Here is a look at ten color rendering metrics:

1 – 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.

2 – 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.

3 – 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.

4 – 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).

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

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

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

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

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

10 – 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: https://www.energy.gov/cmei/ssl/color-and-spectrum

Author: David Shiller
Source: https://www.lightnowblog.com/2026/06/a-review-of-ten-color-rendering-metrics/