Long-sought replacement for CRI color metric that more accurately characterizes SSL and legacy light sources is at hand in the IES, and has been proposed to the CIE.
The Illuminating Engineering Society (IES) has published a new Technical Memorandum — TM-30-15 entitled "IES Method for Evaluating Light Source Color Rendition" — that promises to supplant CRI as a color metric. TM-30 relies on separate fidelity and gamut metrics, as well as a set of color samples that is more representative of real-world objects as opposed to the pastel samples that were primarily used for the baseline CRI metric that was sometimes called Ra. The new color metric is intended to fairly and accurately characterize both LED-based solid-state lighting (SSL) and legacy sources.
We first reported on the IES color metric work back in April and indeed the new publication is largely aligned with our earlier story. The new Rf fidelity metric is similar to CRI although based on the new color samples. The new Rg gamut metric is evolved from the Gamut Area Index (GAI) work done original by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute.
The IES committee behind TM-30 was led by Michael Royer of the Pacific Northwest National Laboratory (PNNL), part of the US Department of Energy (DOE) SSL organization. The DOE will be holding two webcasts in September covering the basics of the new document first and the underlying math and color science second.
While the IES is clearly an influential organization, the publication of TM-30-15 and its color metric information will not automatically make the work an industry standard. The International Commission on Illumination (CIE) will also have a say in the matter and is the standards body behind CRI. Previously, the CIE refused to adopt the CQS (Color Quality Scale) metric that had been developed within the auspices of NIST (National Institute of Standards and Technology) in the US.
The DOE said that TM-30-15 has been proposed to CIE. We will await action by that organization. Meanwhile, TM-30 clearly provides an improved manner to evaluate light-source performance in the color area.