[ Back to EurekAlert! ] Public release date: 26-May-2005
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Contact: Theresa Bourgeois
bourgt@rpi.edu
518-276-2840
Rensselaer Polytechnic Institute

Solid-state lighting sources getting more energy efficient and smart

Rensselaer researchers detail potential for smart lighting in Science

Troy, N.Y. "Smart" solid-state light sources now being developed not only have the potential to provide significant energy savings, but also offer new opportunities for applications that go well beyond the lighting provided by conventional incandescent and fluorescent sources, according to E. Fred Schubert and Jong Kyu Kim of Rensselaer Polytechnic Institute.

In an article published May 27, 2005 in the journal Science, the authors describe research currently under way to transform lighting into "smart" lighting, with benefits expected in such diverse fields as medicine, transportation, communications, imaging, and agriculture. The ability to control basic light properties -- including spectral power distribution, polarization, and color temperature -- will allow "smart" light sources to adjust to specific environments and requirements and to undertake entirely new functions that are not possible with incandescent or fluorescent lighting.

For example, "smart" solid-state light sources have the potential to adjust human circadian rhythms to match changing work schedules, to allow an automobile to imperceptibly communicate with the car behind it, or to economically grow out-of-season strawberries in northern climates, according to Professors Schubert and Kim.

Solid-state lighting sources such as light-emitting diodes (LEDs) already offer energy savings and environmental benefits compared to traditional incandescent or fluorescent lamps, say Schubert, the Wellfleet Senior Constellation Professor of the Future Chips Constellation at Rensselaer, and Kim, a post-doctoral fellow. Fundamental principles of physics place far greater limits on the efficiency of incandescent and fluorescent lights than on solid-state lights. In theory, solid-state devices with perfect materials and designs would require only 3 watts to generate the light obtained from a 60-watt incandescent bulb.

Solid-state sources potentially could cut in half the 22 percent of electricity now consumed by lighting. Traffic lights using LEDs, for example, use only one-tenth the power of signals using incandescent lamps. Further development of solid-state sources to replace traditional lighting will reduce energy consumption and dependency on oil and decrease emissions of greenhouse gases, acid-rain-causing sulphur dioxide, and mercury.

However, it is the possibility of controlling such basic properties of solid-state lighting as spectral content, emission pattern, polarization, color temperature, and intensity that gives these light sources the ability to provide entirely new functions. For example:

To achieve these benefits, according to Schubert and Kim, improvements are needed in materials, device design and fabrication, and packaging of solid-state components into lamps and luminaires. Researchers must learn, for example, how to grow ultraviolet, green, yellow-green, and yellow emitters with improved internal quantum efficiencies.

To efficiently extract light from the LED chip and package, new methods are needed such as the omni-directional reflectors recently developed by a team led by Schubert. Several strategies are being pursued to increase the power per package, including scaling up the chip area, scaling up the current density, and increasing the maximum allowable operating temperature.

Scaling is particularly interesting, as it is reminiscent of the successful scaling in silicon technology that for decades has shrunk computers while increasing their power, say Schubert and Kim. The scaling up of LED chip size and current density will substantially reduce costs, bringing LEDs into offices, homes, and, perhaps, even dining room chandeliers, the authors say. In addition, low-cost availability of solid-state lighting devices will contribute to the development of a wide variety of totally new smart lighting functions.

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About Rensselaer
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological university. The university offers bachelors, master's, and doctoral degrees in engineering, the sciences, information technology, architecture, management, and the humanities and social sciences. Institute programs serve undergraduates, graduate students, and working professionals around the world. Rensselaer faculty are known for pre-eminence in research conducted in a wide range of fields, with particular emphasis in biotechnology, nanotechnology, information technology, and the media arts and technology. The Institute is well known for its success in the transfer of technology from the laboratory to the marketplace so that new discoveries and inventions benefit human life, protect the environment, and strengthen economic development.



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