be restricted by a reduction of the space of floodlights towards the end of lines or by the pointing of final floodlights outwards. As for other systems of lateral lighting, average illuminance on vertical planes on the play area is approximately equal to that of the horizontal ones and a careful pointing is necessary to avoid excessive glare. Where floodlights are mounted on ceilings (shelters) of tiers, the compensation distance may not be large enough to provide adequate vertical illuminance on the closest band line. Then, extra floodlights will be needed and should be mounted under the ceiling (shelter) at the necessary compensation distance. Figure 27 Systems of towers in corners The design used for 4 towers in corners is the one observed in Fig. 28. Recommended heights for the tower are deduced from Fig. 26. Normally, symmetric circular- shaped floodlights are used giving a symmetric beam. Individual beams may be joined to fill what is seen as a playing area in a non- rectangular form from the above structure. This allows an adequate illuminance design to be increased over the field. Angular compensations of 5 and 15 degrees, respectively, from the centre of the band line and the goal entrance provide adequate locations for the towers. In practice, location of the tower is ordered more often by the disposition of the place than by the ideal lighting requisites. Large stadiums, and specially those with courts outside the play field, are difficult to illuminate enough from the 4 corners. Very high towers would be necessary to comply with the angular requisites in Fig. 26, and glare from the long reach floodlights which would be necessary, would be probably excessive. Because of these reasons, the 6 tower system seen in Fig. 29 is preferred. The tower height is defined from the centre of the half of the field and approximately twice as many grouped floodlights in the central towers as those in the corners. Pointing angles are sharp and glare may be controlled quite easily. The illuminance ratio between vertical planes and horizontal planes is approximately 0.7. LIGHTING ENGINEERING

181 Chapter 11. FLOODLIGHTING 5 15 Figure Figure 29 Shadows of tiers The position of shadows projected in the field by tier ceilings and other obstacles may be obtained from the sketch seen in Fig. 30. If possible, height and location of the tower must be chosen so that shadows do not fall on the play field. Wherever this is not possible, additional floodlights should be mounted under the tier ceiling and directed towards the shadowed areas with the same average angle of the main floodlights. 192 LIGHTING ENGINEERING 2002

182 Chapter11. FLOODLIGHTING a= d H h-h h Tower D= d h h-h Tier H a D d Tower Tier Shadow area Figure 30 Atmospheric absorption losses Dust and humidity in the air make light to be lost by absorption and dispersion, depending on the amount lost of the stadium localization, projection length of floodlights and atmospheric conditions at the same time. The UEFA and CIE recommend that a discount of 30% of light lost should be done in calculations. Dispersion of light caused by fog, mist or rain produces veiling glare with the consequent reduction of visibility. Very little may be done about this, but there is evidence and it is that the effect is the least with the tower systems in corners that with the lateral lighting systems. LIGHTING ENGINEERING

183 Chapter 11. FLOODLIGHTING HORIZONTAL ILLUMINANCE LEVEL CHARTS Sport Activity level E (lux) U 1 U 2 R T c Group Archery (indoors) - shooting zone t/r ca cp n.a. - target t/r 300* n.a. n.a ca 500* n.a. n.a cp n.a. Archery (outdoors) - shooting zone t/r ca cp n.a. - target t/r 100* n.a. n.a ca 200* n.a. n.a cp n.a. Athletics - indoors t/r ca cp outdoors t/r ca cp Badminton t/r ca cp Baseball - in the field t/r ca cp outside the field t/r ca cp Basketball - indoors t/r ca cp outdoors t/r ca cp n.a. Cycle racing - indoors t/r ca cp outdoors t/r ca cp A B B B B 194 LIGHTING ENGINEERING 2002

184 Chapter11. FLOODLIGHTING HORIZONTAL ILLUMINANCE LEVEL CHARTS Sport Activity level E (lux) U 1 U 2 R T c Group Billiards all Sleigh t/r/ca cp Bowls -approximations, t/r greens and rinks ca cp pins t/r 300* n.a. n.a ca 300* n.a. n.a cp 500* n.a. n.a Boxing See martial arts Cricket - in the field t/r/ca cp outside the field t/r/ca cp Curling - tees/court t/r ca cp Darts t/r 300* n.a. n.a ca 500* n.a. n.a cp 1.000* n.a. n.a Greyhound racing t/r/ca cp Fencing t/r Ca cp Football - indoors t/r ca cp outdoors t/r ca cp Golf driving - tee/green t/r ca cp n.a. - fairway/range t/r 30* n.a. n.a ca 30* n.a. n.a cp n.a. A B C A A B C B LIGHTING ENGINEERING

185 Chapter 11. FLOODLIGHTING HORIZONTAL ILLUMINANCE LEVEL CHARTS Sport Activity level E (lux) U 1 U 2 R T c Group Gynastics t/r ca cp Handball - indoors t/r ca cp outdoors t/r ca cp Lawn hockey - indoors t/r ca cp outdoors t/r ca cp Ice hockey - indoors t/r ca cp outdoors t/r ca cp n.a. Equestrian sports - indoors t/r ca cp outdoors t/r ca cp Horce racing t/r/ca cp Judo t/r ca cp Karate See martial arts Lacrosse t/r ca cp Martial arts t/r ca cp B B B B A B B C C 196 LIGHTING ENGINEERING 2002

186 Chapter11. FLOODLIGHTING HORIZONTAL ILLUMINANCE LEVEL CHARTS Sport Activity level E (lux) U 1 U 2 R T c Group Car racing - indoors t/r ca cp outdoors t/r ca cp Tennis t/r ca cp Pelota court t/r ca cp Roller skating t/r ca cp Rugby t/r ca cp Shooting (indoors) - shooting zone t/r ca cp n.a. - target t/r 500* n.a. n.a ca 1.000* n.a. n.a cp n.a. Shooting (outdoors) - shooting zone t/r ca cp n.a. - target t/r 200* n.a. n.a ca 400* n.a. n.a cp n.a. Figure skating - indoors t/r ca cp outdoors t/r ca cp n.a. Speed skating - indoors t/r ca cp outdoors t/r ca cp B C C B B A A B B LIGHTING ENGINEERING

187 Chapter 11. FLOODLIGHTING HORIZONTAL ILLUMINANCE LEVEL CHART Sport Activity level E (lux) U 1 U 2 R T c Group Skiing t/r ca cp Skiing jump - sliding t/r ca cp winning post t/r ca cp Swimming - indoors t/r ca cp outdoors t/r ca cp Table tennis t/r ca cp Taekwondo See martial arts Tennis - indoor (PPA) t/r ca cp indoor (TPA) t/r ca cp outdoor (PPA) t/r ca cp outdoor (TPA) t/r ca cp Diving board t/r ca cp Volleyball - indoor t/r ca cp outdoor t/r ca cp B B A C B A B 198 LIGHTING ENGINEERING 2002

188 Chapter11. FLOODLIGHTING Legend for chart 3: t: Training (amateur and professional). r: General recreation. ca: National competition. cp: National and international competition without T.V. requisites. E: Minimum average horizontal illuminance at ground level or, when it is signalled with *, minimum vertical illuminance. n.a.: Non applicable. U 1 = Illuminance extreme uniformity (Emin/Emax) U 2 = Illuminance average uniformity (Emin/Emed) R: Colour reproduction index. T c = Colour temperature (in Kelvin s degrees). Group Maximum Illuminance Uniformity distance Main Secondary Vertical Horizontal R T c camera camera U 1 U 2 U 1 U 2 A B C 25 m 500 lux 500 lux m 700 lux 500 lux m lux 700 lux m 700 lux 500 lux m lux 700 lux m lux lux m lux 700 lux m lux lux m n.a. n.a. Chart 4. Recommended lighting for national T.V. Group Maximum Illuminance Uniformity distance Main Secondary Vertical Horizontal R T c camera camera U 1 U 2 U 1 U 2 A 25 m 700 lux 700 lux (1) (2) 75 m lux 700 lux (1) (2) B 150 m lux lux (1) (2) 25 m lux 700 lux (1) (2) 75 m lux lux (1) (2) C 150 m lux lux (1) (2) 25 m lux lux (1) (2) 75 m lux lux (1) (2) 150 m n.a. n.a. Chart 5. Recommended lighting for international T.V. (1) An R of 65 is admissible, but 90 is advised. (2) A Tc of K is admissible, but 5,500 K is advised. LIGHTING ENGINEERING

189 Chapter 11. FLOODLIGHTING 200 LIGHTING ENGINEERING 2002

190 Chapter 12. ROAD LIGHTING 12.1 Decision making criteria on road lighting Project situations, types of lighting systems and lighting levels Lighting engineering calculations Lighting systems LIGHTING ENGINEERING

