Lighting fundamentals
About light and photometrics Generation of light Human vision Black body Colour Basic principles of lighting Light sources
Light Vision Colour
What is light? Light is electromagnetic radiation and The human eye is sensible to this radiation
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
The spectrum of the electromagnetic radiation
Visible radiation and neighbours
The spectrum of light
Human vision
The human field of view
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)
Photoreceptors
The visual system
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 )
Distribution of cones and rods
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
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
3 types of cones Each one sensitive to 1 of the 3 basic colours: Red, Green, Blue
Colour recognition
Photopic and scotopic vision
Photopic vision
Scotopic vision
Mesopic vision
Colours in the visible spectrum
The colour chart of CIE (Commission Internationale de l Eclairage)
Measurement of colours
The colour of some light sources
The limits of visible radiation Ultraviolet (UV) Visible light Infrared (IR)
Ultraviolet
Infrared
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)
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
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
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 (6,626 10-34 J s) c Speed of light (2,99792 108 m/s) k Boltzman s constant (1,38 10-23 J/K) λ Wavelength (m) t Temperature of black body (Κ)
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
The displacement of the peak wavelength
Some visible black body radiations
Black body fits the spectrum of incandescent lamps
. and solar irradiance too
Solar light, in and out the atmosphere Photometry Lab
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
Colour temperature of various light sources
Light colour of 3 fluorescent lamps
Colour temperature vs. black body temperature Low colour temperature ( cold black body) indicates warm light colour Confusion!
Warm and cool sky
A cold and a warm fluorescent lamp Cold 6.500K Warm 3.000K
Identification of colour temperature on the label of a lamp 2.700Κ 6.500Κ
Influence of light colour on human beings
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.
Determination of CRI/Ra Colour targets Spectra of targets Spectra of targets
An example: Measurement of CRI/Ra of some LED lamps
Light of 3 lamps T= 4200K Ra=90 T= 1800K Ra=8 T= 6400K Ra=20
Colour rendering groups
Identification of CRI (or Ra) and colour temperature on lamps
An example
Photometrics
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
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
Determination of luminous flux Radiation P(λ) Eye sensitivity V(λ) Luminous flux
Luminous flux of typical lamps
Lamp efficacy: Produced lumens per Watt of consumed power
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
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
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
Plane and solid andles Plane angle Solid angle The solid angle Ω is produced by rotating the plane angle γ
Solid angles of some objects
Luminous intensity Luminous intensity I is the amount of luminous flux dφ (lumens) per unit solid angles dω (steradians) I d d
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
Luminous intensity of some typical light sources
The principle Distribution of luminous intensity Polar diagram Cartesian diagram
Polar distributions
CIE* C-planes * Commission Internationale de l Eclairage
CIE C-planes C 270 C 180 C 0 C 180 C 0 C 90 C 270 C 90
Some examples
Definition of illuminance Illuminance is the luminous flux density on the illuminated surface Unit: lux (lx) d E da 1lumen 1lux 2 1m
Some typical illuminances
Illuminance requirements according to the European Norm ΕΝ 12464-1
Illuminance range of human vision
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
Illuminance meters(luxmeters) Portable General use More accurate with mili Lux resolution Benchtop for laboratories
A benchtop luxmeter of high accuracy
