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To: Jack Hartmann who wrote (4072)	10/28/2000 8:44:29 AM
From: Jack Hartmann	Read Replies (1) \| Respond to of 10714

A Laser in Your Lightbulb? Tiny, energy-efficient devices may one day replace Edison's bulb -- and cut energy costs by $100 billion a year Light-emitting diodes (LEDs) that glow red have already replaced the bulbs in traffic lights and automobile taillights. Other types of LEDs emit green light and blue light. But until recently, no one had found a practical way to coax a solid-state device into producing the familiar white light that we favor to illuminate homes, offices, and factories. The answer may be arrays of tiny lasers developed by a team of researchers from Brown University in Providence and Sandia National Laboratories in Albuquerque. These scientists discovered a way to create a class of microlasers known as vertical-cavity surface-emitting lasers (VCSELS) that produce ultraviolet radiation. It's ultraviolet light that causes the phosphors on the inside of gas-filled fluorescent lights to glow white. The researchers believe that the same coatings will turn arrays of tiny lasers into practical lamps. "Many groups are racing to create such lasers in the UV range," says Jung Han, who heads the Sandia group. "It was a dream. Now we have achieved it." Indeed, these solid-state emitters -- so small that several hundred can fit on a postage-stamp-size chip -- will last 5 to 10 times longer than fluorescent tubes and be far more durable. Moreover, they promise to change the way interior space is lighted. Instead of clunky fixtures, flat arrays could be arranged in any pattern, mounted on walls, ceilings, or even furniture. AIR CLEANER. The biggest payoff is likely to be in saved energy. Last year, researchers from Sandia and Hewlett-Packard Co. predicted that solid-state lighting applications would chop energy costs by $100 billion annually by 2025. Demand for electricity would be reduced by 120 gigawatts, resulting in carbon-emission reductions of 350 million tons a year. "No other major electricity application represents such a large energy savings potential," they concluded in a presentation at a meeting of the Optoelectronics Industry Development Assn. Other approaches are also vying for the huge lighting market. Blue LEDs, for example, can be combined with phosphors to create white light. One problem: The light is harsh and cold because it's overbalanced toward the blue spectrum. Arrays that combine the spectral ranges of red, blue, and green LEDs can also produce white light but are difficult and costly to fabricate. The Brown and Sandia researchers believe VCSELs have the brightest future because they create a monochromatic and directional beam. But even though the project has already been under way for several years, it still has a long way to go before a practical lamp can be demonstrated. The VCSEL laser itself was invented at Sandia 14 years ago when researchers showed they could use the techniques of semiconductor production to build a sandwich of nanometer-thick layers of highly reflective crystalline materials that performed in the same way as a conventional single-crystal laser. NEEDS HOUSEHOLD CURRENT. By manipulating the materials in the layers and their thickness, the scientific teams achieved the first ultraviolet VCSEL and published their initial results in the Oct. 12 issue of the journal Electronics Letters. A practical demonstration will require improving efficiency and finding ways to power the lasers with household current. Even if the VCSELs move rapidly to commercialization, "it's probably in the 5- to 10-year time frame," says Robert M. Biefeld, one of the Sandia researchers. The white-lighting developers hope to pick up the pace -- with a little help from the government. Sandia and OIDA are hosting a joint technical conference this month in Albuquerque. The agenda will be to reach a consensus on the major commercial and military applications of solid-state lighting and identify the technology needed to realize them. That, they hope, will become the grist for a national initiative to speed development and secure the U.S. a competitive position in a vast new market. Alan Hall in New York Edited by Douglas Harbrecht businessweek.com Interesting projection on the energy savings Jack