191 202 LIGHTING ENGINEERING 2002

192 Chapter 12. ROAD LIGHTING Decision making criteria on road lighting Objectives The fundamental objective of road lighting is to allow a secure and comfortable vision during the night. Such qualities may protect, ease and improve motor traffic. An adequate use of public lighting as an operative instrument provides economic and social benefits like: a) Reduction in accidents at night- time, including human endangered lives and economic losses. b) Help to police protection and safety of population. c) Easier traffic. d) Promotion of transport and travelling at night. The aim of public lighting is to provide the driver with the necessary visibility to distinguish obstacles and road layout with enough time to maneuver in order to guarante security, apart from providing the automobilist with visual comfort while driving Night- time driving and users visual capacity The visual environment of an automobilist driving at night is basically formed by the roadway. Visibility of an obstacle located on the roadway, will depend on the luminance difference between the obstacle and the background, constituted by the roadway on which it may be seen. In the case of a light- coloured object on a dark background, its contrast is positive. However, an object darker than its background is seen as a silhouette and its contrast is negative. Road lighting generally produces negative contrasts for dark objects or obstacles or those with low reflectance. Night- time driving implies a mesopic or twilight vision comprised in the interval between 10-3 and 3 or 4 cd/m 2. It is characterized by a reduction in visual sharpness and a diminution in contrast differential sensitivity. A high luminance contrast threshold is necessary for obstacle visibility. Likewise, this kind of vision in night- time driving implies an important alteration in distance judging (deficient binocular vision), a limited perception of lateral obstacles and, finally, rare and unusual chromatic vision. It must be taken into account that vehicle headlights only illuminate a limited area ahead of them, while public lighting provides light to the road and its surroundings, opening the field of vision to the driver. This results in an approach to day- time light conditions, which may be important in certain traffic or environmental circumstances. On the other hand, differential sensitiveness to contrast for any same driver is more than three times higher in a road provided with lighting (2 cd/m 2 ), when compared with that provided by a vehicle traffic beam (0.2 to 0.3 cd/m 2 ). Visual sharpness during night- time driving evolves in such a way that for a driver on a road provided with lighting, visual sharpness becomes two and a half times higher than for the same driver using only the vehicle dipped headlights. For night driving with a vehicle dipped headlights ( cd/m 2 ), the efficacy of binocular vision is reduced to one third (1/3) of that reached during the day. Consequently, distance perception and judgment decreases considerably, implying a higher risk of accidents Decision making criteria for the need of road lighting A selection of possible road segments must be conducted in order to determine which should be provided with public lighting. There is a need, then, for establishing factors and criteria which will determine the introduction of such installations. Factors influencing lighting Some factors to take into account when implementing public lighting are the following: 1. Road type (motorways, dual carriageways, express roads or conventional roads), its location and its layout. 2. Conflict areas, such as crossroads, complicated crossings and special parts. 3. Traffic intensity and composition. Lighting installation criteria in road segments recommend to bear in mind factors influencing the need for lighting, as well as considering situations in which due to traffic intensity, only the car dipped headlights can be used for a long period of time. In conventional roads, changes from full lights to dipped lights in order to avoid glares must be done at an approximate LIGHTING ENGINEERING

193 Chapter 12. ROAD LIGHTING distance of 500 m. between vehicles circulating in opposite directions. Therefore, the maximum number of vehicles driving with full headlights per hour, at an average speed of 75 Km/h., is that of 150. This number is equivalent to a total of 300 vehicles per hour during the night on a straight stretch. Chart 1 offers guiding criteria by indicating values for traffic daily average intensity (IMD) that may be adopted to take into account the possibility of road lighting. Likewise, in order to avoid the so-called "black hole" effect, it would be convenient to consider lighting stretches between merging areas whose distance is inferior to 6 Km. in separate carriageway roads, and to 2 Km. in single carriageway roads. Besides, it would be advisable to bear in mind those road stretches where there exists a considerable percentage of accidents during the night when compared to daytime conditions. Road type Minimum IMD to illuminate (Veh/hour) Conventional roads Motorways and dual carriageways Intersections Merging areas Chart 1. IMD limit values recommended for lighting. 204 LIGHTING ENGINEERING 2002

194 Chapter 12. ROAD LIGHTING Project situations, types of lighting systems and lighting levels Project situation classification Regarding present recommendations, the following situations compiled in Chart 2 must be considered. Road type PROJECT SITUATION CLASSIFICATION Roads with separate carriageways, flyovers and access control (motorways, expresss roads). Two- way circulation road and access control (express roads) Urban traffic routes with no separation for walkways or cycle paths. 0 A2 Access roads and by- passes. Restricted urban traffic routes A3 M M Types of users S C P Project situations A1 0 TYPES OF USERS Main user M Motor traffic Other permited users S Slow moving vehicles Excluded users C Bicyclists P Pedestrians Chart Lighting class selection Once the project situation has been established according to Chart 2, lighting class is chosen. It must satisfy the illumination needs required for the mentioned project situation. The following lighting classes ME series are defined for roads on dry conditions: ME1, ME2, ME3 (a, b) and ME4 (a, b). These are established from greater to lesser need of lighting levels. Each ME series lighting class comprises the following lighting levels: - Road surface average luminance. - Luminance overall uniformity. - Luminance longitudinal uniformity. - Disability glare (increase in threshold contrast). - Environmental ratio (lighting of roadway adjacent areas). Chart 3 includes lighting classes corresponding to A project situations. Chart 4 comprises a total of 4 lighting classes ordered from greater to lesser lighting engineering need, expressing the levels as minimum values in service. This means with maintenance of installation, except for the threshold increment TI which is maximum initial value. In turn, ME3 and ME4 lighting classes are divided into a and b, whose difference lies in their longitudinal uniformity. LIGHTING ENGINEERING

195 Chapter 12. ROAD LIGHTING LIGHTING CLASSES FOR TRAFFIC ROADS PROJECT TYPES OF USER LIGHTING SITUATIONS CLASS* Roads with separate carriageways, crossings at grade and access control (highways, motorways): Traffic density and complexity of road layout: A 1 High (IMD) > 25,000 Medium (IMD) Between 15,000 and 25,000 Low (IMD) < 15,000 ME 1 ME 2 ME 3a A 2 Two- way circulation roads and access control (high speed roads): Traffic density and complexity of road layout: High (IMD) > 15,000 Medium and low (IMD) < 15,000 Urban traffic routes with no separation for walkways or cycle paths. Traffic density and complexity of road layout. Traffic control and separation of different user types. Specific parameters. Distributor roads and by- passes. Intercity roads with no access control. ME 1 ME 2 ME 1 ME 2 ME 3a ME 4a ME 1 ME 2 A 3 Traffic density and complexity of road layout. Traffic control and separation of different user types. Specific parameters. * For all project situations (A1-A2 and A3), whenever nearby areas are light (light backgrounds), all traffic roads will increase their exigencies to that of their immediately above lighting class. Chart 3 ME 3b ME 4a ME 4b Luminance is expressed in cd/m 2, whereas uniformities, understood as a ratio between luminances, lacks a unit. Disability glare appears as a percentage, and again, the environmental ratio also lacks units because it is a quotient between luminances. From the point of view of lighting engineering, the most interesting project situations are the ones belonging to group A-1. Situations for A-2 and A-3 lighting class are treated in a more general way. For A 1 project situation, Chart 3 summarizes the specific kind of lighting to be adopted, depending only on traffic intensity and road layout complexity. For the rest of project situations A 2 and A 3 there are several options to choose the kind of lighting. In each case, it is selected according to traffic intensity and road layout complexity, traffic control and separation of different kinds of users, as well as dominant specific parameters, specified below: A 2 project situation. Dominant parameters: - Crossroad type (merging areas, intersections). - Number of junctions. A 3 project situation. Dominant parameters: - Roadway separation. - Crossroad type (merging areas, intersections). - Number of junctions Lighting engineering requirements for project situations In Chart 4, lighting levels corresponding to each ME series lighting class are detailed. 206 LIGHTING ENGINEERING 2002

196 Chapter 12. ROAD LIGHTING LIGHTING CLASS* ROADWAY SURFACE LUMINANCE IN DRY CONDITIONS Average luminance Lm (cd/m2) LIGTHING CLASSES ME SERIES Overall uniformity U 0 Longitudinal uniformity U 1 * DISTURBING GLARE Threshold increase TI (%)** SURROUNDINGS LIGHTING Surrounding ratio SR*** ME ME a 0.70 ME3 b a 0.60 ME4 b *The levels for the chart are minimum values in service with maintenance of the lighting installation, except for TI, which are maximum initial values. In order maintain such service levels, a depreciation factor not greater than 0.8 must be considered, depending on luminaire type and degree of pollution in the air. ** When low luminance level sources of light are used (fluorescent tubes and low pressure sodium), a 5% threshold increase (TI) is allowed. *** The surround ratio SR must be applied to those traffic roadways where there are not other adjacent areas to the roadway with their own requisites. Chart Road lighting for wet conditions In the particular case of wet roadways, the surface reflects light in a more specular or directed way than in a diffuse one (same luminance in all directions in space). Roadway luminance uniformity is lessened negatively affecting obstacle visibility on the road. In those geographic areas where rain intensity and persistence provokes the roadway surface to be wet during a significant part of night- time hours, criteria shown in Chart 5 will be taken into account. For these recommendations, as an orientation, areas with an average higher than 100 rainy days in a year fall within this category. In these cases, calculation of luminances overall uniformity will be done according to the method described in the publication CIE nº 47 (1979), bearing in mind the photometric features of normalized pavements in that case. LIGHTING CLASS ROADWAY SURFACE LUMINANCE IN DRY AND WET CONDITIONS Average luminance Lm (cd/m2) DRY ROADWAY Overall uniformity U 0 LIGHTING CLASSES MEW SERIES Longitudinal uniformity U 1 * WET ROADWAY Overall uniformity U 0 DISTURBING GLARE Threshold increase TI (%) SURROUNDINGS LIGHTING Surrounding ratio SR MEW MEW MEW MEW * This criterion is not restrictive but may be applied, for example, to motorways, dual carriageways, two- way traffic single carriageways with access control. Chart 5 LIGHTING ENGINEERING

197 Chapter 12. ROAD LIGHTING Conflict areas Conflict areas may be defined as such due to the complexity of vision and maneuver problems that vehicles circulating on it have. Some examples are: - Junctions (merging areas and intersections), and traffic circles. - Areas where the number of lanes is reduced or the roadway width is decreased. - Areas where new lanes are merging. - Underpasses. - Overhead crossings. Likewise, conflict areas are those sectors with great difficulty because of a high presence of pedestrians, cyclists or other users of the roadway or lanes. Lighting installation must reveal or stress the conflict area, as well as all its characteristics, such as position of kerbs, pavement markings, different delineations, traffic directions, etc. Following the same policy, the presence of pedestrians, cyclists, obstacles, other vehicles and their movement in the surroundings of the conflict area must be made evident. a) Luminance criterion Whenever possible, luminance criteria, overall and longitudinal uniformities, disability glare and environmental ratios defined for different lighting classes, will be applied to conflict areas. In all cases, lighting class defined for the conflict area will be one degree higher than the degree of the roadway to which such a conflict area corresponds. For example, if a road is to be provided with an ME4 lighting class, a conflict area included in its route will need an ME3a lighting class. If several lanes meet in a conflict area, as it may happen with crossroads, the lighting class will be a degree higer than the degree of the roadway that has the highest lighting class. b) Illuminance criterion Only when luminance criteria cannot be applied, will illuminance criteria be used. This situation may take place when the sight distance is lower than 60 m. (minimum value used for luminance calculation), and whenever the observer may not be properly located due to convolution and complexity of road layout. In such situations, lighting criteria will be applied by means of average illuminance and its uniformity, which correspond to the CE series lighting classes (Chart 6). Limitations of glare or lighting pollution control, represented by G series intensity classes (Chart 7), will also be observed. LIGHTING CLASS* LIGHTING CLASS CE SERIES Average Illuminance Em (lux) Chart 6 HORIZONTAL ILLUMINANCE Average Uniformity Um CEO CE CE CE CE CE * The levels of the chart are minimum values in service with lighting installation maintenance. In order to keep such service levels, a depreciation factor not lower than 0.8, depending on luminaire type and air pollution degree, must be considered. 208 LIGHTING ENGINEERING 2002

