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Bierman and his colleagues subsequently found that normal light levels could be reduced by as much as 30 percent for periods of time, while remaining acceptable to 70 percent of office workers. Moreover, when a building’s occupants learned about the benefits of the energy-saving concept, 90 percent found the reduced light levels satisfactory. “There is a difference between what people can detect and what they will accept,” Bierman says. Discovering that difference made the concept commercially viable. Now on the market, PowerSHED won an innovation award this year at LightFair International, the industry’s biggest American trade show.

Solid Solutions

Good lighting demands adaptability. To this end, LRC has helped to develop alternative, highly flexible lighting systems that employ the light-emitting diode (LED). LEDs are essentially semiconductors that create light when an electrical current passes through them. LEDs are classified as a “solid-state light” source because the light emitted comes from a solid semiconductor. White light LEDs combine a light-emitting semiconductor with a phosphor, a chemical substance that glows when stimulated by optical radiation.

Today, LEDs are commonly found in exit signs and traffic signals. The potential advantages of LEDs include better durability, less radiant heat, and modularity—LEDs can be an arrangement of smaller lights, as with traffic signals. But presently LEDs do have drawbacks, including price and the amount of light generated.

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The Scattered Photon Extraction method generates up to 60 percent
more light output than typical white LEDs.

LEDs have traditionally been indicators, not illuminators—lights that can be seen but don’t illuminate the area around them. White-colored LEDs need to become more powerful and less expensive for widespread interior use. That’s the problem LRC researchers, led by Director of Research Nadarajah Narendran, tackled in 2005, by a method called Scattered Photon Extraction (SPETM). This places the phosphor away from the core of the LED and changes the geometric arrangement of the device, allowing more photons to escape the fixture, thus making the white LED up to 60 percent brighter.

SPE is being incorporated into products soon to be on the market, and it could help bring the LED into homes and offices where it could be used in novel ways. Inside the Gurley Building, LRC researchers have created a mock-up room lit entirely by LEDs, which are embedded in modular wall panels and can be moved around interchangeably. No longer would you have to hunt for a light outlet or read a magazine only at the end of the couch nearest the lamp. “We are making a mistake as a community if we try to get a new technology to mimic an old technology,” says Narendran. “Instead of hanging these things off the existing fixtures, we’re making lighting part of the building materials, like a window. LEDs can become part of the whole structure.”

Overhauling home lighting could be a do-it-yourself project, too. “The motivation is not just that it can become three times more efficient in a few years, but it’s easy, because now you only have to pay for the new piece of lighting,” adds Narendran. “And it’s good for the environment.” Such large transformations don’t come easily. “We believe a change in building infrastructure will probably be necessary to capture the full benefits of solid-state lighting,” says Rea.

Still, many of the inherent benefits of LED lighting systems can be applied widely now. The FAA has asked the center to expand the use of LEDs as lighting for airport runways, while Boeing approached the LRC to explore their application in its forthcoming plane, the 787 “Dreamliner.” An upper floor of the Gurley Building sports an airplane-cabin mock-up and simulator devices to examine visibility issues for passengers. For both the FAA and Boeing, LRC “was like one-stop shopping,” says Narendran. “We could cover the technology aspect, the human aspect, and the design aspect.”

Still, he preaches patience with LEDs. “There’s no one application that represents the day everything changes,” says Narendran. “A lot of little breakthroughs can be made, and over the next five years we will see different applications showing up on our walls.”

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Rensselaer (ISSN 0898-1442) is published in Spring, Summer, Fall, and Winter by the Office of Strategic Communications and External Relations, Rensselaer Polytechnic Institute, Troy, NY 12180-3590. Opinions expressed in these pages do not necessarily reflect the views of the editors or the policies of the Institute. ©2008 Rensselaer Polytechnic Institute.