Accurately quantifying the color rendition characteristics of a light source is a complex problem. Many aspects of color rendition, such as color fidelity, color discrimination, or color preference, should be simultaneously considered during the design and specification process. There is no one metric or measure that can accurately quantify all aspects of color rendition and/or identify the most desirable light source for every application.
This Technical Memorandum describes a method for evaluating light source color rendition that takes an objective and statistical approach, quantifying the fidelity (closeness to a reference) and gamut (increase or decrease in chroma) of a light source. The method also generates a color vector graphic that indicates average hue and chroma shifts, and which helps with interpreting the values of Rf and Rg.
TM-30-15 provides equations and direction for calculating Rf and Rg, including the spectral reflectance functions for the 99 CES. It is accompanied by a software tool to aid in calculation and display of the results (access information for the software tool is provided in the publication). The IES TM-30-15 color rendition method consolidates and synthesizes numerous research efforts that have been ongoing for several years, and was developed by representatives of the manufacturing, specification, and research segments of the lighting industry.
Definitions, Variables, and Procedure
Color Evaluation Samples (CES)
Range and Interpolation of Data
Calculation of Tristimulus Values
Color Space and Chromatic Adaptation Transformation
Calculation of Chromaticity Coordinates
Color Difference Formula
Fidelity Index (Rf)
Gamut Index (Rg)
Fidelity measures for specific hues angle bins and color samples
Limitations and Notes
Comparison Across CCTs
Fluorescence and Whiteness
Color Rendition Preference
Annex A - Spectral Reflectance Factors
Annex B - Color Evaluation Samples