198 Chapter 12. ROAD LIGHTING According to Chart 8, ME and CE lighting classes, with identical numbers (for example CE3 and ME3), have a similar lighting level. When the illuminance criterion is used, lighting class defined for the conflict area will be one degree higher than that of the corresponding conflict area road. For example, if a road is attributed an ME2 lighting class, a CE1 lighting class would correspond to a conflict area included in it. Supposing there is a conflict area in which there is an ME1 lighting class road merging, the conflict area will continue also as an ME1 lighting class or its equivalent, CE1. When this conflict area offers special complexity and a high risk of accidents, in the worst situation and circumstances, a CE0 (50 lux) lighting class will correspond to such an area or its similar luminance level of 3.3 cd/m 2. For intermediate situations, lighting classes ranging between the CE1 and CE0 interval may be adopted, corresponding to illuminance levels of 35, 40 and 45 lux or their similar values of 2.3, 2.7 and 3 cd/m 2, respectively. Conflict areas whose sidewalks or shoulders are not provided with a specific lighting, this will be considered as a lighting level of, at least, 50% of that foreseen for the roadway. INTENSITY CLASSES G SERIES INTENSITY CLASS MAXIMUM INTENSITY (cd/klm)** OTHER REQUIREMENTS At 70 * At 80 * At 90 * G None. G None. G None. G Intensities above 95 must equal zero. G Intensities above 95 must equal zero. G Intensities above 95 must equal zero. ** Any direction formed by the specified angle from the vertical downwards, with the luminance installed for its working. ** All intensities are proportional to lamp flux for lm. NOTE: Intensity classes G1, G2 and G3 coresspond to «semi cut-off» and «cut-off» photometric representations, concepts traditionally used for lighting requirements defined in section Intensity classes G4, G5 and G6 designate luminaires with very strong «cut-off» distribution, like for example, luminaires with glass flat closing, in any position near the horizontal of the opening or the horizontal position strictly. Chart 7 When an exhaustive requirement on glare limitation or light pollution control is needed, intensity classes G1, G2 and G3 may be adopted. Supposing the conflict area typology, due to its configuration, complexity and potential dangerousness, requires a greater glare limitation or light pollution control, only G4 and G5 intensity classes can be chosen. Only under extreme circumstances, will G6 intensity class be mandatory Layout losses Nowadays, there are no methods to quantify visual guidance provided by the installation of lighting on motor traffic roads. Nevertheless, there are certain practical considerations which may be helpful when there are layout losses. It is obvious that for safe driving, road layout, edges, possible crossroads and any other conflict area must be perfectly visible. Lighting must contribute to achieve this goal, and so, the following points must be carefully considered: - Lighting must increase road visibility with regard to adjacent areas and visibility of vertical, horizontal signaling and beacons. - Disposition of aiming points (luminaires) must allow detection of road layout, crossroads and other conflict areas beofre reaching them, marking the route. - Change in the source of light of a different colour compared to the colour of the traffic road at junctions, intersections, traffic circles, by-passes and conflict areas where the ratio between night- time and day- time accidents is high. This helps visual guidance. Regarding vision of horizontal signalling, and pavement markings, to be exact, the essential point is to secure good visibility at night, as well as for wet roadway conditions. In this case, rows of luminaires, retro reflective post mounted LIGHTING ENGINEERING

199 Chapter 12. ROAD LIGHTING delineators and contrasting pavement markings, being over the roadway water film caused by rain, maintain visibility provided by road lighting and vehicle own headlights, preserving visual guidance and road security Reference area Defined as part of the public working area, under consideration or study, several assumptions must be made according to project situation groups specified below. A project situation groups The reference area will be constituted by the totality of the motor traffic roadway width, between its edges. For double carriageway roads, the reference area will be formed by the total width of both roadways including the central reservation between the two of them, unless their width is such that each roadway may be considered separately. The width of their adjacent bands for the SR surrounding ratio, will be equal, at least, to the width of a traffic lane, 5 m width if possible. A specific requirement will be the application of such ratio around the roadway adjacent bands, according to the ME series lighting classes (Chart 4), MEW series (Chart 5) or CE series (Chart 6). If there are parallel roads next to the motor traffic road, there are two alternatives: 1) Consider the total area The reference area will be formed by the width of the motor traffic roadway, including parallel roads between their extreme edges. 2) Consider the roadway and the parallel roads separately The reference area of the motor traffic road will be exclusively the width of the roadway. The reference area of the parallel road will be only its width. For cycle paths and pedestrian areas, the reference area, apart from the width of such roads or lanes, must include 2 m. on each side Lighting classes with similar lighting levels For all project situations or A traffic roads, lighting engineering levels must be specified for each reference area. The difference between two adjacent areas should not be greater than two comparable lighting classes or those of a similar lighting level, as established in Chart 8. Once lighting levels of the ME, MEW and CE lighting classes series have been detailed, Chart 8 establishes lighting classes with similar lighting level for such series. LIGHTING CLASSES WITH SIMILAR LIGHTING LEVEL CE 0 ME 1 MEW 1 CE 1 COMPARABLE BY COLUMNS ME 2 MEW 2 CE 2 ME 3 MEW 3 CE 3 Chart 8 ME 4 MEW 4 CE 4 ME 5 MEW 5 CE 5 For ME/MEW classes r-chart C 2 roadway surface reflectance (Publication CIE nº 66) ME LIGHTING ENGINEERING 2002

200 Chapter 12. ROAD LIGHTING Lighting class temporal variations In order to save energy in all project situations, lighting class may be momentarily changed to another one with an inferior level of lighting engineering at certain hours at night during which traffic intensity is fundamentally lower. This can be done by means of the corresponding regulation of the lighting level system. Lighting class temporal variations should not be done in conflict areas. When lighting level is reduced, that is to say, it is changed from one lighting class to another at a certain hour, (midnight lights out), changes will be such that, if average luminance is reduced to a lower class (for example, go from M2 to M3), glare and luminance uniformity criteria established in Chart 4 must be observed High mounting support lighting This name is given to lighting through aiming points whose mounting height is higher than 16 m., and whose maintenance cannot be performed with a vehicle provided with a hydraulic basket. This system is used each time the use of lighting conventional solutions is not satisfactory, due to the handling of supports and to the difficulty of their installation in their corresponding location. Lighting by means of high mounting supports is related to lighting of large surfaces, and is usually applied, in the following situations, among others: - Complex motorways, dual carriageways or road junctions. - Traffic circles. - Toll areas. Lighting installation by means of high mounting supports is a solution when the installation of classic shafts or columns originates problems in the surroundings, such as: - Loss of perspective and level separation between supports (crossroads of motor traffic roads at different levels). - Dimensioning problems (large areas), or aesthetics and visual guidance confusion (multiplicity of supports). For this type of lighting the most frequent installation heights are 30 and 35 m. supports, even though in concrete situations like complex crossroads, they may be higher than 40 m. The number of lighting sources will be reduced as much as possible, by using discharge lamps with high lighting efficacy and potency. Luminaires provided with a conventional, adjustable or specific optical system as well as floodlights may be installed, always paying attention to convenient solutions to achieve the established goals. In order to perform maintenance operations, accessibility to luminaires, control gears and lamps will be done by means of fixed scales attached to the supports, up to a height of 20 m. For higher columns, the installation of an impeller system is convenient. In order to decrease glare, the tilt angle of floodlight maximum intensity will amount to 65%, limiting, as far as possible, intensity values above this angle. Besides, the installation of grids or other antiglare devices may also be contemplated. LIGHTING WITH HIGH SUPPORTS. LIGHTING CLASSES DESCRIPTION OF ROAD TYPE LIGHTING CLASSES Very complex crossings with high traffic density and complex road layout and field of vision CE 0 Complex crossings, traffic circles CE 0 CE 1 Toll areas CE 2 NOTE: In lighting situations corresponding to very complex crossings with high traffic density and complex road layout and field of vision, in some special cases, luminance average uniformity will be 0.5. Chart 9 LIGHTING ENGINEERING

201 Chapter 12. ROAD LIGHTING Lighting engineering calculations Luminance calculation of lighting installation Method Luminance at a point of the roadway is calculated using the following formula: L = r (β, tgγ) (cm/m E Ι (c, γ) 2 ) R h 2 where the sum ( ) comprises, in theory, all luminaires in the installation. Luminous intensity values (I(c, )) and reduced luminance coefficient (r(, tg )) are obtained by square interpolation of the luminaire intensity matrix and the pavement reflection chart. Lastly, variable h is the luminaire maximum height (Fig. 1). Q h γ T Observer α s δ P β Figure 1. Luminance at a point. Calculated luminance values are influenced by the maintenance factor as decreasing, which takes into account the lamp luminous depreciation caused by dirtiness. In all calculations, a value lower or equal to 0.8 will be adopted, depending on luminaire type and local degree of atmospheric pollution Hypothesis The following sections are applicable to straight roadway stretches or large radius curves (radius >= 300 m.). In another kind of configuration, each case will be studied separately, applying certain criteria for special situations. Moreover, as it has already been indicated, calculations are established for pavement in dry conditions Selection of calculation lattice The lattice calculation is the set of points in which luminance values will be calculated. In a longitudinal sense, the lattice will cover the stretch of roadway between two consecutive luminaires in the same side. In a transversal sense, it must comprise the width defined for the reference area. Calculation points will be distributed as shown in Fig. 2 and their number will be: - From a longitudinal point of view: 10 points for separations between luminaires lower than 50 m., or the least 212 LIGHTING ENGINEERING 2002

