IES TM-30-20

Accurately quantifying the color rendition characteristics of a light source is a complex problem. Color rendition affects many subjective perceptual attributes of a space, including naturalness, vividness, preference, normalness, and visual clarity. Traditionally, there have been distinct approaches for characterizing color rendition, focusing on concepts such as color fidelity, color discrimination, or color preference, and often relying on a single-number characterization. These approaches vary in their relationship to any given subjective impression. Regardless of approach, there is no one metric or measure that can accurately quantify all subjective perceptions of color rendition or identify the most desirable light source for every application. This document describes a method for evaluating light source color rendition that takes an objective and statistical approach, quantifying both overall average properties (color fidelity, gamut area) and hue-specific properties (fidelity, chroma shift, hue shift) of a light source using numerical and graphical techniques. Using various combinations of the included measures, a user is expected to be able to rely on experience and/or design guidelines to determine what is most appropriate for a specific application. This document focuses only on describing the objective characterization techniques; it does not relate values to a subjective evaluation.