Lighting fundamentals

Transcription

1 Lighting fundamentals

2 About light and photometrics Generation of light Human vision Black body Colour Basic principles of lighting Light sources

3 Light Vision Colour

4 What is light? Light is electromagnetic radiation and The human eye is sensible to this radiation

5 Light generation E E E2 E1 h f f h E2 = energy associated with the excited orbit E1 = energy associated with the normal orbit h = Planck's constant f = frequency of the emitted radiation as the electron moves from level 2 to level 1 n v f λ=wavelength of radiation n=index of refraction of the medium

6 The spectrum of the electromagnetic radiation

7 Visible radiation and neighbours

8 The spectrum of light

9 Human vision

10 The human field of view

11 How light excites the eye? Through sensors in the retina Two types of sensors: Cones (6-7 millions per eye) Rods (around 120 millions per eye)

12 Photoreceptors

13 The visual system

14 Location of cones and rods Cones: Mainly around the central area of the retina (fovea) Rods: Towards the periphery of the retina (max at ±20 o )

15 Distribution of cones and rods

16 Cones Axial vision (±5 o =10 o visual field) Less sensitive than rods Their sensitivity decreases at low light levels Photopic vision (daylight, illuminated areas) Responsible for colour recognition Highest sensitivity at 555 nm

17 Rods Peripheral vision & motion detection 1000 times more sensitive than cones They function under low light levels (dark adapted) Scotopic vision (night vision) No colour recognition (at night we see in shades of grey!) Highest sensitivity at 507 nm

18 3 types of cones Each one sensitive to 1 of the 3 basic colours: Red, Green, Blue

19 Colour recognition

20 Photopic and scotopic vision

21 Photopic vision

22 Scotopic vision

23 Mesopic vision

24 Colours in the visible spectrum

25 The colour chart of CIE (Commission Internationale de l Eclairage)

26 Measurement of colours

27 The colour of some light sources

28 The limits of visible radiation Ultraviolet (UV) Visible light Infrared (IR)

29 Ultraviolet

30 Infrared

31 Colour of light sources How do we measure the colour of light sources? Comparing the colour of the light of the source with the colour of the radiation of a black body (Planckian radiator, black body of Max Planck)

32 The black body Theoretical Definitely not only black in colour A black painted body absorbs only the visible light (but not UV, IR, X-rays etc) The black body (Planckian radiator) absorbs ALL radiations

33 How the black body works? It is characterized by 2 physical quantities: Temperature and wavelength of radiation It absorbs an external radiation (any radiation). This increases its temperature External radiation Absorption Temperature rise It radiates. The wavelength of its radiation depends on its temperature Black body radiation ~ Black body temperature

34 Black body radiation, Law of Max Planck, Nobel award 1918 P λ Watts of black body radiation/m 2 of black body surface/m of wavelength h Planck s constant (6, J s) c Speed of light (2, m/s) k Boltzman s constant (1, J/K) λ Wavelength (m) t Temperature of black body (Κ)

35 Wien s law of displacement λ max Temperature=Constant If the temperature of the black body rises, then the peak of the spectrum moves towards the lower wavelengths

36 The displacement of the peak wavelength

37 Some visible black body radiations

38 Black body fits the spectrum of incandescent lamps

39 . and solar irradiance too

40 Solar light, in and out the atmosphere Photometry Lab

41 Colour temperature Colour temperature is a measure for describing the colour of light sources It indicates the equivalent temperature that a black body would need to have in order to produce light of the same colour Thus, we express the colour of a light source with the temperature (in Kelvins) of the respective black body

42 Colour temperature of various light sources

43 Light colour of 3 fluorescent lamps

44 Colour temperature vs. black body temperature Low colour temperature ( cold black body) indicates warm light colour Confusion!

45 Warm and cool sky

46 A cold and a warm fluorescent lamp Cold 6.500K Warm 3.000K

47 Identification of colour temperature on the label of a lamp 2.700Κ 6.500Κ

48 Influence of light colour on human beings

49 Definition of colour quality The colour quality of a light source is expressed by a value between 0 and 100 known as Colour Rendering Index (CRI) or Ra Test strips are illuminated from the light source and the reflected light is measured. CRI is the effective sum of the reflected light.

