The lighting industry has long known of shortcomings in the use of Color Rendering Index (CRI) to describe the color quality of white light. The US-based National Institute of Standards and Technology (NIST) has developed a new Color Quality Scale (CQS) that it believes to be superior to CRI.
NIST has published a paper detailing the CQS methodology, and is proposing its adoption by the Commission on Illumination (CIE) Technical Committee (TC) 1-69.
In his weekly Postings email newsletter, US Department of Energy (DOE) Lighting Program Manager Jim Brodrick heartily endorsed the CQS approach. But Brodrick and the NIST both fear that the CQS isn't getting a fair review by the "Colour rendition by white light sources" TC 1-69 committee.
Brodrick wrote, "I've had an opportunity to visit NIST's color laboratory and see the CQS in action, and I can tell you it fills the bill. Regardless of the type of light source, the CQS represents the color rendering qualities of white light more accurately than the CRI and is a far better predictor for colors that have a high red content, such as skin color and wood finishes – which is one of the CRI's major weaknesses."
Where CRI relies on a evaluation of how a white light source illuminates eight pastel colors, CQS uses 15 colors. Moreover the CQS color set includes samples with much deeper color – such as deep reds where CRI proves especially inaccurate.
The authors of the NIST paper note that they have widely distributed to solid-state-light (SSL) vendors a spreadsheet that calculates CQS, and that CQS is gaining support in the SSL industry. But the authors point out that the TC is leaning toward a "pure fidelity metric very similar to CRI."
The primary purpose of the NIST paper is to encourage comments from the SSL community to the TC. The paper notes that the SSL industry is not well represented in the TC. Industry players that wish to make a comment can email then to [email protected].
Brodrick wrote, "In my mind, and to many others in the field, switching to the CQS should be a slam-dunk." Brodrick points out that the TC decision will have considerable impact on SSL for years. With such a decision at stake, industry participants with a point to make to the TC should send a comment.
