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 because the All LED Lighting site has gone dark. This material is Copyright 2013-2015 by UBM Americas.


Xicato Shoots for Vibrant

LED light sources can be engineered to produce nearly any desired power spectrum in visible light. So why should we stop at emulating the light of older technologies?

The earliest white-light LEDs were disappointing to most people who tried them. They weren't very bright, and they tended to produce a cold, blue-ish light that rendered colors oddly and made flesh tones look sallow. The industry scrambled to produce devices that could generate light closer to what people were accustomed to: warm white light on the blackbody spectrum, or not far from it. Light at various points along that spectrum corresponding to an incandescent filament burning in halogen gas, to sky light, to filtered sunlight, to sunset light.

We have discussed the limitations of the color rendering index (CRI) scale, and debated which (if any) metric deserves to supplant it. The biggest problem with CRI may not be its reliance on the rendering of pastel colors to the neglect of saturated ones. The bigger problem may be in its framing that leads us to accept 100 CRI as "perfect" color rendering -- when all it is is color rendering most exactly like that of an incandescent source.

Can we do better?
Can light produced by an LED improve in some dimensions on anything an incandescent or a halogen can generate? Can it make objects look more eye-catching, more appealing, more vibrant than they could possibly look under incandescent lighting? Xicato embarked on a research program to find out, and the company seems to believe that the new addition to its light portfolio, dubbed Vibrant, answers those questions in the affirmative.

The gamut area of Xicato's Vibrant is below that of blackbody, not contiguous with it, so its CRI is less than 100; but its gamut area is larger and thus its GAI is higher.
(Source: Xicato)

Xicato sponsored research carried out by Colette C. Knight, Ph.D, an independent lighting specifier. A total of 60 subjects -- 20 ordinary people and 40 expert lighting designers -- were exposed to mock commercial displays lit by one or a combination of six light sources. Of those sources, two were from Xicato's then-existing commercial product line, XSM Standard Series and Artist Series, with CRI > 80 and CRI > 95, respectively. The other four sources were experimental modules with color points that were below the blackbody locus (BBBL) and with a Gamut Area Index (GAI) that was larger than that for the existing products. (See the table at the bottom of page 2 of this summary research report from Dr. Knight.) This research informed the design of what became the Vibrant Series.

Advantage: retail
The researchers designing the BBBL sources were aiming for light that increased the "vibrancy" and "pop" of colored objects beyond the reach of incandescent light, and increased the detail in the rendering of white objects. The objective was to produce an LED source that can give brick-and-mortar retail shops an advantage that cannot possibly be matched by an online experience. Xicato believes it can offer that advantage with Vibrant.

Are you aware of other experimental or commercial efforts to improve on nature and the incandescent, in terms of the psychological effects of color rendering? Let's hash it out in the comments.

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