Photo by Randy Montoya
They are white LEDs, full-spectrum versions of the colored light-emitting pinpoints commercialized in recent decades as ubiquitous indicator lights.
But if bigger, brighter white LEDs can be manufactured more economically, they could challenge the 100-year-old incandescent bulb in the multibillion-dollar lighting market. LEDs last for years, are tough and use less energy than conventional light bulbs.
Market research firm iSuppli Corp. projects the market for high-brightness LEDs will grow from $1.53 billion in 2003 to $2.85 billion in 2007.
According to Bob Steele, an analyst with Strategies Unlimited in Mountain View, Calif., the market for high-brightness LEDs grew 50 percent in 2002 and should match that in 2003. Two of the biggest current markets for bright LEDs, he said, are cell phone screens and automobile dashboards.
Some governments are making solid-state lighting a national priority. The U.S. Energy Department estimated in 2002 that solid-state lighting could cut the electricity used for illumination up to 50 percent by 2025, savings that could significantly reduce the associated carbon emissions from power plants.
The energy bill before Congress includes funding for the Next Generation Lighting Initiative, which calls for $50 million a year over 10 years to advance solid-state lighting.
In the meantime, the Energy Department is supporting research on how quantum dots could boost the performance of solid-state lighting devices and funding work on better ways to control the nanostructure of semiconducting materials in white LEDs.
The power of LEDs has almost doubled every two years over the last decade, but much improvement is still needed to make white LEDs viable in wider markets. They cost as much as 50 times more than conventional bulbs that sell for 40 cents apiece. And while LEDs are more energy efficient than incandescent bulbs, they aren’t yet as frugal as fluorescent tubes.
According to Tim Whitaker, editor of Compound Semiconductor, the industry is looking to improve the “cost per lumen” of LEDs by, among other things, developing lower-cost starting materials.
But for white LEDs to become more affordable for consumers, experts say, breakthroughs will be required in areas such as the precise layering of semiconducting materials like gallium nitride used in many white LEDs.
Some of the firms in the white-light hunt: LumiLeds Lighting LLC, a partnership between Agilent Technologies and Philips Lighting that produces the Audi’s trick running lights; OSRAM Opto Semiconductors, a subsidiary of the German lamp maker that supplied the devices that light up Jefferson’s monument.
In July 2003, Sandia National Laboratories announced that researchers had built the first devices that used encapsulated quantum dots, or nanocrystals, to produce white and blue LED light. Quantum dots can absorb one kind of light and emit another. The scientists employed an LED that emitted near-ultraviolet light. The quantum dots absorbed the ultraviolet light and then produced visible light controlled by the size and chemical surface of the quantum dots.
A mixture of quantum dots could be a good alternative to the yellow phosphors currently used to help blue LEDs produce relatively “white” light. The dots could emit a wider spectrum of light than a single phosphor material, and because of their size, are less likely to scatter an LED’s light output.
Evident Technologies in Troy, N.Y., is also working on solid-state lighting applications for its quantum dots. Marketing Director Steven Talbot noted that quantum dots with a range of precise optical properties could be incorporated into the epoxy lens atop an LED to shift the resulting light to a warmer and fuller white light. He added that an LED-type device could be built entirely on quantum dots rather than bulk semiconductor materials because quantum dots glow when stimulated electrically.
Nadarajah Narendran, director of research at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, said that his group is identifying applications that can significantly benefit from LED technology — for example, how white LEDs could light refrigerator cases in supermarkets more efficiently.
Another intriguing possibility for LEDs, said Narendran, is for more flexible lighting. Unlike the static light fixtures we presently have, homes and offices could be illuminated with systems that can produce different shades of white light depending on the time of day or preferences. Auto manufacturers are already looking to develop advanced headlights using LEDs, and electronic control systems that can change the headlight beam and direction.