202 Chapter 12. ROAD LIGHTING number of points that will provide distances equal or inferior to 5 m. between them, for separations between luminaires higher than 50 m. - From a transversal point of view: 5 points per lane, one of them located in its center. The two most external points will remain inside the roadway, with respect to its edge, at 1/6 of the lane width. Luminaire Luminaire a/2 a a/6 : Lattice point Figure 2. Calculation lattice Observer s position a) Height: 1.5 m. over the roadway surface. b) Longitudinal situation: At 60 m. from the first transversal line of calculation points. c) Transversal situation: - For the calculation of average luminance and overall uniformity, the situation will be at 1/4 of the roadway total width, measured from the right edge of the roadway. - For the calculation of longitudinal uniformity, for roads with traffic in two directions, the situation will be in the center of each of the lanes of the direction under study Number of luminaires The number of luminaires that contribute to luminance of a calculation point must be restricted to those previously located at five times their mounting height, and at twelve times their mounting height, in the circulation sense. Likewise, as for luminaires placed in a transversal way to the direction of circulation, only those which are at 5 times less than their mounting height will be taken into account Calculations - Average luminance: luminance average value calculated in the lattice points. - Overall uniformity: quotient between the minimum luminance calculated in a lattice point and its average luminance. - Longitudinal uniformity: for each of the lanes, it is obtained by dividing minimum and maximum exact luminance calculated on the axis of the lane. LIGHTING ENGINEERING

203 Chapter 12. ROAD LIGHTING Calculation of horizontal illuminances Method Horizontal illuminance at a point of the roadway is calculated using the following formula: E = E Ι (c, γ) cos3 γ h 2 R (lux) γ being the angle formed by the direction of incidence at the point with the vertical (Fig. 3). The sum ( ) comprises, in theory, all luminaires in the installation. a E = dφ ds h γ I P C Figure 3. Illuminance at a point Illuminance calculations, as that of luminances, will be affected by a maintenance factor lower or equal to 0.8, depending on the type of luminaire and the local degree of atmospheric pollution Selection of calculation lattice The same as described in section will be used Number of luminaires Illuminances produced by luminaires will accumulate in the lattice points little by little, evolving from the closest to the furthest ones, up to a point in which a luminaire will not produce a level higher than 1% of the accumulated value in any of the lattice points Calculations - Average illuminance: average value of illuminances calculated in the lattice points. - Average uniformity: quotient between minimum illuminance calculated at a point of the lattice and average illuminance. - Extreme uniformity: quotient between minimum and maximum illuminances calculated at a point of the lattice Disability glare calculation Method It is based on the calculation of veiling luminance: 214 LIGHTING ENGINEERING 2002

204 Chapter 12. ROAD LIGHTING L v = Σ ( E g ) (cd/m2 ) θ 2 where Eg (lux) is the illuminance produced by the eye in a plane perpendicular to the line of vision, and θ (rad) is the angle between the direction of light inciding in the eye and the observation direction. The sum ( ) is extended, in principle, to all luminaires of the installation (see ). The increase of the perception threshold is calculated according to the following formula: L v TI = (in %) (L m ) 0.8 which is a valid formula for roadway average luminances (Lm) between 0.05 and 5 cd/m Shielding angle For disability glare calculation purposes, luminaires whose observation direction forms an angle greater than 20 with the vision line will not be considered, since they are shielded by the roof of the vehicle Observer s position a) Height: 1.5 m. over the roadway surface. b) Longitudinal situation: in such a way that the closest luminaire to be considered in the calculation will formed exactly a 20 angle with the vision line. For staggered dispositions, two different calculations will be done (with the first luminaire on each side at 20 ). The highest value of the two will be the result provided. c) Transversal situation: at 1/4 of the roadway total width, measured from its right edge. d) Observation point: The observer always looks at a point on the roadway placed at 90 m. in front of him, in the same transversal situation in which he finds himself. Shielding plane 20º Ig P θ α=1º O W 1/4W Figure 4. Observer s position. LIGHTING ENGINEERING

205 Chapter 12. ROAD LIGHTING Number of luminaires All luminaires placed at less than 500 m. from the observer are considered to contribute to disability glare Calculations - Veiling luminance: for each row of luminaires, the closest one is first considered, progressively driving away and accumulating veiling luminances produced by each of them until their individual contribution is lower than 2% of the accumulated one. The maximum is up to luminaires located at 500 m. from the observer. Finally, veiling luminance of all rows of luminaires will be summed. - Increase in perception threshold: it will be calculated with veiling luminance values obtained according to and with average luminance according to Lighting systems Distribution of aiming points in crossroads, traffic rounds and curves In crossroads and intersections lighting levels will be those established for conflict areas and, at least, from a 10 to 20% higher than those corresponding to the road class whose lighting level is higher between those that merge in the same point. Consequently, the situation of aiming points will be ideal in order to achieve such mentioned levels. By way of an example, ground plan dispositions are indicated in Figs. 5 and 6. Figure 5 Walkway Walkway Walkway Walkway Walkway Walkway Roadway Walkway Walkway Roadway Walkway Figure 6 H mounting height of aiming points (Figs. 7 and 8) must be equal to that of the points of the main road that merges in the traffic round to be illuminated. In case the central area of the traffic round lacks lighting higher or equal to 1.5 times the main roadway average illuminance, supplementary lighting will be required. 216 LIGHTING ENGINEERING 2002

206 Roadway Roadway Chapter 12. ROAD LIGHTING Walkway Walkway Roadway Walkway Roadway Figure 7 Walkway Walkway Roadway Walkway Roadway Figure 8 If the central part of the traffic round has a diameter lower than 18 m., a special aiming point in a column or multiple arm shaft will be installed in its center (Fig. 7). If its diameter is greater than 18 m. or it has trees in the center, aiming lights will be placed in the prolongation of the circulation axis (Fig. 8). With regard to installation of aiming points in curves and in relation to lighting, curve stretches are considered those whose radius is inferior to 300 m. When their radius is greater than such a figure, they will be considered as straight stretches. If the width A of the traffic road is lower than 1.5 times its mounting height H, aiming points must be installed in the outer part of the curve, locating an aiming point in the prolongation of the circulation axis (Figs. 9 and 10). Separation between aiming points will be inversely proportional to the radius of the curve, varying between 3/4 and 1/2 of the calculated average separation of a straight stretch of such a traffic road. For traffic roads whose width is greater than 1.5 times their mounting height H, the installation of aiming points must be twosided coupled. In any case staggered distribution must be avoided. Walkway Roadway Roadway Figure 9 LIGHTING ENGINEERING

207 Chapter 12. ROAD LIGHTING Walkway Roadway Walkway Figure Installation of aiming points in straight stretches For traffic roads in straight stretches, five basic types of distribution of aiming points will be considered One- sided When aiming points are situated in a single side of the traffic road (Fig. 11). It will generally be used when the A width of the roadway is equal or inferior to the mounting height H of the luminaires. Walkway H Roadway A A Walkway S Figure 11. One- sided installation Two- sided staggered When aiming points are located in both sides of the traffic road staggered or alternate (Fig. 12). It will generally be used when the A width of the roadway is 1 to 1.5 times the mounting height H of the luminaires. The 1 to 1.3 H interval is ideal. Walkway H Roadway A A Walkway S Figure 12. Two- sided staggered installation Two- sided coupled When aiming points are located in both sides of the traffic road, one opposing the other (Fig. 13). It will generally be used when the A width of the road is greater than 1.5 times the mounting height H of the luminaires. It is more adequate to use it when the width is greater than 1.3 times the height H. 218 LIGHTING ENGINEERING 2002

208 Chapter 12. ROAD LIGHTING Walkway H Roadway A A Walkway S Figure 13. Two- sided coupled installation Central or double row In traffic roads with a central reservation between the two directions of traffic, aiming points will be installed in doublearmed columns or shafts, located in the central reservation, when its width ranges between 1 and 3 m. (Fig. 14). Walkway Roadway Direction of traffic Central reservation b Direction of traffic Roadway Walkway Figure 14. Installation for values 1 < b < 3 m. For central reservations, wider than 3 m., double-armed shafts will not be used. In any case, their disposition will be studied as if we were talking of two separate and independent roadways, giving rise to the installation of the following figures. Fig. 15 is recommended over Fig. 16, since drivers are incited to circulate always on the traffic lane nearest to the central reservation (left lane). Walkway Roadway Direction of traffic Central reservation b Direction of traffic Roadway Walkway Figure 15. Installation for any b value. LIGHTING ENGINEERING

209 Chapter 12. ROAD LIGHTING Walkway Roadway Direction of traffic Central reservation b Direction of traffic Roadway Walkway Figure 16. Installation for values b > 3m Catenary Aiming points are fixed axially to the catenary longitudinal cables, lying between two solid supports installed in the central reservation and located at a great distance one from the other, at about 50 to 100 m. (Fig. 17). Figure 17. Catenary installation. This type of distribution has a very serious inconvenience which is that aiming points are easily moved by the action of the wind, losing some of their effectiveness. 220 LIGHTING ENGINEERING 2002

210 Chapter 12. ROAD LIGHTING Combined groupings Different combinations of the five basic dispositions (one- sided, staggered, two- sided, central and catenary) may be used. For example, in two roadway roads with a central reservation, it is usuall to combine central and two- sided installations in opposition (Figs.18 and 19). Walkway Slow moving traffic roadway (2 lanes) Direction of traffic Central reservation Direction of traffic Fast moving traffic roadway (3 lanes) Central reservation Fast moving traffic roadway (3 lanes) Roadway Direction of traffic Central reservation Slow moving traffic roadway (2 lanes) Direction of traffic Walkway Figure 18. Combined grouping. Walkway Slow moving traffic roadway Direction of traffic Central reservation Direction of traffic Fast moving traffic roadway Direction of traffic Central reservation Slow moving traffic roadway Direction of traffic Walkway Figure 19. Combined grouping. LIGHTING ENGINEERING

