This post was written by Keith Dawson for UBM Tech’s community Web site All LED Lighting, sponsored by Philips Lumileds. It is archived here for informational purposes only because the All LED Lighting site may go dark at any time. This material is Copyright 2013-2015 by UBM Americas.


Getting Up to Date With Color Science

In our live chat yesterday, color scientist Rachel Schwen caught us up on recent research and the prospects for a rendering standard to supplant the venerable Color Rendering Index.

The discussion sprang out of a recent Monday Roundup, in which we discussed the Color Rendering Index (CRI), its limitations, and the candidates for eventually replacing it. A leading contender is (or was) the Color Quality Scale (CQS). Asked, "When will CQS be codified and in general use?" Schwen replied:

I don't think it will be in its current form. Its creator and champion, Wendy Davis and her coauthor Dr. Ohno, are making headway but its not widely accepted as a standard in the color community. Plus Wendy has moved on to an academic life so she's not likely to push it. Also keep in mind that it has never been published in a peer-reviewed journal.

Other color quality metrics
CQS was introduced by the National Institute of Standards and Technology in mid-2010, within weeks of the unveiling by the ASSIST alliance of a two-volume description of that organization's recommendation for specifying the color properties of light sources for retail merchandising. ASSIST recommended supplementing CRI with a metric called gamut area index, or GAI. (ASSIST is a collaboration of manufacturers and research organizations focused on identifying and overcoming barriers to the adoption of solid-state lighting.)

Blogger Dennis McCarthy asked a question that elicited more details from our color-science expert guest. Dennis asked, "Is it fair to say that CQS and CRI-GAI all have their places as metrics but now people are becoming more discerning in which metric to use, and when and why?" Schwen replied:

I think that is fair. Consider that there are at least 6 recent color rendering papers: CQS, CRI-CAM02UCS, Smet, and Bodrogi (a 6-metric scale). They all have their merits but as far as widespread use, I think the industry prefers a 1-number scale. It's just easier to educate consumers and [to] put on packaging.

Color temperature and the artificiality of light
Schwen touched on a subject we explored in some depth in our recent chat with scotobiologist Robert Dick: namely, the effects of artificial lighting on creatures (such as ourselves) evolved under natural sunlight. As we discussed the deleterious effects of the blue components of artificial light, and whether humans might adapt over time to such lighting, Schwen noted:

I think there is a community [of color specialists] that embraces higher color temperatures in interior lighting, work environments, etc. Ott Lite [with a CCT between 5000K and 5800K] continues to do well with its task lighting for people who craft or sew. I think people still will prefer warmer temperatures for home lighting, but that may migrate in future generations. When my son grows up he will likely never experience an incandescent light in our house and it may change his expectation of lighting.

Many thanks to Rachel Schwen for sharing her expertise with us. All of us participating in the chat came away with more knowledge of and insight into the state of color science now, and plenty of background reading to catch up on.

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