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Electronic Design

Project Green Light

While the telegraph is but a memory and steam locomotives have mostly chugged into history, the incandescent light bulb—and other similarly ancient lighting technologies—still burn on. But perhaps not for much longer.

Artificial lighting's future lies in solid-state devices, particularly light-emitting diodes (LEDs) that promise to burn just as brightly, but last longer and consume far less energy than conventional lights (see the Figure). "Substantial reductions in the nation's dependence on primary energy imports will be possible once highly efficient solid-state light sources replace wasteful incandescent and fluorescent lighting," says Christian Wetzel an associate professor of physics at Rensselaer Polytechnic Institute in Troy, NY.

Wetzel is leading a research team that's working to solve one of the last roadblocks to developing an LED lighting source that's not only cheap, long lasting and energy efficient, but pleasing to the human eye. The technology that's the most promising candidate, says Wetzel, is a white-light system constructed from modules containing red, blue and green LEDs. "These types of luminaries would parallel, very much, what the transistor has done to the radio tube," he claims.

While it's not difficult to produce high-quality, efficient red and blue LEDs, a practical green technology has so far eluded researchers. Green light is an essential piece of the LED lighting puzzle, however, since it provides a necessary counterbalance to the other colors. Removing green from the lighting equation leaves a garish hue that's more suited for a disco or strip club than a home or office.

Green LEDs can be made quite easily by adding indium to the gallium nitride materials that are used to create blue LEDs. Unfortunately, the LEDs made this way are far too dim for use in everyday lighting applications. "It has been easily possible to make a good blue LED, but for a green it is just exponentially more complicated," Wetzel says.

The problem with adding indium to gallium nitride is that the indium tends to segregate and cluster in areas of the material that contain defects. Wetzel believes he can improve green LED technology by taking advantage of the piezoelectric effect, which allows some materials to produce an electrical field when pressure is applied. By controlling this effect, Wetzel and his colleagues hope to develop a process that allows green LEDs to convert electricity into light more efficiently. "It may be difficult to make \[the material\] homogeneous, but the driving force is actually the piezoelectric field itself," Wetzel says.

Wetzel believes that his green LED research could lead to a commercially available LED lighting module within three to five years. "Eventually, it will be available in Home Depot," he predicts.

The U.S. Department of Energy's Solid-State Lighting program is underwriting Wetzel's research with a $1.8 million grant. The team is also working with Kyma Technologies, a gallium nitride substrates developer located in Raleigh, NC, and Crystal IS, a Green Island, NY-based producer of single-crystal substrates for the production of optoelectronic devices.

Replacing existing lighting technologies with solid-state devices promises immediate and substantial economic benefits. "The Department of Energy estimates customer savings of $115 billion by the year 2025 and a 10 percent reduction in greenhouse gases," Wetzel says. "Making lighting more efficient is one of the biggest challenges we face."

TAGS: Components
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