A Review Of Ten Color Rendering Metrics

Here is a look at ten color rendering metrics:

CRI / Ra: The most used Color Rendering Index (CRI), is based on averaging the first 8 test colors (R1–R8), out of the 15 tested, reported as a 0–100 score. It is a measure relative to a reference source, either sunlight or an incandescent / halogen lamp. CRI(Ra) measurements can only be compared among light sources with the same CCT.

Extended CRI / Re: Is an expanded metric used to measure a light source’s color accuracy across 15 distinct test color samples, rather than just the first eight. Ra only averages eight low-saturation pastel colors (R1–R8), while Extended CRI includes seven additional highly saturated and specialized colors (R9–R15) to provide a much more thorough, real-world assessment of light quality.

R9: A supplemental CRI value for strong red rendering; it is not part of the standard CRI average (Ra) but is widely used because red performance matters for skin, food, and materials.

TM-30 Rf: The fidelity index in IES TM-30, intended to describe how closely colors match a reference source on a 0–100 scale. Rf measures and averages 99 color evaluation samples (CES).

TM-30 Rg: The gamut index in TM-30, centered at 100. Values above 100 indicate increased saturation, and below 100 indicate reduced saturation.

TM-30 Color Vector Graphic: A visual metric showing hue-by-hue shifts in color rendering across 16 bins.

CQS: Color Quality Scale, a broader rendering metric developed by NIST to address CRI limitations.

TLCI: Television Lighting Consistency Index, used for how light renders colors on camera rather than to the human eye.

SSI: Spectral Similarity Index, which compares a source’s spectrum against a reference spectrum.

Rw: A nonstandard “whiteness” metric some manufacturers use to describe how neutral or clean whites appear.

For specifying architectural lighting, the most common shorthand is still CRI (Ra) plus R9, but TM-30 gives a more complete picture because it separates fidelity from saturation, and measures and averages fidelity across 99 color evaluation samples rather than 8 or 15. For applications in front of a camera, TLCI or SSI can matter more than CRI.

More information on color rendering metrics is available here.

David Shiller

David Shiller is the Publisher of LightNOW, and Senior Business Development Consultant at Capacity Consulting, a North American consulting firm providing business development services to advanced lighting manufacturers. The ALA awarded David the Pillar of the Industry Award. David has been co-chair of the ALA’s Engineering Committee since 2010. David established MaxLite’s OEM component sales into a multi-million dollar division. He invented GU24 lamps while leading ENERGY STAR lighting programs for the US EPA. David has been published in leading lighting publications, including LD+A, enLIGHTenment Magazine, LEDs Magazine, and more.

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