211 Chapter 12. ROAD LIGHTING Disposition of aiming points in elevation For disposition of aiming points in elevation, the height adopted will be mounting height H chosen in lighting engineering calculations. However, there are special instances in which mounting height must be fixed according to other concepts, as it happens with traffic roadways with trees near the edges. If trees have an enormous size, they can be cleared up to a height of 8 or 10 metres. Luminaires will be placed at such height (Fig. 20) mts. Figure 20. Elevation of enormous trees. If trees have a small size, luminaires will be placed at a height of 12 to 15 metres (Fig. 21). In any case, it is convenient to give trees an adequate pruning periodically mts. Figure 21. Elevation of small trees. 222 LIGHTING ENGINEERING 2002

212 Chapter 12. ROAD LIGHTING Disposition of aiming points in intersections Intersections in right angle with two illuminated roadways Two cases must be distinguished for this type of intersections: whenever motor traffic on roadways is not canalized (Figs. 22 to 25), and whenever motor traffic on only one of the roadways is canalized by means of small directional traffic islands (Fig. 26). When motor traffic on roadways is not canalized, the problem must be tackled by combining installations recommended for each type of lighting (one- sided, staggered, double row, two- sided, etc.), as represented in Figs. 22 to 25. Aiming points drawn in intersections in white serve as the basis for installing the rest. e e1 e1' < e1 e1 e' < e e e = normal separation e' = reduced separation Right angle intersection: Recommended installation on two roadways with one- sided lighting Figure 22 e e1 e1' < e1 e1 e' < e e e = normal separation e' = reduced separation Right angle intersection: Recommended installation on two roadways with staggered lighting Figure 23 LIGHTING ENGINEERING

213 Chapter 12. ROAD LIGHTING e e = normal separation e' = reduced separation e' < e e1 e1' < e1 e1 e Right angle intersection: Recommended installation on two roadways with one- sided and two- sided lighting Figure 24 e e = normal separation e' = reduced separation e' < e e1 e1' < e1 e1 e Right angle intersection: Recommended installation on roadways with staggered and two- sided lighting Figure 25 In the second case, when motor traffic in one of the roadways is canalized by means of small directional traffic islands whereas, traffic is not in the other, (Fig. 26), the installation of aiming points must begin with the roadway provided with traffic islands, which will be studied separately. The installation of aiming points will begin from the intersection, reducing the separation between these and continuing with the roadway with canalized traffic, adopting any of the adequate installation systems (one- sided, staggered, double row, two- sided, etc.). The origin of locating aiming points for roadway lighting wherever traffic is not canalized by means of traffic islands will be also tackled at the intersection, adjusting aiming points as established for the other roadway, and continuing with an adequate placing of aiming points bearing in mind the roadway characteristics (one- sided, staggered, double 224 LIGHTING ENGINEERING 2002

214 Chapter 12. ROAD LIGHTING row, two- sided, etc.). Eventually, lighting in the center of the intersection may be reinforced by installing more powerful aiming points, by adopting more powerful lamps or installing two luminaires in every aiming point or support. "X"- shaped intersection: It may turn useful to provide circled aiming points with more power Figure "T"- shaped intersections between two illuminated and partially canalized roadways This type of intersections (Fig. 27) establishes an installation of aiming points recommended so that users who arrive from the merging roadway are able to see an illuminated background ahead of them. This is not the only possible solution, though. Depending on local conditions, it may be possible to reduce the number of aiming points, using others of a higher potency and height installation (Fig. 28). "T"- shaped intersection: Installation example. Double lined areas represent the visual guidance effect that must be provided by lighting. It may turn useful to provide circled aiming points with more power. Figure 27 LIGHTING ENGINEERING

215 Chapter 12. ROAD LIGHTING 60 m. "T"- shaped intersection: Installation example with aiming points of more power and of height supports than those of figure Aiming point of 18 m. with 4 luminaires. Aiming point of 18 m. with 2 luminaires. Aiming point of 12 m. with 1 luminaire. Aiming point of 12 m. with 2 luminaires Figure "Y" or "T"- shaped intersections between two roadways totally canalized In the proximity of such intersections, generally both traffic directions for vehicles are separated by large directional traffic islands, along which the layout of aiming points is one- sided (Fig. 29). Likewise, more powerful and aiming points of a greater height may be placed (Fig. 30). "Y" or "T"- shaped intersection: Example of a one- sided installation on two important roadways totally canalized by means of traffic islands Figure LIGHTING ENGINEERING 2002

216 Chapter 12. ROAD LIGHTING 50 m. 50 m. 50 m. 50 m. "Y" or "T"- shaped intersection: Example of a one- sided installation with aiming points of more power and height than those of figure Figure Vegetation Understanding and cooperation between vegetation and lighting is required so that neither interferes with the job or function performed by the other. luminaire Mounting height A Pruning line D M Pruning line angle "A" Tree pruning height M = 0.36 D M = 0.26 D M = 0.17 D Figure 31 LIGHTING ENGINEERING

217 Chapter 12. ROAD LIGHTING The selection of the type of shrub or tree must be based on those which leave enough free space for lighting with minimum interference between both of them. These selections may include trees with stylized, spherical or normal forms. In most cases, a good pruning service may solve any problem between trees and road lighting. It must be highlighted that even in installations with a great mounting height, it is not necessary to prune all trees up to the luminaire height. It is only necessary to prude those branches which fall below the useful luminous beam (Fig. 31). Leafiness of trees located between the luminaire and the objects, may serve the purpose of trimming and distinguishing silhouettes in an intentioned way. At the same time, it helps to reduce luminaire direct glare on possible observers or drivers. This advantage is particularly important in roads with local traffic and residential areas, where relatively high inter- distances, together with high potencies and angles approaching the horizontal are required Criteria and design compromises To minimize lighting interferences with trees, there are certain types of compromises which may be applied to lighting systems. Regarding this respect, possible variations that may happen in inter-distance, mounting height, and transverse situation of aiming points must be born in mind. Such variations generally produce, in turn, changes in the luminous distribution of the lighting installation Design modifications As a modification example, mention the fact that all luminaires may be mounted on long arms. This usually increases the installation expenses, but improves lighting effectiveness, avoiding or palliating interference with vegetation. Spherical type Oval type Cylindrical type Walkway Wide pyramidal type Narrow pyramidal type Roadway luminaire mounting height mts Luminaire projection mts. Figure 32 Another possible design modification may be luminaire suspension by means of catenary systems over the center of the roadway. In this case, the problem is the extra expenses implied by the utilization of two supports per luminaire. An added disadvantage to this system is the loss of lighting efficacy which takes place when luminaires are under the action of the wind, given that the wind modifies their orientation and, therefore, also their photometric distribution. Another possible design variation consists in reducing the luminaire installation height under vegetation, in such a way that also lamp potency is reduced. The problem is also that of extra expenses, since the interdistance between luminaires has to be reduced. Therefore, the number of luminaires must be increased and advantages disappear. One last design alteration may be performed, which consists in increasing lamp potency to compensate for light lost on its way towards roadway and sidewalks. However, this presupposes a clear inconvenience since the luminaire 228 LIGHTING ENGINEERING 2002

218 Chapter 12. ROAD LIGHTING direct glare increases and, above all, energetic cost is also higher without resulting in a clear improvement of luminous uniformity Design fundamentals When variations in the longitudinal inter- distance of aiming points is performed so that they do not interfere with trees, deviations of ±10% of the previous calculated separation may be assumed. Such variations do not imply great differences as far as results are concerned. Maximum differences of about 20% of the interdistance may be tolerated, provided it does not happen in two consecutive aiming points. Such variation, anyway, may be proved through calculations which will indicate whether all exigencies established beforehand are verified or not for those areas affected by modification. When separation of two or more consecutive luminaires is altered, it must be confirmed by means of variation of other parameters, like transverse location of aiming points or their installation height. Luminaire alingment over the roadway is a basic factor with respect to visibility and installation aspect or appearance. Only when it is not possible in any other way, a luminaire will be installed outside the line of the others. The height of columns or shafts which support luminaires will be selected in such a way that it will be adequate to each installation in particular. The higher these supports are, the fewer problems will be encountered with leafiness of vegetation, but it is also true that expenses will probably grow in a considerable way Design data Figs. 32 and 33 aim at being a practical guide when this kind of difficulties between lighting and tree leafiness appear. For example, a luminaire transverse situation for different heights and vegetation types. Walkway side Rodway side type Narrow pyramidal Cylindrical type Spherical Wide pyramidal type Luminaire projection in mts. Dist. from luminaire to vegetation type Spherical type Wide pyramidal type Cylindrical type Narrow pyramidal type Figure 33 Although roadway lighting usually produces interferences with vegetation, lighting of walkways of other lateral areas of the roadway must not be forgotten. This aspect is sometimes even more important than roadway lighting itself in certain residential or pedestrian areas. LIGHTING ENGINEERING

219 Chapter 12. ROAD LIGHTING In order to solve this problem three factors may be changed, namely: - Luminaire installation location and height. - Correct and regular pruning. - Addition of an aiming point exclusively for the lighting of these areas, at a lower height than road conventional lighting. 230 LIGHTING ENGINEERING 2002

220 Chapter 13. TUNNEL LIGHTING 13.1 General remarks Long tunnel lighting Lighting of short tunnels and underpasses Emergency lighting Maintenance Ignition control Night- time lighting (tunnel exterior zone) Tunnel lighting design Visual guidance LIGHTING ENGINEERING

