April 27, 2006. Copyright 2006, Graphic News. All rights reserved

New glow in quest for white-light LED
By Mark Rutter

LONDON, April 27, Graphic News:  With their 20-plus year lifespan, a warm lighting effect and impressive energy efficiency, LEDs -- or light emitting diodes -- are rapidly becoming the light source of choice in a whole variety of everyday applications. From Christmas tree lights, car brake lamps, traffic lights and bicycle lamps to illumination of buildings, what started as the little glowing red or green indicator lights on electronic equipment are set to illuminate our homes. Or at least they would be if the technical hurdles of producing a pure white-light LED could be overcome.

In these times of higher energy bills and growing concern over carbon dioxide emissions, the development of energy-efficient technologies has gained new momentum. One of the most promising advances has been the use of LEDs as replacements for coloured incandescent lighting. The inefficiency of conventional incandescent bulbs is down to the fact that they must reach temperatures of 2,000¡C before emitting light, so most of the energy used is lost as heat.

Lower energy and longer lasting alternatives became available in the 1950s in the form of fluorescent tubes. These led to compact fluorescent lamps that screw into a regular light bulb socket, widely marketed today as low energy light bulbs. But, as anyone spending long hours working under the glare of poor fluorescent light in the modern office will testify, the quality of this lighting is a far cry from the warmth of natural daylight.

The latest breakthrough in the search for the holy grail of a cheap, pure white-light LED has been revealed in the journal Nature. After previously developing colour LEDs for mobile phone screens, a team of researchers at Princeton University and the University of Southern California now believe it is on track for designing an efficient white-light LED suitable for mass production.

The researchers initially combined phosphorescent red, green and blue wavelength LEDs to generate white LED light, in a project funded by the U.S. Department of Energy. However, they encountered problems with rapid burnout of the blue component. By replacing the blue phosphorescence with a fluorescent dye, the researchers found that they got a long lasting, high quality white LED, which was 20 percent more efficient than their triple phosphorescent LED. It was also up to 75 percent more efficient than conventional incandescent light bulbs of similar brightness. The researchers hope that with further refinement, their device will be at least three times more efficient than an incandescent light bulb.

In the study, the scientists used a special type of LED known as an organic LED (OLED), which has an organic carbon compound for its emitting layer. As OLEDs are lighter, thinner and more flexible than conventional LEDs, and are transparent when turned off, they can be incorporated into almost any flat or curved surface. With the possibility of having whole walls, furniture and even windows in the home as large sheets of LEDs lighting, adjustable for colour and temperature, interior design could be set for a major transformation in the near future.
/ENDS