categorical color rendeing of led light sources h. yaguchi, n. endoh, t. moriyama and s. shioiri cie...
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CATEGORICAL COLOR RENDEING OF LED LIGHT
SOURCES
H. Yaguchi, N. Endoh, T. Moriyama and S. Shioiri
CIE Expert Symposium on LED Light SourcesJune 7, 2004, Tokyo
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INTRRODUCTION
• Energy efficiency and color rendering– CIE CRI is based on color difference
• Importance of color name– To communicate color information in every day life.
– To categorize objects and recognize them.– Color name does not depend on viewing condition.
• Color rendering based on color categorization
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PURPOSE
• To evaluate color rendering of LED light sources to take account of color categorization.
• The Subjective method by categorical color naming experiment.
• The Objective methods using the CIE color rendering index and the categorical color rendering index.
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EXPERIMENT
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Color samples
• 292 Munsell color chips• V: 2, 4, 6, 8• C: 0, 2, 4, 6,• • •• H: 5R, 10R, 5YR, 10YR, 5R,• • •
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Spectral power distributions of light
sources
00.20.40.60.81
300400500600700800wavelengthÅinmÅjrelative spectral irradiance
D65LED(7500K)LED(5100K)LED(4000K)LED(2800K)
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Categorical Color Naming
• Sort samples into 11 basic color categories: – red (aka), gree (midori), yellow (ki), blue (ao), orange (daidai), pink (momo), purple (murasaki), brown (cha), white (shiro), gray (hai), and black (kuro).
• Sorting was repeated three times.• Select samples sorted into the same category for all three trials.
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Subjects
• 9 subjects• Age from 21 to 55• Normal color vision checked by the ND-100 hue test.
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Color samples in the Munsell hue circle, named
consistently
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R
P Y
B G
R
P Y
B G
R
P Y
B G
R
P Y
B G
R
P Y
B G
Result
Observer Kn, v=6
LED(7500K) (5100K) (4000K) (2800K)
D65
• Munsell color circles
Same color samplesare named different color
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Percent Correct
• ND65: number of samples sorted into a color category consistently for three trials under the D65 simulator.
• Ns: number of samples, under test light source, sorted into the same color category as in the case of the D65 simulator.
• Nd: number of samples, under test light source, sorted into the different color category from the case of the D65 simulator.
• Percent correct = 100(Ns - Nd)/ ND65
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Percent Correct for 8 color names
0
20
40
60
80
100
Red PinkOrangeYellowGreenBlue
PurpleBrown
Color Name
Percentage of correct (%) LED7500K
LED5100K
LED4000K
LED2800K
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CIE color appearance model (CIECAM97s)
CIECAM97sINPUTLuminance of adapting fieldTristimulus values of sampleTristimulus values of whiteParameters for viewing conditionLAX, Y, ZXw, Yw, ZwOUTPUTHue, hLightness, JBrightness, QSaturation, sChroma, CColorfulness, M
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Color map in CIECAM97s75<J 55<J<75
35<J<55 J<35
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How to calculate
●CCRI for each test sample
● Averaged CCRI
CCRIi=100•Si∩ StSt
CCRI=( CCRIi)i=1
8
∑ /8
Categorical color rendering index (CCRI)
×
×
×
×
Boundary of color samples under the test light source “St”
Boundary of color samples under D65
×
×
×
× Cmax
Hmin
Hmax
Cmin
Chroma
Hu
e an
gle
Boundary of Color name “Si”
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CCRI of 5 light sources
0
20
40
60
80
100
120
Red Pink Orange Yellow Green Blue Purple
Color name (i)
CCRIi
D65 Simulator
LED7500
LED5100
LED4000
LED2800
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Ri, CCRIi and percent correctD65 LED75 LED510 LED40 LED28
redR9 83 52 -1 14 -5
CCRIred 97 88 90 91 83
PCred 100 73 83 73 63
yellow
R10 90 94 74 94 91
CCRIyellow 90 100 100 82 78
PCyellow 100 83 85 78 80
greenR11 95 68 63 64 52
CCRIgreen 95 85 91 88 85
PCgreen 100 82 91 81 78
blueR12 92 56 53 61 72
CCRIblue 97 100 100 100 98
PCblue 100 93 89 86 81
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Correlation among Ri, CCRIi and PC
Red
-20
0
20
40
60
80
100
LED75 LED51 LED40 LED28
Light sources
Color rendering index
R9
CCRIred
PCred
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Correlation among Ri, CCRIi and PCYellow
0
20
40
60
80
100
120
LED75 LED51 LED40 LED28
Light sources
Color rendering index
R10
CCRIyellow
PCyellow
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Correlation among Ri, CCRIi and PC
Green
0
20
40
60
80
100
LED75 LED51 LED40 LED28
Light sources
Color rendering index
R11
CCRIgreen
PCgreen
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Correlation among Ri, CCRIi and PC
Blue
0
20
40
60
80
100
120
LED75 LED51 LED40 LED28
Light sources
Color rendering index
R12
CCRIblue
PCblue
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Ra, CCRIa and percent correct
Light sources
D65 LED75 LED51 LED40 LED28
Tcp(K) 6420 7500 5100 4000 2800
Ra 96 84 79 80 75
CCRIa 95 95 95 91 87
PCa 100 80 82 77 74
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Correlation among Ra, CCRIa and PC
Average
0
20
40
60
80
100
LED75 LED51 LED40 LED28
Light sources
Color rendering index
Ra
CCRIa
PCa
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SUMMARIES
• Color rendering qualities of white LED (blue LED and yellow phosphor type) light sources of four different Tcp were examined with PC, Ri, and CCRIi.
• Correlation between CCRI and PC for different color temperature light sources is higher than those between CIE CRI and PC.
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CONCLUSION
• If you like to take account of color categorization in order to evaluate practical color rendering quality of white LED light sources, the CCRI can be recommended rather than Ra.