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Kleuraspecten van LED toestellen - KAHO / Laboratorium voor Lichttechnologie
1. Kleuraspecten van
LED toestellen
Richard Vanraes
Peter Hanselaer
Laboratorium voor Lichttechnologie, Gent
KAHO Sint-Lieven
KU Leuven
2. Outline
• Light&Lighting Laboratory
• Colorimetry in a nutshell
• Colorimetry of LEDs
• RGB or phosphor white?
• Impact of junction temperature?
• Impact of viewing angle?
• Impact of operating time?
• What about colour rendering ?
2
9. Colorimetry in a nutshell:
colour classification
Munsell
Hue 5Y 5Y 8/12
9
10. Colorimetry in a nutshell:
colour matching
Three primary sources
Test colour K K AA BB CC
with luminance LK LK A.LA B.LB C.LC
10
11. Colorimetry in a nutshell:
trichromatic values
Primaries
Trichromatic values x 0.706 x 0.863 x 0.863
Kleurcomponenten
X,Y,Z
11
12. Colorimetry in a nutshell:
colour coordinates
Ignoring brightness, only two numbers are
needed: colour coordinates (x,y)
(Kleurcoördinaten)
X
x
X Y Z
Y
y
X Y Z
12
13. Characteristics Colorimetry in a nutshell:
chromaticity diagram
• Spectrum locus
• Additive mixing
• Purity, saturation
• Colour gamut
• Primary colours
13
14. Colorimetry in a nutshell:
correlated colour temperature
The correlated colour temperature is the
temperature of a Planckian radiator having
the chromaticity nearest the chromaticity
associated with the given spectral distribution
on a diagram where the (CIE1931 standard
observer based) u, v coordinates of the
Planckian locus and the test stimulus are
depicted.
14
15. Colorimetry in a nutshell:
correlated colour temperature
Black Body Locus
EN 12464
• CCT<3300 K :
“warm white”
• 3300 K< CCT< 5300 K:
“neutral white”
• CCT>5300K:
“cool daylight”
15
16. Colorimetry in a nutshell:
colour rendering
The colour rendering index CRI of a light
source is a measure of the shift in
chromaticity of a set of objects when
they are lighted by the source as
compared to be lighted by a reference
source of comparable colour
temperature.
16
17. Colorimetry in a nutshell:
colour rendering
Testsamples (8 of 14) Testlamp
Colour coordinates
<colour differences>
Standardlamp
Colour coordinates
17
18. Colorimetry in a nutshell:
chromatic adaptation
• The visual system is able to partially or
completely disaccount for the colour of the
illuminant such that the white of the illuminant
is always perceived as “white” (complete
adaptation)
• This is accomplished by changing the
sensitivities of the red, green and blue visual
channel.
18
26. RGB or Phosphor White?
Experiment
LEDs from 3 manufacturers
• 1 phosphor-white package (350 mA)
• 1 red-green-blue package
Comparison of consumed power for same
• luminous flux
• colour coordinates
• heat sink
with PW as reference
26
27. RGB or Phosphor White?
Results
P (W) eff. (lm/W) P (W) eff. (lm/W)
MFR flux (lm) CIE (x,y)
PW PW RGB RGB
M1 84.1 (0.31, 0.33) 1.16 72.5 2.44 34.5
M2 45.9 (0.32, 0.33) 1.06 43.3 2.50 18.4
M3 77.6 (0.30, 0.32) 1.11 69.9 2.61 29.7
1,8
1,6
1,4
PW
1,2
R
P (W)
1
0,8 G
0,6
B
0,4
0,2
0
M1
Cree M2
Lumileds M3
SSC
27
28. Impact of junction temperature?
Spectrum
E
1240
Band gap Eg (nm)
Eg (eV )
Decrease of the bandgap: increase of wavelength
Decrease of recombination rate: decrease of flux
28
33. Impact of junction temperature
Self heating
With and without heat sink
Different ambient temperature
Luminous flux is dependent on
heat sink, position of heat sink, . . .
