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
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
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, LEDs Magazine
This opinion piece was first published in LEDs Magazine.
- Lux magazine is hosting a special webinar on this subject, entitled ‘Introducing TM-30 – the new way to measure colour rendering’. In this on-line seminar, you’ll learn how the new metric works better with LEDs, how to understand it and how to use it. You’ll learn why we need to look at CRI, how TM-30 will improve CR metrics, how TM-30 will work and what TM-30 means for specifiers. The presenter is Peter Raynham, lighting expert and senior lecturer at the Bartlett School of Architecture at University College London. It takes place on Wednesday 3 February at 7am Central US, 1pm United Kingdom, 5pm UAE and 9pm Hong Kong. To register for free, click here.