What’s the difference between CRI and TM-30 Color Rendition Metrics?

The Color Rendition Index (CRI) was the first metric developed to characterize how colors appear under various light sources. It is the most well-known color rendering metric among both the scientific/engineering community and the broader lighting design and consumer markets.

The ANSI/IES TM-30 Standards are an internationally accepted set of guidelines for characterizing the color rendition (color rendering) performance of virtually any light source. These standards were developed to encompass more aspects of light appearance, and to provide a more accurate measure of newer light sources such as LEDs.

Comparing CRI vs. TM-30

Although CRI is a familiar and long-standing color rendering metric, lighting experts have long noted its limitations. CRI was developed when incandescent and fluorescent light predominated, and concerns persist about CRI’s ability to represent solid-state lighting. LEDs as a lighting technology did not start to become mainstream until roughly 2012. With today’s high-quality LEDs a difference of just 4-5 points in the CRI (e.g., 80 CRI vs 85) is very noticeable.

CRI also represents only color fidelity—accuracy—not the more subjective quality of perception—how well it looks to the human eye. CRI, therefore, can be particularly problematic for LEDs. LEDs can produce light that produces a poor CRI score, but that looks good to humans. In a Rensselaer Polytechnic study, participants were asked to rate fruit under different lighting sources. Participants found LED lighting vivid and the incandescent natural. Yet the incandescent had a CRI rating of 100, the LED only 40¹ .

CRI combined with R9 has become a commonly used metric. While this is yields better results than using only CRI, the TM-30 system has much more detail than this single-dimension approach.

IES asserts that the TM-30 scoring system is both more accurate due to its use of 99 samples, and more relevant for LEDs: “IES R_f uses a modern color space (CAM02-UCS)—with improved uniformity and a more accurate chromatic adaptation transformation—and an optimized set of color samples representative of real-world objects, making it especially relevant when average color fidelity is an important consideration”². The IES recommends that lighting professionals transition to IES R_f and acknowledges the usefulness of publishing CIE R_a values alongside R_f ³.

To learn more, refer to the Help Center articles:

FAQ -> Color Quality Metrics

White Papers -> Achieving Optimal Color Rendition with LEDs

REFERENCES

1. “PS-11-18: IES Position on TM-20-18, IES Method for Evaluating Light Source Color Rendition.” Illuminating Engineering Society, October 9, 2018.
2. Davis, Wendy & Ohno, Yoshi. (2010). “Color Quality Scale.” Optical Engineering 49(3) March 2010. DOI 1117/1.3360335

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