50 Determination of CRI/Ra Colour targets Spectra of targets Spectra of targets

51 An example: Measurement of CRI/Ra of some LED lamps

52 Light of 3 lamps T= 4200K Ra=90 T= 1800K Ra=8 T= 6400K Ra=20

53 Colour rendering groups

54 Identification of CRI (or Ra) and colour temperature on lamps

55 An example

56 Photometrics

57 What is light? Light is a radiation that is detected by the eye Therefore, the generation of light depends on: the power P(λ) of the radiation and the spectral sensitivity V(λ) of the eye 780nm 380nm P( ) V ( ) d

58 Luminous flux The measure of the quantity of light is called luminous flux and is defined as: K m 780nm 380nm P( ) V ( ) d Φ is measured in lumen (abbreviation: lm) P(λ) in Watt K m =683lumen/Watt

59 Determination of luminous flux Radiation P(λ) Eye sensitivity V(λ) Luminous flux

60 Luminous flux of typical lamps

61 Lamp efficacy: Produced lumens per Watt of consumed power

62 How do we measure light? The light source is treated as a point Let s imagine that point source emitting light to all directions The light to each direction is emitted from the point source in a virtual cone This cone is called solid angle

63 Solid angle The light from the point- source is emitted in solid angles Solid angle is the 3-dimensional equivalent of a 2-dimensional angle

64 Definition of solid angle Given a sphere of radius r, a cone that subtends an area A encloses a solid angle Ω Unit: Steradian Abbreviation: sr

65 Plane and solid andles Plane angle Solid angle The solid angle Ω is produced by rotating the plane angle γ

66 Solid angles of some objects

67 Luminous intensity Luminous intensity I is the amount of luminous flux dφ (lumens) per unit solid angles dω (steradians) I d d

68 Definition of luminous intensity Luminous intensity describes the power of the light source to emit light in a given direction It is the fraction of the luminous flux of the source that is emitted into a certain direction, into a certain solid angle I d d 1lumen 1candela 1steradian

69 Luminous intensity of some typical light sources

70 The principle Distribution of luminous intensity Polar diagram Cartesian diagram

71 Polar distributions

72 CIE* C-planes * Commission Internationale de l Eclairage

73 CIE C-planes C 270 C 180 C 0 C 180 C 0 C 90 C 270 C 90

74 Some examples

75 Definition of illuminance Illuminance is the luminous flux density on the illuminated surface Unit: lux (lx) d E da 1lumen 1lux 2 1m

76 Some typical illuminances

77 Illuminance requirements according to the European Norm ΕΝ

78 Illuminance range of human vision

79 The acuity of vision is not increased after a certain illuminance level For common duties our visual perception is not improved at more than 3000 lux

80 Illuminance meters(luxmeters) Portable General use More accurate with mili Lux resolution Benchtop for laboratories

81 A benchtop luxmeter of high accuracy

82 Isolux diagrams

83 X(m ) Pseudo-colour Isolux diagram of road illumination A A A Y(m)

84 An example from a lighting design

85 Another example of indoor illumination

86 Pseudo-colours correspond to illuminance values

87 Luminance Luminance L is defined as the luminous intensity I in a specific direction of a light source or of a surface that reflects light, divided by the projected area A as viewed from that direction Unit: candela/m 2 (cd/m 2 ) L I A

88 Luminance of some light sources Luminances in candela/m 2 (cd/m 2 )

89 Luminance meters Simple portable Spot luminance meter with viewfinder Luminance camera

90 Illuminance is proportional to the inverse of the distance squared E2 E 1 d d

91 Illuminance is proportional to the cosine of the angle of incidence E E cos 2 1 The same flux is spread over a larger area

92 The cosine law E 1 d I 2 Vertical radiation E 2 : Light falls obliquely E 2 E1 cos Cosine law I E cos 2 d 2

93 The cone diagram Height of luminaire from illuminated surface Beam diameter Average illuminance

94 The beam angle Beam angle: The angle at which the lighting intensity takes 50% of the maximum intensity

95 Cone diagram of a narrow beam spot luminaire

96 Cone diagram of a wide beam spot luminaire

97 Cone diagram of a LED spot

98 Cone diagram of a fluorescent tube luminaire

99 Glare The Söllner diagram

100 Explanation of Söllner diagram

101 Glare category classes of Söllner diagram

102 Παράδειγμα χρησιμοποίησης διαγράμματος Söllner

103 Unified Glare Rating (UGR) Combined glare from all luminaires in our visual field

104 UGR calculation

105 Maximum allowed values of UGR according to the European Norm ΕΝ

106 A typcial UGR table of a luminaire ρ: Reflectance of ceiling, walls, floor X, Y: Length and Width of room H: Height of luminaire from working plane S: Spacing between luminaires

