1. LEDs and Getting Color Right
Megan Carroll, LC, IESNA
Xicato Director of Sales, Northeast

2. LEDs and Getting Color Right
Color science: describing Color and Color rendering
Color science applied: getting Color right with LEDs
Checklist when specifying LED luminaires

3. Color Science: Describing Color
Chromaticity spaces
Color points
Consistency of Color points
Color rendering

4. Building Blocks of Color Perception
Observer
Light
Object
Why is Color?
-Dr. Mark Fairchild
“Our world is color coded so that all living creatures know what or whom to attract, what to eat, when to be afraid and how to behave”

5. Object properties to consider
Reflection
Transmission
Absorption
Scattering
Surface Texture
Fluorescence
Reflection
Transmission
Emission
Objects can modify incident light in various ways

6. Observer Biological factors Genetics Cognitive factors Age
Observer Metamerism
Biological factors
Genetics
Age
Cognitive factors
Color Appearance
Observer 2 no match

7. Color Discrimination 7

8. Cognitive Factors
Color is an interpretation of the stimulus we see, the biological response
Different Color appearance: ‘simultaneous contrast’
There are many other appearance phenomena, eg Chromatic Adaptation, Helmholtz-Kohlrausch Effect and Hunt Effect

9. Light: Spectral Power Distribution (SPD)
Power as a function of wavelength

10. Spectral Power Distribution11

12. Color Apearance

13. Additive Color Mixing
If Colored lights are mixed, the result will always be brighter than the individual component Colors
If the primary Colors, red, green and blue are mixed in the correct intensities, the ultimate result will be white
Yellow, magenta and cyan are called the secondary Colors
Based upon theory of additive Color mixing its possible to map every Color within the gamut defined by the primary Colors

14. Color Matching
Under a set of fixed viewing conditions, Colors can be matched, quantified and compared but limitations apply
Light spectrum
CMFs
CIE XYZ
After Judd and Wyszecki, 1975

15. CIE 1931 XY Chromaticity Diagram
2D via mathematical transform of CIE XYZ to xy (x+y+z=1)
Chroma (from a chromaticity point), hue, lightness
Color mixtures

16. Black body Black body locus (BBL) CCT
An ideal object that absorbs all electro-magnetic radiation falling on it
Its SPD, and hence color, depends only on it’s temperature
Black body locus (BBL)
It is the path that the color of an incandescent black body would take in a particular chromaticity space
CCT
The temperature in [K] that a “black body” must reach in order to produce the same color as the given source

17. Duv +Duv -Duv +ve Duv = Color point above BBL
The distance from a given Color point
to that of a blackbody radiator of the same
CCT in the 1960 uv chromaticy space is called Duv.
+ve Duv = Color point above BBL
-ve Duv = Color point below BBL
0 Duv = Color point on BBL (only CCT sufficient)

18. Color Tolerances SDCM MacAdam Ellipse
Region on the chromaticity diagram which contains all colors which are indistinguishable to the “average human eye”
SDCM
1-step : 68.26%
2-step : 95.44%
3 – step : 99.44%
MacAdam ellipses in u’v’ CIE 1976 space
SDCM: Standard Deviation of Color Matching
Δu’v’ = √(u’0–u’1)² + (v’0-v’1)²

19. Color Rendering
Color rendering is the ability of a light source to provide information on the Color of illuminated objects
To provide information on an object a light source must either:
Display all Colors naturally
Make Colors easily distinguishable
Display selected vividity

20. Color Rendering Index (CRI)
Index measures change in chromaticity of selected color patches between test source and an ideal color source for naturalness (Planckian radiator or reconstituted daylight illuminant)
Test color patches. Calculation in 1960 uv color space
R1 – R8 used to calculate CRI or Ra

21. Limitations Averaged – doesn’t tell you about specific Colors
It is a measure of naturalness based on datums from stored mental connections. Sometimes controlled vividity needed.
For the above GAI is a more appropriate metric

22. Gamut Area Index (GAI)
The area of the polygon formed by the same set of Colors in a given Color space – here 1976 u’ v’
Correlates well with increase in chroma (saturation/ vividness)
Gamut Area Index
GAI = GASx GABB

23. GAI & CRI
Position and shape of gamut area denotes where saturation occurs
Should be used with CRI: low CRI and high GAI will give overly saturated and unnatural appearance

