Editing Color rendering index (section)

{{Short description|Measure of ability of a light source to reproduce colors in comparison with a standard light source}}
{{Use American English|date=March 2025}}
{{Use mdy dates|date=March 2025|cs1-dates=ly}}
[[File:Simple spectroscope.jpg|thumb|upright=1.35|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.]]
[[File:AmbientLED.png|thumb|upright=1.35|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 [[color]]s of various objects faithfully in comparison with a natural or standard light source.

''[[Color rendering]]'', as defined by the [[International Commission on Illumination]] (CIE), is the effect of an [[Light#Light sources|illuminant]] on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference or [[standard illuminant]].<ref>{{cite web |url=http://www.cie.co.at/publ/abst/17-4-89.html |title=CIE 17.4-1987 International Lighting Vocabulary |access-date=February 19, 2008 |archive-url=https://web.archive.org/web/20100227034508/http://www.cie.co.at/publ/abst/17-4-89.html |archive-date=February 27, 2010 }}</ref>

The CRI of a light source does not indicate the apparent color of the light source; that information is given by the [[Color temperature|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 [[Emission spectrum|line spectrum]]; implying that the incandescent lamp has the higher CRI.

The value often quoted as "CRI" on commercially available lighting products is properly called the CIE R<sub>a</sub> value, "CRI" being a general term and CIE R<sub>a</sub> being the international standard color rendering index.

Numerically, the highest possible CIE R<sub>a</sub> value is 100 and would only be given to a source whose [[spectrum]] is identical to [[Solar spectrum|the spectrum of daylight]], very close to that of a [[black body]] (incandescent lamps are effectively black bodies), dropping to negative values for some light sources. [[Low-pressure sodium light]]ing has a negative CRI; [[fluorescent light]]s range from about 50 for the basic types, up to about 98 for the best multi-phosphor type. Typical white-color [[LEDs]] have a CRI of 80 or more, while some manufacturers claim that their LEDs achieve a CRI of up to 98.<ref>{{Cite web |url=http://www.ledengin.com/files/products/LZC/LZC-00GW00.pdf |title=LZC-00GW00 Data Sheet |date=March 16, 2015 |website=ledengin.com |publisher=LED ENGIN |archive-url=https://web.archive.org/web/20170105235216/http://www.ledengin.com/files/products/LZC/LZC-00GW00.pdf |archive-date=January 5, 2017 }}</ref>

CIE R<sub>a</sub>'s ability to predict color appearance has been criticized in favor of measures based on [[color appearance model]]s, such as [[CIECAM02]] and for [[daylight]] simulators, the CIE [[metamerism index]].<ref>{{citation |first2=János |last2=Schanda |first1=Norbert |last1=Sándor |journal=Lighting Research and Technology |volume=38 |issue=3 |title=Visual colour rendering based on colour difference evaluations |date=September 1, 2006 |pages=225–239 |doi=10.1191/1365782806lrt168oa }}.<br />Conference version of this article:<br />{{citation |first2=János |last2=Schanda |first1=Norbert |last1=Sándor |title=Visual colour-rendering experiments |journal=AIC Colour '05: 10th Congress of the International Colour Association |year=2005 |pages=511–514 |url=http://www.knt.vein.hu/staff/schandaj/SJCV-Publ-2005/521.pdf |archive-url=https://web.archive.org/web/20110721114551/http://www.knt.vein.hu/staff/schandaj/SJCV-Publ-2005/521.pdf |archive-date=July 21, 2011}}</ref> CRI is not a good indicator for use in visual assessment of light sources, especially for sources below 5000&nbsp;[[kelvin]] (K).<ref>{{citation
 | last1 = Guo
 | first1= Xin
 | last2 = Houser
 | first2= Kevin W.
 | year = 2004
 | title = A review of colour rendering indices and their application to commercial light sources
 | journal = Lighting Research and Technology
 | volume = 36
 | issue = 3
 | pages = 183–199
 | doi = 10.1191/1365782804li112oa
 }}</ref><ref name="CIE1995">{{citation
 |author       = CIE
 |series       = Publication 13.3
 |year         = 1995
 |url          = http://www.cie.co.at/publ/abst/13-3-95.html
 |title        = Method of Measuring and Specifying Colour Rendering Properties of Light Sources
 |isbn         = 978-3-900734-57-2
 |publisher    = Commission Internationale de l'Eclairage
 |location     = Vienna
 |access-date  = January 19, 2008
 |archive-url  = https://web.archive.org/web/20080103162323/http://www.cie.co.at/publ/abst/13-3-95.html
 |archive-date = January 3, 2008
 }}
 (A verbatim re-publication of the 1974, second edition. Accompanying disk [http://www.cie.co.at/publ/abst/d008.html D008: Computer Program to Calculate CRIs]. {{Webarchive|url=https://web.archive.org/web/20080327023340/http://www.cie.co.at/publ/abst/d008.html |date=March 27, 2008 }})</ref> New standards, such as the [[IES TM-30]], resolve these issues and have begun replacing the usage of CRI among professional lighting designers.<ref>Illuminating Engineering Society. 2018. ''IES Method for Evaluating Light Source Color Rendition, IES Technical Memorandum (TM) 30-18''.</ref> However, CRI is still common among household lighting products.