page_title: Color rendering index
hierarchical_section_title: Color rendering index
caption_attribution_description: English: A very basic spectroscope made from a slit in cardboard and a prism. Even a simple instrument like this reveals a clear difference in the visible spectrum of an incandescent lamp and an arc-discharge–based low-energy-consumption lamp.
context_page_description: A color rendering index 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 and art restoration. It is defined by the International Commission on Illumination as follows:
  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 given by the correlated color temperature. The CRI is determined by the light source's spectrum. An incandescent lamp has a continuous spectrum, a fluorescent lamp has a discrete line spectrum; the incandescent lamp has the higher CRI.
  The value often quoted as "CRI" on commercially available lighting products is properly called the CIE Rₐ value, "CRI" being a general term and CIE Rₐ being the international standard color rendering index.
context_section_description: 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 and art restoration. It is defined by the International Commission on Illumination (CIE) as follows:
  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 given by the correlated color temperature (CCT). The CRI is determined by the light source's spectrum. An incandescent lamp has a continuous spectrum, a fluorescent lamp has a discrete line spectrum; the incandescent lamp has the higher CRI.
  The value often quoted as "CRI" on commercially available lighting products is properly called the CIE Rₐ value, "CRI" being a general term and CIE Rₐ being the international standard color rendering index.
  Numerically, the highest possible CIE Rₐ value is 100 and would only be given to a source identical to standardized daylight or a black body (incandescent lamps are effectively black bodies), 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 98 for the best multi-phosphor type. Typical LEDs have a CRI of 80 or more, while some manufacturers claim that their LEDs have achieved CRI up to 98.
  CIE Rₐ'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. 
  CRI is not a good indicator for use in visual assessment, especially for sources below 5000 kelvins (K). A newer version of the CRI, R96, has been developed, but it has not replaced the better-known Rₐ general color rendering index.
caption: Emitted light spectrum determines the CRI of the lamp. An incandescent lamp (middle image) has a continuous spectrum and therefore a higher CRI than a fluorescent lamp (lower image). The top image shows the setup of the demonstration from above.
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