107 Reduction of glare A luminaire with high UGR i.e. with high glare A luminaire with low UGR i.e. with low glare

108 LOR Light Output Ratio (LOR) Lumin ous flux emitted by the lu min aire Lumin ous flux produced by the lamps LOR=0.67 means that the emitted flux is 67% of the produced

109 Utilization factor (UF or CU) The percentage of the luminous flux of the lamps that falls on the working plane i.e the useful luminous flux Lumin ous flux on the working plane UF Lumin ous flux produced by the lamps In Europe: Utilization Factor (UF) In USA: Coefficient of Utilization (CU) Example UF=0.68 The luminous flux falling on the working plane is 68% of the total luminous flux of the luminaire lamps

110 Utilization Factor depends on: the room dimensions the reflectance of the room surfaces the height of luminaires from the working plane the spacing between luminaires

111 The influence of the dimensions of the room is integrated in one size: the room index Κ LW K h ( L W ) m Working plane

112 Συντελεστής χρησιμοποίησης (παράδειγμα) Indoor luminaire Length: 15 m Width: 5 m Height: 3 m Thus: LW K h ( L W ) K m (15 5) K 1.25 Utilization factors Nominal spacing-to-height ratio (SHRNOM) = 1 Reflectance Suspension ratio J=0 Suspension ratio J=1/4 ρ-ceiling ρ-walls ρ-working plane Room index K

113 The Maintenance Factor (MF) The lighting installation is depreciated over the time (ageing of lamps, depreciation of optical materials, dirt over the reflecting surfaces etc) The lighting designer estimates that depreciation quantitevely (MF) and increases respectively the initial lighting level Over the time, that lighting level will be decreased due to the ageing and the dirt. Thus, the initially high lighting level will be decreased, over the time, to a level not lower than the required. 113

114 An example Required illuminance revel: 500 lux Estimated depreciation: 20% Maintenance factor (MF): 0.80 (80%) Initial illuminance level: 500/0.80=625 lux The initial 625 lux will be gradually decreased due to the ageing and the accumulation of dirt to: 625X0.80=500 lux i.e. at the required level 114

115 MF sums the depreciation of the lighting system due to the factors: Lamp lumen maintenance factor (LLMF) Lamp survival factor (LSF) Luminaire maintenance factor (LMF) Room surface maintenance factor (RSMF) MF = LLMF Χ LSF Χ LMF Χ RSMF

116 First we determine how clean is the room

117 The depreciation factors depend on the maintenance interval Luminaire maintenance factor (LMF) Lamp lumen maintenance factor (LLMF) Lamp survival factor (LSF)

118 A fast method to determine MF Description of the room & equipment Maintenance factor Very clean room, cleaning of luminaires once per year, burning of lamps 2000 hours/year, type of luminaires of direct lighting with protection from the accumulation of dust Typically clean room, cleaning of luminaires once per 3 years, burning of lamps 2000 hours/year, type of luminaires of direct/indirect lighting without protection from the accumulation of dust Room with pollution, cleaning of luminaires once per 3 years, burning of lamps 8000 hours/year, grouped replacement of lamps every 8000 hours, luminaires without protection from the accumulation of dust

119 Flux Code / Luminaire classification CIE, CEN, DIN, UTE, BZ flux codes How can we decode them?

120 CIE Flux Code N 100 / Examples: CIE , CIE N N / N 4 N lum 100 lum lamp N LOR 5

121 An example of the CIE Flux Code of a luminaire CIE Φ π/2 =0,48 Φ 2π : 48% of the downward flux is emitted in the solid angle Ω=π/2 Φ π =0,78 Φ 2π : 78% of the downward flux is emitted in the solid angle Ω=π Φ 3π/2 =0,95 Φ 2π : 95% of the downward flux is emitted in the solid angle Ω=2π/3 Φ 2π =0,99 Φ lum : 99% of the total flux of the luminaire is emitted downwards. Thus only 1% of the total flux of the luminaire is emitted upwards. Φ lum =0,70 Φ lamp : The luminaire emits in the room 70% of the total flux of the lamps. Thus LOR = 70%

122 Ingress Protection (IP) rating

123 Examples of IP of luminaires IP 20 IP 44 IP 65 IP 67

124 IP Ingress protection rating IK Shock protection rating

125 to be continued Light sources