221 232 LIGHTING ENGINEERING 2002

222 Chapter 13. TUNNEL LIGHTING General remarks Vehicle driving through tunnels during day- time hours gives rise to a totally different problem when compared to night- time outdoor driving, which is basically reduced to differences existing between high outdoor luminance levels and low luminance levels in the interior of tunnels. The fundamental visual problem in tunnels is that of adaptation of the human eye from high outdoor luminances during the day, to low luminances (virtually null) in the interior of a tunnel. It must also be born in mind that, for a certain luminance distribution, an obstacle cannot be seen if its luminance is much lower than the distribution luminance. All this provokes what is called "the black hole effect" which prevents drivers from seeing the interior of the tunnel during the day, when they are at a certain distance from its mouth. All this considering that for the majority of tunnels, day- time natural light only enters, depending on their orientation, some distance of about one to three times their longest transversal dimension. Beyond such a distance, existent luminous conditions are not enough to secure visibility of eventual obstacles, or for an adequate guidance of drivers. From the point of view of lighting engineering, the following zones may be differentiated in tunnels: access, entrance constituted by the zones of threshold and transition, interior and finally, exit (see Fig. 4). Due to economic reasons, it is not possible to establish lighting conditions identical to those existing during the day in the outside (access zone) in the tunnel entrance zone, which may reach values of up to lux. In the threshold zone located just at the entrance of the tunnel, with an approximate length equal to the security distance, lighting during the day must be measured in such a way that it will secure enough vision of eventual obstacles on the roadway. Although a first brusque reduction of lighting levels existent outside (access zone) takes place, it is acceptable. In the second part of the threshold zone, lighting levels progressively diminish Visual problems in tunnels Visual problems in tunnels comprises induction and adaptation effects, as well as the influence of veiling luminances. All this requires to bear security distance in mind depending on tunnel traffic speed Induction effect Human eye sensitivity depends on the distribution of luminances in the field of vision. Sensitivity is also influenced by two phenomena called induction and adaptation. Regarding induction, it is the effect produced by the influence of adjacent parts of the retina to that in which the image of the object being seen is formed. If the driver s eyes are in a state of adaptation to a certain distribution of luminances, this person can only see those objects whose luminance is close to the mentioned distribution. Due to the eye adaptation of a driver who is approaching a tunnel to high daytime exterior luminances, when the driver observes the mouth or entrance of the tunnel, the part of the retina receiving the image from outside influences the other part receiving the image of the tunnel entrance, thus, creating an effect of induction. Hence, the tunnel entrance appears as a black hole in which not a single detail can be seen. The induction effect makes that with a given distribution of luminances (natural daytime road lighting), an object cannot be seen if its luminance is much lower than the distribution one (virtually null lighting at the tunnel entrance), no matter how long such an object is contemplated Adaptation effect It allows the adjustment of the human eye sensitivity to a change in the distribution of luminances in the field of vision. The time required for the adaptation of the human eye sensitivity to a change in the distribution of luminances, is known as adaptation time. The adaptation of the eye sensitivity to quick changes in the distribution of luminances in the field vision is not instantaneous. For a certain amount of time, visual capacity decreases, giving rise to a momentaneous blindness in case of a brusk change in the distribution of luminances. That is to say, in some situations like the case of tunnel entrances, the problem may be serious and visual function may not be possible. LIGHTING ENGINEERING

223 Chapter 13. TUNNEL LIGHTING Influence of veiling luminances Parasite light present on the drivers eyes (foveal veiling luminance or Fry s), the atmospheric situation (atmospheric luminance) and reflexes on the vehicle winshield (windshield luminance), are combined to form a luminous veiling that reduces visibility of obstacles at the entrance of tunnels. The main reason for tunnel lighting is to secure visibility of obstacles at any time, which requires to perceive a difference between luminance of the obstacle and luminance of the background or tunnel roadway and walls. By definition, contrast is expressed in the following way: C = L 0 L f L f where: L 0 = Luminance of the obstacle. L f = Luminance of the background. Contrast C may be positive or negative: If L 0 > L f C > 0 Positive contrast (obstacle lighter than background) If L 0 < L f C < 0 Negative contrast (obstacle darker than background) In the case of tunnels, two types of contrast must be distinguished: the so- called intrinsic or physic C int measured next to the obstacle and the retina contrast C R measured from the vehicle driver s eye. In Fig. 1, it may be checked that intrinsic contrast C int is measured next to the obstacle in (1), while retina contrast C R is evaluated from the observer s eye in (4). Between both contrasts, a set of veiling luminances called atmospheric L atm, of windshield L pb and foveal or Fry s L v, respectively, which give rise to veiling glare which discomforts vision in the driver s eyes. The layers of air in the atmosphere containing particles illuminated by sunlight give rise to atmospheric luminance L atm due to the refraction of light in such air layers of the atmosphere. This type of luminance depends on atmospheric conditions and the position of the sun. Luminance of the windshield L pb is produced as a result of the existence of windshields in vehicles, which provokes difraction or reflection effects depending on the position of the sun in the visual field and the state, curvature and inclination of the windshield itself. Foveal veiling luminance or Fry s L v is caused by the discomfort in vision provoked by a luminance not belonging to the visual task to be perfomed. This also difficulties the perception of images of such a visual task, due to the luminous veil produced in the driver s eye as a result of the difraction of light in the aqueous humor of the eye globe. Atmospheric windshield and foveal or Fry s veiling luminances produced between the obstacle and the driver, as shown in Fig. 1, reduce the intrinsic contrast C in of the obstacle (C R < C int ) without changing the sign of the contrast, decreasing visibility of obstacles at the entrance of tunnels. Such a reduction in the intrinsic contrast may cause that visibility of obstacles at the entrance of tunnels is not secured, above all in the case of strong veiling luminances, which may oblige to duplicate luminance values to be reached in the tunnel threshold zone by means of artificial lighting. The aim is to soften reduction of the mentioned contrast. Consequently, a decrease of the visibility of obstacles on the part of the driver may take place. Thus, the effect produced by veiling luminances is taken into account when establishing lighting levels at the entrance of tunnels. Parasite or veiling luminances which characterise the effects of the surroundings of the tunnel, the windshield and the atmosphere and bother the driver s vision are variable according to the region and zone where the tunnel is located. They also depend on its orientation, season, climate, hour of the day, etc. 234 LIGHTING ENGINEERING 2002

224 Chapter 13. TUNNEL LIGHTING 2 Atmosphere 3 4 Windshield Foveal or Fry's veil 1 LO Cint. = - Lf Lf LOR CR = - LfR LfR Atmospheric parasite veils Latm of windshield Lpb and of foveal veil or Fry's Lv Figure Security distance Security distance (DS) is defined as the necessary distance for the driver of a vehicle circulating at a certain speed to stop before an obstacle on the roadway is reached. Such a distance consists of two addends: the vehicle travel from the moment in which the driver sees the obstacle until this person brakes, and the breaking distance as such. Security distance may be calculated according to the following formula: DS = RT V 1 0 v g! dv f 1 (v) + h where: DS = Security distance (m.). V 0 = Design speed (Km/h.). RT = Perception- reaction time (s). f 1 (v) = Friction coefficient (longitudinal) dependent on v. g = Gravity acceleration (9.81 m/s 2 ). h = Slope or gradient inclination of the road (%). Applying the formula, the following examples of stopping distance DS on flat roads for retardations from 3.5 to 5 m/s 2 are obtained: Design speed (Km/h) Ret DS (wet road) m DS (dry road) m Chart 1 When a vehicle is close to a tunnel, the induction and adaptation effects and the influence of veiling luminances are intimately related to the distance at which the driver of the vehicle is at the entrance of such a tunnel, in the so-called access zone with an approximate length equal to the security distance (DS, Fig. 4). The higher the speed of a vehicle, the higher the security distance (DS). This is the reason why some considerations must be taken into account: - Perception of an obstacle is proportional to the inverse of the square of the security distance (DS -2 ), supposing contrast is constant. - Atmospheric veiling luminance L atm is proportional to the security distance (DS). Atmospheric transmission is T atm = 10 -k DS. -Visual adaptation speed is related to the vehicle approximation speed. LIGHTING ENGINEERING

225 Chapter 13. TUNNEL LIGHTING For a driver in the access zone, the higher the speed of the vehicle, the longer the distance from the entrance of the tunnel towards the interior in which the driver has to see inside the tunnel. This presupposes greater length of the threshold zone to be illuminated. Likewise, the greater the distances, an obstacle located in the interior of the tunnel requires a smaller angle in the driver s eye and, thus, it is less visible. Besides, the air layer between the driver located in the access zone and the entrance of the tunnel is greater, which means greater atmospheric luminance L atm, reduction of intrinsic contrast C int and, consequently, decrease of visibility of obstacles. All this requires higher lighting levels in the threshold zone of the tunnel. In short, higher speeds require longer security distances (DS), which means greater length of the threshold zone of the tunnel to be provided with lighting, as well as higher lighting levels in such a zone. Therefore, due to both reasons, higher costs come along Lighting systems Lighting systems in tunnels may be divided into two families: symmetrical and asymmetrical, which, at the same time, comprises a lighting system with flux opposite to vehicle circulation directions. This also receives the name of counterflux. The lighting system favoring the flux lacks practical utility and, therefore, is not considered. Lighting of tunnels is characterized by the contrast quality parameter P, also known as contrast development coefficient q c whose formula is the following: P = q c = L E v... where: L = Roadway luminance in cd/m 2. E v = Obstacle vertical illuminance in lux at the roadway level in the direction of traffic. That is to say, average illuminance on a vertical surface perpendicular to the axis of the tunnel, and oriented towards the entrance Symmetrical lighting system The symmetrical lighting system is that in which luminaires have a distribution of luminous intensity which is symmetrical in relation to the plane C 90º / 270º. To a plane perpendicular to the axis of the tunnel, as represented in Fig. 2. Contrasts of obstacles may be negative or positive, depending on the reflection properties of their surface. Nevertheless, this system strives to secure vision on a positive contrast: obstacles will be seen as light against the dark background of the tunnel roadway and walls. The symmetrical lighting system is used in all cases in the interior zone of tunnels with luminaires provided with conventional and compact fluorescent lamps, high and low pressure sodium lamps or discharge by induction lamps. The installation of such a system is possible in the entrance zone of such tunnels which have established a low limitation in the approximation speed of vehicles. This system allows good visibility of obstacles and lack of glare. From a photometric point of view, it is advisable that the roadway pavement and the tunnel walls are diffusing surfaces (low specular factor S 1 ) and light (high average luminance coefficient Q 0 ). Therefore, it is convenient that pavement belongs to the R1, R2 or C1 Class, following recommendations of the C.I.E., with a high degree of brightness or luminosity (Q 0 is the highest possible). 236 LIGHTING ENGINEERING 2002