24. Lamp Measurements Halogen LED module Artist LED module Standard CFL
Compact Metal Halide
LED module Vibrant

25. Halogen (AR 111, 60W 3000K)
CRI Ra=99
R9=100
Gamut Area CRI: 99.1

26. CFL 26W 830
CRI Ra=77
R9=-3
GAI: 87.5

27. Metal Halide 20W (3000K)
CRI Ra=88
R9=0
GAI:113.2

28. Artist LED Module CRI 98 (3000K)
CRI Ra=98
R9=93
GAI: 100.7

29. Standard LED Module CRI 83 (3000K)
CRI Ra=83
R9=18
GAI: 96.4

30. Vibrant CRI 83+ LED Module (3000K)
CRI Ra=84
R9=38
GAI:110.6

31. Vibrant CRI 90+ LED Module (3000K)
CRI Ra = 96
R9= 98
GAI: 126.3

32. Color Science Applied: Getting Color Right with LEDs
Check at what temperature module performance is quoted
Check initial and maintained tolerances on Color point
Check Color rendering properties across all 15 CIE test Colors and GAI

33. What Temperature is Module Performance Specified?
A, B & C product examples, operated from low to max operating current & temperature
LEDs shift in Color with current and temperature
Not all products behave in the same way 34

34. Check Initial and Maintained Tolerances on Color Point
White LED Supplier A CCT 3000K, Tj~112C,
test time 6000hr 1000mA
Remote Phosphor Module Supplier B CCT 3000K, Tj~117C, test time 4000hr
1000mA, 2000lm
LM requires 6000h CIE 1976 data 35

35. Check Initial and Maintained Tolerances on Color Point36

36. Selecting CCT (Retail Examples)
2200K K K K 47

37. Color Consistency Guidance
LRC (2004)
2-step MacAdam ellipse: ”…when these fixtures are used to illuminate an achromatic (white) scene. Accent lighting a white wall and lighting a white cove are some examples.”
4-step MacAdam ellipse: “…when these fixtures are used to illuminate a visually complex, multicolored scene. Lighting a display case and accent lighting multicolored objects or paintings are some examples.”
Recommended Research for 2- Step Spaces
Color consistency maintained:
1 x 2-step initial, < 3-Step maintained.
Acceptable? 38

38. Color Consistency: Getting it Wrong
Phosphor on chip LEDs
Halogen
CMH
CFL
SDW 39

39. Color Consistency: Getting It Right

40. Check Color Rendering Properties Across All 15 CIE Test ColorsRa R1 R2 R3 R4 R5 R6 R7 R8 R9
R10
R11
R12
R13
R14
R15
LED 81 80 85 89 78 86 66 16 64 79 58 93 75 98 99 97 96 88 A B A B 41

41. Color Rendering GuidanceRa
CRI
Examples
95-100
Excellent
Galleries, graphics arts industry, fashion shops, boutiques, hotels, homes
90-94
Very Good
High end shops
80-89
Good
Offices, most shops, transport hubs, leisure
70-79
Fair
Warehouses, amenity, residential outdoor
<70
Poor
Motorways, garages

42. Color Rendering Example43

43. Check GAIBB A B 44

44. GAIBB Index Example
LED A
LED B 45

45. Vivid / Natural Continuum
GAIBB and CRI Guidance
≥110 GAIBB and look at area shape/position in Color space
≥80 CRI
Sometimes a need for vivid blues, whites, and reds, without excessive enhancement
Balance (higher CCT has a higher GAI)
Vividness
Applications: Retail: fashion, toys, cars. Galleries: some contemporary art
Application need: bold and distinct target colors, crisp whites
Naturalness
Applications: retail: fresh foods, general department stores
Application need: flowing, natural, balanced colors. Harmony is better than divergence
Vivid / Natural Continuum
Mix in an installation, e.g. for general and accent 58

46. Color Related Checklist When Specifying LED Luminaires
LED source LM-80 report for the same drive current and case temperature (or higher) used in the luminaire.
Some reports may be at a relatively low case temperature (TC) such as 55˚C, while in the luminaire it may be operating at 85˚C.
Color consistency (initial and maintained) specification, supporting reliability data, and warranty.
Make sure the Color consistency specification is suitable for the application.
Color rendering properties across all 15 CIE test Colors, including saturated ones. For some applications check gamut area or GAI.
Having CRI alone (Ra) will only communicate the ability to render 8 CIE pastel Colors).
Working production sample of the module in the luminaire that corresponds to the LM-79/LM-80 report.
This ultimately is the route to qualitative and quantitative performance.

47. LEDs and Getting Color Right
Megan Carroll, LC, IESNA
Xicato Director of Sales, Northeast