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

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 Color science: describing Color and Color rendering
 Color science applied: getting Color right with LEDs
 Checklist when specifying LED luminaires
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 Chromaticity spaces
 Color points
 Consistency of Color points
 Color rendering
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Light
Object
Observer
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”

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

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

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Color
Discrimination

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 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

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Power as a function of wavelength

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• 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

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 Under a set of fixed viewing conditions, Colors can be matched,
quantified and compared but limitations apply
CMFs
Light spectrum
CIE XYZ
 d
After Judd and Wyszecki, 1975

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

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 Black body
 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

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+ve Duv = Color point above BBL
-ve Duv = Color point below BBL
0 Duv = Color point on BBL (only CCT sufficient)
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.

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 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

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• 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:
1. Display all Colors naturally
2. Make Colors easily distinguishable
3. Display selected vividity

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 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

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• 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
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– 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 = GASx100
GABB

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• 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
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• Halogen
• LED module Artist
• LED module Standard
• CFL
• Compact Metal Halide
• LED module Vibrant
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CRI Ra=99
R9=100
Gamut Area CRI: 99.1

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CRI Ra=77
R9=-3
GAI: 87.5

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CRI Ra=88
R9=0
GAI:113.2

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CRI Ra=98
R9=93
GAI: 100.7

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CRI Ra=83
R9=18
GAI: 96.4

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CRI Ra=84
R9=38
GAI:110.6

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CRI Ra = 96
R9= 98
GAI: 126.3

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 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

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• LEDs shift in Color with current and temperature
• Not all products behave in the same way
A, B & C product examples, operated from low to max
operating current & temperature
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LM-80-08 requires 6000h CIE 1976 data
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
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2200K 2700K 3000K 4000K
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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?
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•Phosphor on
chip LEDs
•Halogen
•CMH
•CFL
•SDW
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Color Consistency: Getting it Wrong

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Ra R1 R2 R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R13 R14 R15
LED 81 80 85 89 81 78 80 86 66 16 64 79 58 81 93 75
LED 98 98 99 98 98 98 97 98 98 96 99 98 88 98 98 98
A
A
B
B
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Ra 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

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A
B
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LED A LED B
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• ≥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
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 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