The Illuminating Engineering Society (IES) has published a Technical Memorandum (TM-30-15) defining a new pair of metrics intended to characterize the color rendition of light sources.
The Illuminating Engineering Society (IES) has published a Technical Memorandum (TM-30-15) defining a new pair of metrics intended to characterize the color rendition of light sources. We have a story in this issue on what could become a new industry standard measure that would replace CRI. I hope the International Commission on Illumination (CIE) can put aside its politics, do what's right for the solid-state lighting (SSL) industry, and endorse TM-30-15.
The issues with CRI are well known and factions within the lighting sector have sought to provide a more applicable replacement metric for years. The basic CRI metric uses an unrealistic set of color samples. It penalizes sources that make rich colors appear oversaturated even when designers/specifiers sometimes desire such performance. And CRI is simply not a good metric in terms of helping specifiers choose an LED-based product, or compare products, for a given application.
LEDs Magazine wholeheartedly endorsed the Color Quality Scale (CQS) metric that was considered for adoption by CIE technical committee (TC) 1-69 in 2012. At that link, you will find comments that suggest several reasons that were in part responsible for the failure of CQS in the CIE. At the time, some CIE members asked to respond to my column, a request that we eagerly granted. After the CIE column was submitted, the authors subsequently requested that we not run the response - citing internal disagreements about the issue within the CIE.
Why am I rehashing the CQS history? Primarily, I'm making the point that TM-30-15 acceptance is far from a sure thing in the CIE, although I believe the organization should adopt the work. TM-30-15 is clearly superior to CRI. The second gamut metric solves the problem of conveying light-source performance relative to color gamut. And the fidelity metric is based on a realistic color sample set.
TM-30-15 can only help the SSL industry move forward in deploying energy-saving technology. The new metrics will make it more straightforward for specifiers to deliver higher-quality lighting installations. And the new metrics are in no way skewed to a specific light-source type the way CRI was manipulated for fluorescent lighting.
For sure, the two-metric approach is not as convenient as the single-metric CQS would have been. But some in the industry, especially the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, have insisted that we need a two-metric approach to accurately characterize color performance.
I will wait anxiously for the actions of the CIE. As our CQS articles and comments make clear, the CIE is not charged with enabling the lighting industry but rather is purely a scientific body focused on lighting, imaging, photobiology, and other related issues. But the IES is charged with directly helping to improve the lit environment.
Still, the CIE wields enormous influence. I don't have the experience or knowledge to judge whether TM-30-15 meets the broad needs of the CIE as a way to characterize color rendition. But the organization should consider its influence and at a minimum endorse the new metrics for use by the lighting industry.
Maury Wright, EDITOR
