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

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

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

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”

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

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

Color Discrimination 7

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

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

Spectral Power Distribution 11

Color Apearance

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

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

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

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

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)

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

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

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

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

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 = GASx100 GABB

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

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

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

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

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

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

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

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

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

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

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

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-80-08 requires 6000h CIE 1976 data 35

Check Initial and Maintained Tolerances on Color Point 36

Selecting CCT (Retail Examples) 2200K 2700K 3000K 4000K 47

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

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

Color Consistency: Getting It Right

Check Color Rendering Properties Across All 15 CIE Test Colors Ra 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

Color Rendering Guidance 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

Color Rendering Example 43

Check GAIBB A B 44

GAIBB Index Example LED A LED B 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

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.

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