What is Color Rendition (Color Rendering)?

Color rendition (also commonly referred to as color rendering) is the effect of light on the color appearance of objects—how the color is perceived by humans. The International Commission on Illumination (CIE) publishes an International Lighting Vocabulary that defines color rendering as the “effect of an illuminant [light source] on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant.” Put more simply, the color rendition characteristics of a light source (which can be measured) determine how accurately the color of an object appears to our eyes under that light source.

To determine accuracy, the light source is compared to a standard source, called the reference illuminant¹. Each CCT has a defined reference illuminant. When a light source is under evaluation (the test light source) it is compared to the reference illuminant that matches its CCT.

Models for Color Rendition Accuracy

Various models exist to describe the color rendition capabilities of light sources. Each model attempts to accurately describe what the human eye will perceive. These models typically characterize one or more of three key aspects color rendition:

1. Color Fidelity: the accurate rendition of colors so that they appear as they would under familiar reference illuminants
2. Color Preference: Rendition of objects such that they appear pleasant, vivid, or flattering
3. Color Discrimination: the ability of an illuminant to allow an observer to distinguish between colors when viewed simultaneously.²

Lighting source developers and manufacturers use evaluation systems to rate light output. Designers, architects, and others use models to specify the desired lighting for a setting. All color rendition models are voluntary, with no prescribed standards for use. An early and still commonly used model is the CRI, developed by the CIE as a measure of color fidelity. The CRI standard was first introduced in 1965 and has been improved over the years, most recently in 1995. It is this version, the CIE 13.3-1995 General Color Rendering Index R_a (commonly referred to as the CRI), that is in use today.

Other models to measure color rendition include the gamut area index (GAI), which measures color saturation, the Color Quality Scale (CQS) addresses “chroma” (saturation) of light source color, and the ANSI/IES TM-30 which measures both fidelity and gamut. There are various rendition classification models; we will discuss several of the most common methods below.

NOTES & REFERENCES

1. Reference illuminants are a set of standardized SPD data sets that represent real light sources such as incandescent light, sunlight, fluorescent light, etc. The reference illuminants—also called standard illuminants—provide common comparison points for light sources of all kinds. For more information refer to the Help Center article What is a Standard Illuminant (Reference Illuminant)?
2. Hauser, K., et al., “Review of Measures of light-source color rendition and considerations for a two-measure system for characterizing color rendition,” Optical Society of America, Optics Express, Vol 21(8), April 22, 2013. DOI: 10.1364/OE.21.010393

To learn more, refer to the Help Center articles:

FAQ -> Color Quality Metrics

White Papers -> Achieving Optimal Color Rendition with LEDs

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