Color rendering index

The color rendering index (CRI) measures how accurately a light source reveals object colors compared with a reference source of similar correlated color temperature.

CIE 13.3: The CIE method that specifies how to calculate the general color rendering index and special indices. It defines the standard calculation behind the familiar CRI value.
TM-30: An IES method for evaluating light-source color rendition using a larger sample set and measures of fidelity and gamut. It addresses CRI’s limited sample set and inability to describe gamut shifts.
Light-emitting diode: A semiconductor device that emits light when electric current passes through it. LED spectra vary widely, so CRI helps compare their color rendition.
Color appearance: The perceived hue, lightness, and chroma of an object under particular viewing conditions. CRI compresses a complex aspect of color appearance into a summary score.
Test color samples: A set of standardized color samples used to evaluate color rendering under an illuminant. Their measured color shifts supply the inputs to CRI.
Color quality scale: A color-rendition metric designed to improve on CRI through revised samples and color-difference calculations. It offers an alternative score with different treatment of color differences.
Museum lighting: Lighting designed to display artworks while balancing visibility, appearance, and conservation. Color fidelity can shape how visitors perceive paintings and artifacts.
Metamerism: A phenomenon in which different spectral reflectances produce matching colors under one illuminant but not another. A source can alter color matches even when a CRI score seems acceptable.
Reference illuminant: A standardized light source or spectral distribution used as a comparison baseline in color measurement. CRI judges a test source against a reference chosen for its color temperature.
Gamut area index: A measure of how much a light source expands or contracts the area of colors rendered relative to a reference. CRI primarily measures fidelity and does not separately report gamut expansion or contraction.

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