Isolux diagrams
10 8 6 4 2 0-2 -4 X(m ) Pseudo-colour Isolux diagram of road illumination 8 12 16 10 14 18 A A A 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 Y(m)
An example from a lighting design
Another example of indoor illumination
Pseudo-colours correspond to illuminance values
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
Luminance of some light sources Luminances in candela/m 2 (cd/m 2 )
Luminance meters Simple portable Spot luminance meter with viewfinder Luminance camera
Illuminance is proportional to the inverse of the distance squared E2 E 1 d d 2 1 2 2
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
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
The cone diagram Height of luminaire from illuminated surface Beam diameter Average illuminance
The beam angle Beam angle: The angle at which the lighting intensity takes 50% of the maximum intensity
Cone diagram of a narrow beam spot luminaire
Cone diagram of a wide beam spot luminaire
Cone diagram of a LED spot
Cone diagram of a fluorescent tube luminaire
Glare The Söllner diagram
Explanation of Söllner diagram
Glare category classes of Söllner diagram
Παράδειγμα χρησιμοποίησης διαγράμματος Söllner
Unified Glare Rating (UGR) Combined glare from all luminaires in our visual field
UGR calculation
Maximum allowed values of UGR according to the European Norm ΕΝ 12464-1
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
Reduction of glare A luminaire with high UGR i.e. with high glare A luminaire with low UGR i.e. with low glare
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
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
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
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
Συντελεστής χρησιμοποίησης (παράδειγμα) Indoor luminaire Length: 15 m Width: 5 m Height: 3 m Thus: LW K h ( L W ) K m 15 5 3 (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 0.80 0.80 0.80 0.70 0.70 0.70 0.50 0.50 0.50 0.80 0.80 0.80 0.70 0.70 0.70 0.50 0.50 0.50 ρ-walls 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 0.70 0.50 0.30 ρ-working 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 plane 0.60 0.31 0.24 0.20 0.30 0.24 0.20 0.29 0.23 0.20 0.30 0.23 0.20 0.29 0.23 0.20 0.28 0.23 0.20 0.80 0.36 0.29 0.25 0.35 0.29 0.25 0.33 0.28 0.24 0.34 0.28 0.24 0.34 0.28 0.24 0.33 0.28 0.24 1.00 0.40 0.34 0.29 0.39 0.33 0.29 0.37 0.32 0.28 0.38 0.32 0.29 0.38 0.32 0.28 0.36 0.31 0.28 1.25 0.43 0.38 0.33 0.42 0.37 0.33 0.40 0.36 0.32 0.42 0.36 0.33 0.41 0.36 0.32 0.40 0.35 0.32 Room 1.50 0.46 0.40 0.37 0.44 0.40 0.36 0.42 0.38 0.35 0.45 0.39 0.36 0.44 0.39 0.35 0.42 0.38 0.35 index 2.00 0.49 0.45 0.41 0.48 0.44 0.41 0.46 0.42 0.40 0.48 0.44 0.41 0.47 0.43 0.40 0.45 0.42 0.39 K 2.50 0.51 0.47 0.44 0.50 0.46 0.44 0.47 0.45 0.42 0.50 0.46 0.43 0.49 0.46 0.43 0.47 0.44 0.42 3.00 0.53 0.49 0.46 0.51 0.48 0.46 0.49 0.46 0.44 0.52 0.48 0.46 0.51 0.48 0.45 0.49 0.46 0.44 4.00 0.54 0.52 0.49 0.53 0.51 0.49 0.51 0.49 0.47 0.54 0.51 0.49 0.53 0.50 0.48 0.50 0.48 0.46 5.00 0.55 0.53 0.51 0.54 0.52 0.50 0.52 0.50 0.49 0.55 0.53 0.51 0.54 0.52 0.50 0.51 0.50 0.48
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
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
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
First we determine how clean is the room
The depreciation factors depend on the maintenance interval Luminaire maintenance factor (LMF) Lamp lumen maintenance factor (LLMF) Lamp survival factor (LSF)
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 0.80 0.70 0.50
Flux Code / Luminaire classification CIE, CEN, DIN, UTE, BZ flux codes How can we decode them?
CIE Flux Code N 100 / 2 1 2 Examples: CIE 30 40 50 100 65, CIE 48 78 95 99 70 N 100 2 2 N 100 3 / 2 3 2 N 4 N 5 100 2 100 2 4 lum 100 lum lamp N LOR 5
An example of the CIE Flux Code of a luminaire CIE 48 78 95 99 70 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%
Ingress Protection (IP) rating
Examples of IP of luminaires IP 20 IP 44 IP 65 IP 67
IP Ingress protection rating IK Shock protection rating
to be continued Light sources