College of Engineering Magazine- Fall 2000

Illumination Central

By Taylor McNeill

IT'S A TINY LIGHT, BUT ITS FUTURE IS BRIGHT.

Fred Schubert, a professor in the Electrical and Computer Engineering Department, is in his lab on the eighth floor of the Photonics Center holding a single light-emitting diode. Not too remarkable, you say, until you look closer. Around its edges, the LED shines blue and red, but at its center, the color is clearly white, the first of its particular kind in the world. Could this little LED be the beginning of the end for the 100-plus-year reign of the light bulb?

It's a long road from a single diode in the lab to the shelves of Home Depot, but Schubert believes that his white-light LED, for which he has a patent pending, is the future of illumination. Conventional light bulbs, of course, expend most of their energy as heat rather than light, and break easily. By contrast, LEDs are much more efficient users of energy, are sturdy, and can shine for years. If LEDs could be made to emit white light, the market would be huge.

While many companies, such as General Electric and Phillips, are trying to develop white-light LEDs, Schubert and his colleagues were the first to devise what he calls a PRS-LED, a photonrecycling semiconductor light-emitting diode. With a blue-light LED made from gallium indium nitride as its base, the PRS-LED sends blue-light photons through a second light-emitting semiconductor to which it is bound. There, part of the light is absorbed and reemitted (or recycled) as yellow light. The resulting blend of two-color light creates what the human eye sees as white light.

"The minimum requirement to get white is that you have two complementary colors. We used only two colors, but we are now thinking about a three-color scheme," Schubert says. The more colors blended together, the closer the approximation of natural light-and thus better rendering of colors. "With three colors, it's basically comparable to fluorescent light. With two colors, the color rendering isn't as good as fluorescent light, but the efficiency is higher." The market for basic two-color white-light LEDs would be in low-end applications such as outdoor illumination of streets and emergency exits, Schubert says. Add another color-or two-and the quality of light goes up.

For his invention, Schubert won a Discover Award for Technological Innovation this year-and a few phone calls from interested companies, including an auto supplier. As cars start to employ red LEDs for brake lights, white-light LEDs for interior illumination could be next.

The LED market is growing about 10 to 15 percent every year, and whitelight LEDs should boost that even more when they become commercially available, Schubert says. "Up until a few years ago, LEDs were mainly used as indicator lights. The purpose of the LED was to convey information, not illumination. Now ifs changing, and the potential is just fantastic."