Unlike regular incandescent bulbs, LEDs emit light without a wire filament, so they take longer to burn out, and they produce less heat.
But semiconductors have long been too expensive for use in a broad range of commercial applications. Until the 1990s LEDs were primarily used only as indicator lights, such as those in power buttons on electronic gadgets.
Today the costs of semiconductors are dropping by about half each year, according to DenBaars.
Craford, of Philips Lumileds, said that advances in the materials and designs used to make LEDs have also led to dramatic improvements in how light is generated and extracted.
While no single breakthrough stands out, Craford said, the cumulative advances translate to higher production and output.
"We are generating more light inside the [semiconductor] chip and we are getting more of what we generate out, and that makes the total output substantially higher," he said.
UCSB's DenBaars said that increasingly complex structures drawn on the semiconductor chips themselves have led to the improved light extraction efficiency.
It's "literally like drawing lenses on the chip," he said.
"Holy Grail" of Lighting
Within the last decade colored LEDs have been widely adopted for uses such as exit signs, traffic lights, and automobile taillights, Craford noted.
The U.S. Department of Energy reported in 2003 that these types of niche applications already save the country 9.6 terawatt hours a year of electricity.
Perhaps the biggest remaining challenge is to create efficient and economical white-light LEDs, Craford said.
LEDs by their nature give off distinct colors—one type of material glows green while another glows blue. But white is a combination of colors, Craford explained.
To make white light with an LED, scientists most commonly add a yellowish phosphorescent chemical to a blue-emitting diode. The combination of yellow and blue gives an appearance of white to the human eye.
(Related news: "Accidental Find to Signal 'Lights Out' for Incandescent Bulbs?" [November 1, 2005].)
Advances in phosphor technology have already given white LEDs traction in the marketplace, especially in flashlights, according to Craford.
And he believes that as the technological advances continue, white LEDs "will replace conventional lighting for most general illumination purposes.
"I happen to believe it will replace virtually everything," he added.
A complete switch from modern light bulbs, though, could still be decades distant, he noted. Currently the best LEDs are about as efficient as compact fluorescent light bulbs.
These bulbs are five times more energy efficient than incandescent bulbs and are a much cheaper option than LEDs.
Noah Horowitz is a senior scientist with the nonprofit Natural Resources Defense Council in California.
He said through a spokesperson that LEDs that are more efficient than compact fluorescent bulbs are the "holy grail" of lighting, and the environmental group is optimistic about the use of LED technology in the future.
But today, he said, "they cost a lot and are not yet widely available for consumer applications."
Horowitz added that obtaining white light from LEDs that resembles the light of an incandescent remains a challenge, as does spreading the light out from the LED.
Currently, Horowitz said, LEDs are good at providing directional lighting, such as in a spotlight, but not as good for practical uses in things such as table lamps.
Philips Lumileds' Craford is confident that these improvements are coming and will soon make LEDs the light source of choice.
"LEDs are going to be a substantial part of the lighting in the upcoming years," he said, "and it's beginning to happen right now."
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