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Lighting Design Glossary

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Color Rendering Index (CRI)
General Color Rendering Index

(Term of photometry)

A method for describing the effect of a light source on the color appearance of objects, compared to a reference source of the same color temperature (CCT). It serves as a quality distinction between light sources emitting light of the same color (metamer). The highest CRI attainable is 100. Typical cool white fluorescent lamps have a CRI of 62. Lamps having rare-earth phosphors are available with a CRI of 80 and above.

In a daylighting context, the color rendering index defines the spectral transmissive quality of glasses or other transparent materials. In this case, values of 95 or better are considered acceptable.

The general color rendering index Ra is a measure of the average appearance of eight standardized colors chosen to be of intermediate saturation and spread throughout the range of hues. If a color rendering index is not qualified as to the color samples used, Ra is assumed.


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