A new type of LED developed at Rensselaer uses a novel omni-directional reflector.

A Rensselaer research team has created a new type of reflector that has dramatically improved LED (light-emitting diode) luminance. The National Science Foundation (NSF) recently awarded the research team a three-year, $210,000 grant to move the patented omni-directional reflector to market.

“We have developed an omni-directional reflector (ODR) for LEDs that will accelerate the replacement of conventional lighting used for a multitude of applications, such as lighting in homes, businesses, museums, airports, and on streets,” said Fred Schubert, the Wellfleet Senior Constellation Professor of the Future Chips Constellation at Rensselaer, who is heading the research effort. “The advance has implications ranging from major energy savings to contributing to a better environment and improving health.”

Made from semiconductor “chips,” LEDs increasingly are being used in traffic signals, automotive lighting, and exit signs. LEDs have the potential to use far less electricity and last much longer than conventional fluorescent and incandescent bulbs. However, current LEDs are not bright enough to replace most everyday uses of the standard light bulb.

“Only when the light generated is efficiently reflected inside the semiconductor can the brightness exceed that of standard lighting sources,” Schubert says. “With the ODR, which reflects light at nearly 100 percent — up to twice as much as previous reflectors — we now have an LED that could revolutionize today’s standard lighting.”

“With near-ideal LEDs, our nation could cut electricity consumption for lighting in half,” Schubert adds. “Lighting is the most common use of electrical energy, taking up about 25 percent of electrical energy consumption in the United States.”

In addition, an LED that emits higher-quality light has potential medical applications, such as alleviating sleep disorders, Schubert says.

LEDs are a “tunable” light source that can be adjusted to emphasize various wavelengths. “Tuning” LEDs to emit longer wavelength light (red) that mimics the setting sun, for example, could help those with insomnia sleep better. The circadian cycle, the 24-hour sleep-wake cycle in healthy humans, is controlled by the spectrum and intensity of light sources.

The ODR is a thin triple-layer coating that consists of a semiconductor, a dielectric material, and a silver layer.


Originally published in Rensselaer Magazine, Fall 2004

Published October 1, 2004