Lighting up time

A research team at Rensselaer Polytechnic Institute has created a new type of reflector that has dramatically improved the luminance of LEDs (light-emitting diodes).

A research team at Rensselaer Polytechnic Institute has created a new type of reflector that has dramatically improved the luminance of LEDs (light-emitting diodes).

The US 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, a Professor of the Future Chips Constellation at Rensselaer who is heading the research effort

Increasingly being used in traffic signals, automotive lighting, and exit signs, LEDs use far less electricity and last much longer than conventional fluorescent and incandescent bulbs. But current LEDs are not bright enough to replace the standard light bulb in most everyday applications.

‘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% – up to twice as much as previous reflectors – we now have an LED that could revolutionise today’s standard lighting,’ he adds.

The ODR is a thin triple-layer coating that consists of a semiconductor, a dielectric material, and a silver layer. Reports of the new reflector were published in the May 31, 2004, issue of the journal of Applied Physics Letters and last October in the IEEE (Institute of Electrical and Electronics Engineers) journal of Electron Devices Letters.

In addition to NSF funding, the researchers also have received $250,000 in the last two years from the US Defense Advanced Research Projects Agency to develop the new reflector.

Schubert, who won the 2000 Discover Magazine Award for his photon-recycling semiconductor LED invention, has helped to transform traffic signals and airport runway lighting through his numerous LED-based inventions. He holds appointments in the Department of Electrical, Computer, and Systems Engineering and in the Department of Physics, Applied Physics, and Astronomy at Rensselaer.

The recently-completed Future Chips Constellation, in which he is a senior professor, focuses on innovations in materials and devices, in solid state and smart lighting, and extends to applications such as sensing, communications, and biotechnology.

On the web