What will the lighting industry be working on 10 years from now? Mark Rea of Rensselaer's Lighting Research Center is thinking farther ahead than most.
LEDs Magazine is running an interview with Rea from its December issue. He will keynote at the Strategies in Light conference in California in February, and he gave a preview of what he will discuss: monetizing the potential benefits of solid-state lighting.
The numerator
Rea begins by saying that the past and current concerns of the lighting industry, largely a commodity business, have been about cost, energy saving, and product longevity. Those elements have been the whole value proposition the industry has been selling. In Rea's view, those elements are the denominator of a total value proposition. Yes, you want to get costs and energy use down and lifetime up. But the numerator, where Rea says we will have to shift our attention, is the value that a lighting solution provides in an application.
The value could be improved color rendering, increased luminance on task, or better visual acuity provided by outdoor lighting. Determining this value, in a way that can be measured, is the task the SSL industry will face. The value depends entirely on what the goals of a lighting solution are, and Rea is eloquent and subtle in describing the several interacting perceptual systems -- channels -- in human vision that react in different ways to spectral tuning.
Metrics
When asked about the lighting industry's continuing reluctance to move to any metrics more inclusive than CRI for measuring color, Rea would not pick a winner from among the competing systems that have been put forward. He did stress the studies that the LRC has done pointing to the need for a two-metric system to characterize color adequately. "We have shown that," in addition to CRI, "if you don't also address the issue of saturation -- in other words, how vivid are the hues -- you will find people not preferring it." The LRC has proposed the Gamma Area Index as the second metric, and there are other proposals.
With a second metric comes a need to think differently about lighting controls. Why do we think about dimming only light intensity? Why not dim saturation? Rea points out that different cultures have very different preferences about color saturation --- Scandinavians prefer less saturated colors, while Indians prefer more saturation. A saturation dimming control would offer value internationally that lighting systems now lack.
HCL on steroids
Rea outlined some work the LRC has been doing in Sweden on a project named Healthy Home. It provides a glimpse of where the field of human-centric lighting (which we recently discussed) may be moving over the next decade. The work involves a personal light exposure device which a person wears all day. The device measures and records spectral exposures over time to be able to control lighting in the home at a later time. When the wearer returns home, the house's automation can provide the best and healthiest light in accordance with the individual's past exposure and future plans -- for example, if the wearer needs to rise earlier tomorrow for travel.
Rea covers other topics in this wide-ranging interview, and I urge you to read it. I look forward to hearing his ideas more fully fleshed out at SIL in Santa Clara next year.
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— Keith Dawson 
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