226 Chapter 13. TUNNEL LIGHTING Figure 2 The measuring of tunnel lighting, by means of a symmetrical system in the entrance zone leads to lighting levels difficult to achieve for approximation speed of vehicles higher than 90 Km/h with weak or average veiling luminances in the access zone, or higher than 70 Km/h with strong veiling luminances. When levels higher than 200 cd/m 2 are to be achieved, very complicated to reach in practice with the symmetrical system, it is necessary to find other alternatives in such situations, either limitation of the speed of vehicles or installation of a lighting system at counterflux in the entrance zone Counterflux lighting system The counterflux lighting system is a system in which luminaires have a distribution of asymmetric luminous intensity, directed against the direction of traffic, as represented in Fig. 3. This lighting system favours seeing obstacles by negative contrast. Obstacles are highlighted as dark against the roadway light background and tunnel walls, due to the fact that vertical illuminance in planes facing approaching drivers is low. This vision in negative contrast is achieved reducing the obstacle luminance (L 0 ), slightly limiting its vertical illuminance (E v ), and increasing roadway luminance. LIGHTING ENGINEERING

227 Chapter 13. TUNNEL LIGHTING Figure 3 The counterflux lighting system is only used in the tunnel entrance zones. It is recommended in this zone where the limitation of the vehicle speed is high, that is to say, from approximately 90 Km/h, given economic advantages found in these situations. Luminaires are to be installed over traffic lanes and are normally equipped with high pressure sodium lamps. It must be stressed that counterflux lighting is never installed in the interior zone of tunnels. Due to the own structure of the system, its installation must be avoided in two- way tunnels (bidirectional), because in this case, what is counterflux for one determined direction of traffic would be favourable for the opposite one, thus, modifying drivers visual conditions. The counterflux lighting system usually creates more contrast between the obstacle and the background, but it can also produce a certain increase in the black hole effect, reducing drivers visual comfort. Likewise, such a counterflux system may not be appropriate for the entrance of tunnels with high daytime light, and it is even less effective when traffic intensities are very high or a high percentage of slow moving vehicles is foreseen. In this lighting system which provides good visibility of obstacles, glare must be limited controlling luminous intensity emited by luminaires. The use of specular pavement (high specular factor S 1 ) and light is advisable, from a photometric point of view. That is to say, with a high average luminance coefficient Q 0, pavement class R3, R4 or C2, according to recommendations of the C.I.E., with a high degree of brightness or luminosity (Q 0 is the highest possible). Besides, a high luminance must be limited in tunnel walls, at least, up to a 1 m. level, with the aim of reducing obstacle vertical illuminance (E v ) Contrast development coefficient The adopted lighting system either symmetrical or counterflux is characterized by certain contrast development coefficients q c, whose values are included in Chart LIGHTING ENGINEERING 2002

228 Chapter 13. TUNNEL LIGHTING Lighting systems CONTRAST DEVELOPMENT COEFFICIENT Contrast development coefficient q c = LIE v Symmetrical 0.2 Counterflux 0.6 Note: Lighting systems whose values for contrast development coefficient is between 0.2 and 0.6 have not been taken into account. Chart 2 The value of the contrast development coefficient q c = L/E v is slightly linked to the intrinsic characteristics of the tunnel lighting system, to the installation of luminaires and the reflective characteristics of the pavement, as well as to the photometric contribution of the tunnel walls. These values of Chart 2 characterize the lighting system of tunnels only in night- time measures, that is to say, without influence of day- time light, which alters values of the contrast development coefficient q c. In measurements during the day in the entrance zone of tunnels and for the symmetrical lighting system, q c reaches figures higher than 0.2, whereas for the counterflux system, qc values are lower than 0.6. Especially, due to this variation in the contrast development coefficient q c = L/E v during a day- time measurement respect to a night- time measurement, contrast changes sign going from negative to positive contrasts and viceversa. This gives rise to situations in which obstacles are not perceived Natural lighting system with daytime light Besides artificial lighting systems and counterflux ones, there is another alternative for tunnel entrance lighting by means of an adequate use of shielded daytime light provided by paralumens or screens. This type of natural lighting must satisfy the same luminous levels than those of artificial lighting. Factor k values (coefficient by which luminance of the tunnel access zone must be multiplied L 20 in order to obtain luminance of the threshold zone of the tunnel L th, that is to say, L th = k L 20 ), are identical to those of the symmetrical lighting system. Likewise, the contrast development coefficient q c for natural lighting will be determined in the same way as for artificial lighting, included also, in the calculation to the interreflected light contribution Tunnel classification The parameter that allows a classification of tunnels is that of their geometric conditions and, their length, in particular. Lighting exigencies for long and short tunnels differ according to the degree in which the driver of an approaching vehicle may see through the tunnel. The capacity to see through the tunnel essentially depends on its length, but also on other design parameters (width, height, horizontal and vertical curvatures, etc.) Classification of long tunnels As far as lighting is concerned, long tunnels are classified according to traffic intensity, speed and composition, visual guidance and driving comfort Ponderation factors according to traffic intensity There is a certain ratio, but not a linear one, between traffic intensity and the risk of accidents which may be counteracted, increasing the lighting level of the tunnel to a certain extent. The second factor to bear in mind is that high speed requires better visibility and, this is the main reason why a higher luminance level on the roadway is necessary. As soon as it has been decided that a tunnel should be provided with lighting, speed has a considerable importance, due to its influence in visibility requisites. The higher the speed, the longer security distance (DS), which obliges to higher luminances in the threshold zone of the tunnel. When a tunnel is going to be illuminated, traffic intensity is defined as hourly intensity, that is to say, as the number of vehicles circulating on a road lane at a certain hour. Ponderation factors depend on traffic intensity they are detailed in Chart 3. LIGHTING ENGINEERING

229 Chapter 13. TUNNEL LIGHTING PONDERATION FACTORS ACCORDING TO TRAFFIC INTENSITY TRAFFIC INTENSITY (Vehicles/hour per lane) Unidirectional Bidirectional PONDERATION FACTOR < 60 < > > Chart Ponderation factors according to traffic composition As it has been indicated, the degree of dificulty of the task of driving a vehicle on a road is generally influenced by traffic speed and intensity, not to mention traffic composition and road layout and surrounding areas. Traffic composition also influences lighting design of tunnels in several aspects: -Percentage of lorries. - Presence/ ausence of motorbikes and/ or bicyclists. - Presence/ ausence of limitation to allow the transit of dangerous cargo. Lighting design in tunnels must be adapted to previous circumstances. Higher luminous levels or better lighting of walls or roadways is required when conditions are more difficult or more dangerous. Ponderation factors depending on traffic composition are the following: PONDERATION FACTORS ACCORDING TO TRAFFIC COMPOSITION TRAFFIC COMPOSITION Motorized traffic 0 Motorized traffic (trucks percentage > 15%) 1 Mixed traffic 2 Chart 4 PONDERATION FACTOR Ponderation factors according to visual guidance The driver of a vehicle must have adequate information to drive along the tunnel. This may be achieved dividing the longitudinal surface of the tunnel into several contrast surfaces, like for example, using a light wall and a dark ceiling. Visual guidance is of special importance: - When the user is approaching the tunnel. - Specially if the tunnel entrance contour is low. Ponderation factors according to visual guidance are the following: PONDERATION FACTORS ACCORDING TO VISUAL GUIDANCE VISUAL GUIDANCE PONDERATION FACTOR Good visual guidance 0 Poor visual guidance 2 Chart LIGHTING ENGINEERING 2002

230 Chapter 13. TUNNEL LIGHTING Visual guidance provided by tunnel lighting allows an increase in the visibility of the roadway and vertical and horizontal marking, especially the latter, installing, in turn, marking (rows of luminaires, post mounted delineators, etc.) both on the roadway and on the tunnel walls in order to improve visual guidance. In this sense, when establishing ponderation factors depending on visual guidance (Chart 5), additional installation of retroreflecting dispositives on the walls and surface of the roadway, especially for tunnels corresponding to 5, 6 and 7 lighting classes (Chart 7), will be taken into account Ponderation factors according to driving comfort Driving comfort of vehicles in tunnels must be taken into account for their lighting purposes, understood as easiness and a minimum effort on the part of users, due to complete information received and lack of complexity of the visual field. Ponderation factors according to comfort when driving are the following: PONDERATION FACTORS DEPENDING ON DRIVING COMFORT DRIVING COMFORT PONDERATION FACTOR Low comfort needed 0 Intermediate comfort needed 2 High comfort needed 4 Chart Lighting classes for long tunnels Once ponderation factors have been established according to traffic intensity and composition (Charts 3 and 4), as well as the corresponding factors depending on visual guidance and driving comfort (Charts 5 and 6), lighting classes for long tunnels are defined: LIGHTING CLASSES FOR LONG TUNNELS PONDERATION FACTOR SUM PONDERATION FACTOR Chart Lighting of long tunnels The main photometric characteristics necessary to establish lighting quality for a tunnel are the ones listed below: - Luminance level of the roadway. - Luminance level of the walls, especially up to a height of 2 m. - Luminance distribution uniformity in roadway and walls. - Limitation of glare. - Control of Flicker s effect. In Fig. 4, a cross- sectional representation of an intercity unidirectional long tunnel, is giving a detailed account of lengths and luminance LIGHTING ENGINEERING

