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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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