Color rendering index - Wikipedia, the free encyclopedia

Color rendering index - Wikipedia, the free encyclopedia

Color rendering index

From Wikipedia, the free encyclopedia

Emitted light spectrum determines the CRI of the lamp.

Color rendering index shown as Color Accuracy.

A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in color-critical applications such as neonatal care, photography and cinematography.^[1] It is defined by the International Commission on Illumination (CIE) as follows:^[2]

Color rendering: Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant

The CRI of a light source does not indicate the apparent color of the light source; that information is under the rubric of the correlated color temperature (CCT). In the pictures at right it can be noticed that the spectra have different structures; the incandescent lamp has a continuous spectrum, whereas the fluorescent lamp has separate lines in the spectrum due to emission of photons of discrete wavelengths by mercury.
The value often quoted as 'CRI' on commercially available lighting products is properly called the CIE R_a value, 'CRI' being a general term and CIE R_a being the international standard colour rendering index.
Numerically, the highest possible CIE R_a value is 100, and would only be given to a source identical to standardized daylight or a Black body (incandescent lamps are effectively blackbodies), dropping to negative values for some light sources. Low-pressure sodium lighting has negative CRI; fluorescent lights range from about 50 for the basic types, up to about 90 for the best tri-phosphor type. Typical LEDs have about 80+ CRI, while some manufacturers claim that their LEDs have achieved up to 98 CRI.^{[citation needed]}
CIE R_a's ability to predict color appearance has been criticized in favor of measures based on color appearance models, such as CIECAM02 and, for daylight simulators, the CIE Metamerism Index.^[3] CRI is not a good indicator for use in visual assessment, especially for sources below 5000 kelvin (K).^[4][5] A newer version of the CRI, R96_a, has been developed, but it has not replaced the better-known R_a general color rendering index.^{[citation needed]}