231 Chapter 13. TUNNEL LIGHTING levels of the different zones. Nomenclature and a corresponding definition of such lighting engineering levels is established below: L 20 = Luminance in access zone. L th = Luminance in the threshold zone. L tr = Luminance in the transition zone. L n = Luminance in the interior zone. L ex = Luminance in the exit zone. Entrance Direction of traffic Exit Tunnel length Entrance Exit L20 Lth Luminance Ltr Lin Lex Access zone DS Threshold Transition zone zone DS Entrance zone Interior zone DS= Security distance Exit zone DS Direction of traffic Figure Luminance in the access zone The access zone is the part of the road in the open air, situated immediately before the entrance or tunnel portal. It covers the distance at which a driver approaching the tunnel must be able to see its interior. The length of the access zone is equal to the security distance (DS), as it has been stated in Fig. 4. The luminance value necessary at the beginning of the threshold zone must be based on the luminance value in the access zone L 20 at a separation in front of the tunnel equal to the security distance (DS). Under identical daytime light conditions, tunnels with different approximation zones and surroundings (different relief, surroundings, etc.) will have considerably different luminance values in the access zone L 20. In order to design and project the lighting installation in a tunnel, it is necessary to know the L 20 maximum value which takes place with enough frequency during the entire year, at a separation in front of the tunnel equal to the security distance (DS). As in most cases, this value L 20 depends on seasonal conditions and weather. Two simplified empirical methods for the evaluation of L 20 are used. Next, two methods to calculate luminance in the access zone are exposed. Approximation method As indicated by its name, this method only provides an approximate indication, and must only be used when there is a lack of information enough detailed about the immediate surroundings of the entrance mounth of the tunnel. This method consists in choosing the luminance of the access zone with the help of Chart 8 expressed in Kcd/m 2 (10 3 cd/m 2 ). 242 LIGHTING ENGINEERING 2002

232 Chapter 13. TUNNEL LIGHTING CHART A AVERAGE LUMINANCE OF THE ACCESS ZONE L 20 (Kcd/m2) ROAD TYPES Brightness situation in the visual field Security distance 60 m Security distance 100 to 160 m SKY PERCENTAGE (%) IN CONICAL VISUAL FIELDS AT 20 35% 25% REGULAR SNOW REGULAR SNOW 10% REGULAR SNOW B A B A B A B A B A B A 0% REGULAR SNOW B A B A (1) (1) (1) (1) (2) (3) (2) (3) (4) (4) Being: 1) Effect fundamentally depends on tunnel orientation: «B»: Low; In the north hemisphere: «southern entrance». «A»: High; In the north hemisphere: «northern entrance». For eastern and western entrances intermediate values between low and high must be chosen. 2) Effect fundamentally depends on brightness of surroundings: «B»: Low; Low reflectances of surroundings. «A»: High; High reflectances of surroundings. 3) Effect fundamentally depends on tunnel orientation: «B»: Low; In the north hemisphere: «northern entrance». «A»: High; In the north hemisphere: «southern entrance». For eastern and western entrances intermediate values between low and high must be chosen. 4) For a stopping distance of 60 m, in practice, there are no sky percentages of 35$. Notes: «northern entrance» means the entrance for drivers circulating southwards. «southern entrance» refers to the entrance for drivers circulating northwards. Chart 8 Exact method Luminance of the access zone L 20 is the average luminance contained in a conical field of vision represented by an angle of 20%, with its vertex in the position of the driver s eye. It is located at a distance before the tunnel equal to the stopping distance, and the cone oriented towards the tunnel portal on a point situated at a height of 1/4 of the tunnel mouth. Determining luminance for the access zone L 20 is extremely relevant since it predetermines the level to be obtained by means of lighting in the threshold zone. Such luminance of the access zone depends on the atmospheric conditions of the place where the tunnel is located. The calculation of the luminance of the access zone L 20 is obtained from a sketch of the surroundings of the tunnel zone. The formula below is used: L 20 = a * L c + b * L R + c * L E + d * L th where: a = % of the sky. L c = Sky luminance. b = % of the road. L R = Road luminance. c = % of the surroundings. L E = Surrounding luminance. d = % tunnel entrance. L th = Threshold zone luminance. with: a + b + c + d = 1 The unknown factor to be determined in the formula is the value of the luminance in the threshold zone (L th ). When stopping distances higher than 100 m. are faced, the mouth entrance percentage of tunnels is low (< at 10%) and since L th also has LIGHTING ENGINEERING

233 Chapter 13. TUNNEL LIGHTING a low value with respect to other luminance values, the contribution of L th may be disregarded. For a stopping distance of 60 m., the norm establishes that: L 20 = (a * L c + b * L R + c * L E ) / (1 / K) Because K never exceeds 0.1, the result is: L 20 = a * L c + b * L R + c * L E being a + b + c < 1. If the data to know exactly the value for a, b, c and d are not available, the ones defined in the following charts will be used. If surrounding values are not available, the following are used: Driving Sky Road Surroundings direction (L c ) (L R ) (L E ) Kcd/m 2 Kcd/m 2 Kcd/m 2 Rocks Edifices Snow Grass N (M, H) 2 E - O (M) 2 15 (H) S (M) 2 15 (H) Chart 9 In this chart, the value for L is known. In order to define the percentage of the sky which contributes to the value L 20 in the installation under study, Fig. 5 is used. 244 LIGHTING ENGINEERING 2002

234 Chapter 13. TUNNEL LIGHTING Security distance 160 m. Sky 35% Security distance 100 m. Sky 27% Security distance 60 m. Sky 14% Security distance 100 m. Sky 18% Security distance 160 m. Sky 14% Security distance 100 m. Sky 3% Security distance 100 m. Sky 18% Security distance 100 m. Sky 4% Figure Luminance in the entrance zone As Fig. 4 shows, tunnel entrance consists of two consecutive stretches: the threshold zone, which is the nearest to the LIGHTING ENGINEERING

235 Chapter 13. TUNNEL LIGHTING tunnel mouth and the transition zone Lighting levels for threshold zone The threshold zone is the first part of the tunnel located directly after the portal, thus, beginning at its entrance. The luminance level L th (average luminance in service of the roadway surface with maintenance of the installation), which must be provided by lighting during the day at the beginning of the threshold zone, is a percentage of the luminance of the access zone L 20 ; thus, it is verified: L th = k L 20 Factor k is established in Chart 10 taking into account the lighting system adopted (counterflux or symmetrical), security distance (DS) and lighting class defined in Chart 7, depending on ponderation factors (traffic intensity and composition, visual guidance and vehicle driving comfort). LIGHTING SYSTEM Lighting class VALUES FOR k 10 3 FOR THE THRESHOLD ZONE COUNTERFLUX Security distance (DS) 60 m 100 m 160 m SYMMETRIC Security distance (DS) 60 m 100 m 160 m Notes: For security or stopping distances (DS) ranging between ( and 160 m), values for factor (k) are obtained by linear interpolation between the figures established in the chart. Values for factor (k) for the lighting system at counterflux have been determined to guarantee, in most situations, a degree of security and comfort, at least, comparable to that achieved with the symmetric lighting system. Security or stopping distances for 60, 100 and 160 m are respectively equivalent to design speeds of the tunnel of 60, 80 and 100 km/h. Chart Threshold zone length Length of the threshold zone must be, at least, equal to the security distance (DS). For the first half of such distance (DS), luminance on the roadway will be equal to L th, that is to say, the value at the beginning of the threshold zone. Half of the security distance (DS) onwards, luminance of the roadway may gradually and linearly decrease down to a value, at the end of the threshold zone, equal to 0.4 L th (Fig. 6). The gradual reduction in the second half of the threshold zone may take place in a staged way, so that ratio between stages does not exceed the ratio 3:1 and luminance does not go under those values corresponding to linear gradual decrease Luminance of walls Wall average luminance in the threshold zone, up to a height of 2 m., must be similar to average luminance of the roadway surface Luminance and length of the transition zone The transition zone is that part of the tunnel following the threshold zone, as indicated in Fig. 4. Therefore, it begins at the end of the threshold zone and finishes at the beginning of the interior zone. 246 LIGHTING ENGINEERING 2002

236 Chapter 13. TUNNEL LIGHTING L % DS L th SCHEMATIC REPRESENTATION OF THE LIGHTING LEVEL OF DIFFERENT ZONES Ltr = Lth(1.9 + t) L tr = L th(1.9 + t) with L th = 100% and t = time in seconds Threshold zone t. sec Transition zone Security distance (DS) 100 m. 200 m. 300 m. 100 m. 200 m. 300 m. 400 m. 100 m. 200 m. 300 m. 400 m. 500 m. 100 m. 200 m. 300 m. 400 m. 500 m. 600 m. 60 Km./h 80 Km./h 100 Km./h 120 Km./h Minimum luminance in entrance zone. The 100% value corresponds to the first half of the threshold zone Figure 6 According to Fig. 6, the length of the transition zone is the distance a vehicle must travel to go from the level of luminance at the end of the threshold zone, up to the luminance value at the beginning of the interior zone, visual adaptation supposed. Consequently, for each speed of the vehicle, the allowed reduction of luminance in the transition zone L tr, depends on the distance travelled in the mentioned zone. Average luminance in service of the roadway with maintenance of the installation of the transition zone L tr decreases gradually, from the luminance of the threshold zone down to the luminance of the interior zone. In any position in the transition zone, luminance of the roadway surface must be equal or exceed luminance established in Fig. 6. The curve of Fig. 6 is the result of numerous experimental tests depending on eye adaptation, from high luminance levels to very low values which have given rise to a mathematical approximation corresponding to the following formula: L tr = L th (1.9 + t) being: t = time in seconds. In practice, a decrease in the luminance in the transition zone may take place through a series of stages which must be lower than the ratio 3:1. Luminance cannot reach values lower than those of the curve in Fig. 6. The end of the transition zone is reached when its luminance is equal to three times the level of the interior zone of the tunnel. It is compulsory that wall average luminance of the tunnel up to a 2 m. height, in any specific position of the transition zone, must not be lower than average luminance of the roadway in such a place Lighting of the interior zone The interior zone is that part of the tunnel following the transition zone directly. Its length is given by the distance existing between the end of the transition zone and the beginning of the exit zone. Luminance levels L in of the interior zone of the tunnel, constant along such a zone, since eye adaptation is finished from the high luminous values in the exterior, are LIGHTING ENGINEERING