33
35. Impact of viewing angle?
Spectrum
Negligible impact when using
remote phosphor LEDs
35
36. Impact of operating time?
Chromaticity
Degradation of
Experiments the phosphor
36
37. Impact of operating time?
CCT and CRI
CRI Verschil in %
CCT [K] Verschil in %
September Januari April Januari tov April tov
September Januari April Januari tov April tov
2010 2011 2011 september september
2010 2011 2011 september september
Lamp 1 90 89 89 -1% -1%
Lamp 1 4186 4066 4075 -3% -3%
6876 6637 6818 -3% -1% Lamp 2 72 73 73 1% 1%
Lamp 2
Lamp 3 3709 3653 3701 -2% 0% Lamp 3 76 78 80 3% 5%
4016 3874 3834 -4% -5% Lamp 4 69 70 69 1% 0%
Lamp 4
Lamp 5 4207 4077 4128 -3% -2% Lamp 5 76 78 79 3% 4%
Lamp 6 3194 3167 3194 -1% 0% Lamp 6 65 66 65 1% 1%
Lamp 7 3307 3153 3175 -5% -4% Lamp 7 71 71 71 0% 0%
Lamp 8 3853 3717 3743 -4% -3% Lamp 8 77 77 77 0% 0%
Lamp 9 3365 3307 3326 -2% -1% Lamp 9 88 88 88 0% 0%
Lamp 10 3678 3470 3670 -6% 0% Lamp 10 78 77 80 -1% 3%
Lamp 11 4733 4586 4625 -3% -2% Lamp 11 65 65 65 0% 0%
Lamp 12 5329 5037 5104 -5% -4% Lamp 12 73 72 73 -1% 0%
gemiddelde 75 76 76 0% 1%
mediaan 76 77 77 1% 1%
IEC PAS 62717:
CRI after 6000 h: maximum -5
CCT after 6000 h: within 1 class (100 K)
37
38. What about colour rendering?
Problem
Reference Illuminant Ra=83
Ra=70
Ra=60
Ra=100
Ra=85
Ra=50
Large colour differences towards reference
low quality !
Kevin.Smet@kahosl.be
38
38
39. What about colour rendering?
Memory colours
The more similar a light source renders the familiar
object colours to their memory colours,
the better the colour quality.
39
40. What about colour rendering?
Determination of Memory colours
Colour appearance rating of real familiar objects
The closer the test illuminant reaches the memory
colour of 10 objects, the higher the MCRI
40
Kevin.Smet@kahosl.be 40
41. What about colour rendering?
Experimental validation
• Aspects of colour quality investigated
– Preference/attractiveness (appreciation)
– Naturalness
• Thirteen colour quality metrics (CIE TC 1-69)
• Combining results of 9 psychophysical studies
Correlation between 13 metric predictions and
all the visual data is calculated.
41
Kevin.Smet@kahosl.be 41
42. What about colour rendering?
Experimental validation
Memory metric for preference/attractiveness: ravg = 0.88
GAI_Ra for naturalness: ravg = 0.85
42
Kevin.Smet@kahosl.be 42
43. What about colour rendering?
Optimizing LED clusters
Xb Xg Xr Xw X
Yb Yg Yr Yw Y
Zb Zg Zr Zw Z
xi
Xi .Yi
yi
zi
Zi .Yi
yi
Optimum MCRI
ánd efficacy
43
Kevin.Smet@kahosl.be 43
44. What about colour rendering?
Visual performance
Visual experiment with 2700K setting:
MEAN/MEDIAN Attractiveness Preference Naturalness Vividness Memory
Sa optimized LED 7.8 / 8.0 7.9 / 8.0 7.2 /8.0 7.4 /8.0 7.9 /8.0
RGB LED cluster 6.0 / 6.0 5.6 / 6.0 4.2 / 4.5 6.3 / 7.0 4.8 / 5.0
Incandescent lamp 5.8 / 6.0 6.0 / 6.0 6.9 / 7.0 6.2 / 6.5 6.5 / 6.0
• Sa optimized LED lamp scored significantly better (p<0.05)
than the incandescent source for attractiveness, preference and
memory.
• No significant differences for naturalness and vividness !
44
Kevin.Smet@kahosl.be 44