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Published: Tuesday, 4/3/2001

Diodes offer lighting a brighter idea, scientists say

BY MICHAEL WOODS
BLADE SCIENCE EDITOR

SAN DIEGO - A revolution in lighting technology, unparalleled since Thomas Alva Edison introduced the light bulb almost 125 years ago, quietly has begun, scientists said here.

Spell it LED for light-emitting diode, which researchers described as the light source of the 21st century.

“Advances in LED lighting are occurring at a breath-taking rate,” Dr. Arthur Ellis, of the University of Wisconsin-Madison, told a national meeting of the American Chemical Society. “We're really in the midst of a revolution, and that's no exaggeration.”

Advances in technology have poised the once small, dim device to make a great leap forward and replace many conventional sources of light, said Dr. Stephen Stockman.

Uses of light-emitting diodes have expanded beyond their familiar role as those tiny “indicator” lights and numeric displays on consumer electronic devices and appliances.

“Although the public may not be aware, we're in the midst right now of developing a whole new industry that will light the world in the years ahead,” he said.

The diodes are solid-state devices like computer chips, made from special semiconductor materials that convert electricity directly into light. They do not use the glowing filaments in incandescent bulbs, or the technology of fluorescent lights. Small and durable, the light-emitting diodes consume less electricity, last longer, and have other advantages.

Dr. Stockman, who is with a diode firm called LumiLeds Lighting, in San Jose, California, described how discoveries in chemistry have produced improved materials for making the device.

“These new semiconductor materials are responsible for a dramatic improvement in the brightness of light from LEDs,” he explained. “The advances have been impressive, especially when you consider that there has been essentially no improvement in brightness of the incandescent light bulb since Edison's day.”

Among other key advances are development of a long-sought light-emitting diode that produces pure white light, and an improved generation of LEPs, or light-emitting polymers, which are organic semiconducting materials, compared to the inorganic semiconductors used in light-emitting diodes.

Both generate light in similar ways. But light from the polymers can be patterned like liquid crystal displays. The polymers can be fabricated into very thin and flexible arrays.

Light-emitting diodes have replaced conventional bulbs for some uses, Dr. Stockman said.

Thousands of communities, for instance, are using the diodes for traffic signals. The devices mean traffic signals that weigh less, last longer, and consume 90 per cent less electricity.

Dr. Stockman said a diode traffic signal typically pays for itself in power savings within one year. Some have cut electric bills by hundreds of thousands of dollars annually with light-emitting diode signals.

The automobile industry is embracing the diodes in brake lights, turn signal lights, behind-the-dash lighting for the instrument cluster, and other applications. One manufacturer uses almost 300 of the diodes in each of its cars, he said.

Light-emitting diodes are replacing conventional lighting in large, full-color video advertising screens and scoreboards.

One LED flashlight manufacturer claims its batteries will last for 336 hours of continuous use, compared to 5 to 10 hours for a regular flashlight. The diode's life - 100,000 hours.

What's on the horizon for light-emitting diodes?

Scientists described new uses in strip lights for path marking and landscaping; hazard markers imbedded in floors and steps; highway lane markers that remain highly visible in rain and fog; and interior room lighting, including walls covered with diodes that emit a soft glow.

Major lighting manufacturers see the handwriting on the wall, scientists said, and are teaming up with diode makers. General Electric Lighting, for instance, is working with diode-maker Emcore in a new lighting division called GELCore, based in Independence, Ohio.



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