Evaluating Light Source Color Quality

In a recent webinar hosted by the U.S. Department of Energy Solid-State Lighting (SSL) Program, “DOE TM-30: What have we learned in the past two years,” the topic of TM-30-15 was once again discussed.

What is it?

For those of you who have not heard of TM-30, it’s a new method for evaluating a light source’s color rendition, published by the IES roughly two years ago. To evaluate average color rendition, TM-30 uses a two-metric system:

1. Color Fidelity (Rf) = the accurate rendition of color so they appear as they would under familiar (reference) illuminants. Scores are between 0-100.
2. Color Gamut (Rg) = the average level of saturation relative to familiar (reference) illuminants. Scores are between 60 and 140, when Rf > 60.

What’s the difference between TM-30, and the current method?

The current method was developed by the International Commission on Illumination’s (CIE’s) General Color Rendering Index R_a (CRI) and was developed more than 50 years ago, and has been unchanged in the last 40. It calculates the average of 14 color samples, while TM-30 calculates the average of 99 color samples taken from 105,000 real objects. Once the scores are calculated, they are represented in a visual graphic showing the hue and saturation changes:

It is not a required method for measuring CRI, but it is an approved one. If it proves to be more efficient, TM-30 may soon become the next required method. There are additional experiments being conducted to test chromaticity and illuminance effects to help us better understand the capabilities of TM-30.