Quiet revolution may change way we light our world

Sandia joins revolution in solid-state lighting

NEW WHITE LIGHT — Sandia researcher Art Fischer holds a sapphire substrate with indium gallium nitride layers. This is the base material for semiconductor light-emitting diodes that emit green, blue, and near-ultraviolet light. (Photo by Randy Montoya) Download 300dpi JPEG image, ‘LEDpic2.jpg’, 592K (Media are welcome to download/publish this image with related news stories.)

Some 25 Sandia researchers are working on an project that will establish the fundamental science and technology base to replace the country’s primary lighting source, incandescent bulbs and fluorescent tubes, with semiconductor light-emitting diodes (LEDs) — solid state lighting.

Sandia Senior Scientist James Gee, together with department managers Jerry Simmons and Bob Biefeld, head up the project.

“In some ways the revolution in lighting can be compared to the revolution in electronics that began 50 years ago and is only now reaching maturity,” Gee says. “Just as for electronics, glass bulbs and vacuum tubes are giving way to semiconductors. And as in the microelectronics revolution, many of the possible applications for solid-state lighting will occur in ways that have not yet been envisioned.”

LEDs are already found in toys, electronics, traffic lights, automobile signals, and large outdoor displays — devices that require durability, compactness, and cool operation. In some applications they also enable significant cost savings due to their lower consumption of energy: LED-based red traffic lights, for example, consume one-tenth the energy of their incandescent counterparts, enabling them to pay for themselves in as little as one year.

As LED technology matures, revolution leaders expect solid-state lighting to also rapidly outdistance conventional lighting sources in both performance and cost.

“This new white light source could change the way we live, and the way we consume energy,” says Simmons, who manages the project. “LEDs could be 10 times more efficient than incandescent bulbs and two times more efficient than fluorescents. Clearly, LEDs’ replacement of conventional light sources would significantly reduce worldwide energy consumption.”

Lighting is presently responsible for roughly 20 percent of electricity consumption. Researchers believe that the development and adoption of solid state lighting technology could reduce the nation’s electrical consumption by 10 percent.

LEDs were first demonstrated in 1962 by General Electric. The first products were introduced in 1968 — indicator lamps by Monsanto and an electronic display by Hewlett-Packard. However, LEDs were limited to small-signal applications until 1985 when LED power was increased, resulting in new applications. In 1993 researchers at several universities in the US and Japan developed a fairly efficient blue light LED based on gallium nitride. Efficiency improvements followed quickly. Today, energy-efficient LEDs are available from red to green to blue light, making it possible to generate white light for illumination.

NEW SUBSTRATE — Sandia researchers James Gee and Jerry Simmons examine an image of light emission from an indium gallium nitride LED on the new type of substrate that was developed at and patented at Sandia. The new substrate features reduced defect densities by growing suspended wings, “cantilevers,” of the semiconductor over an etched trench. (Photo by Randy Montoya) Download 300dpi JPEG image, ‘LED2pic2.jpg’, 2MB (Media are welcome to download/publish this image with related news stories.)

However, Gee says, LED-based light sources are expensive — more than two orders of magnitude more expensive than commercial incandescent light bulbs — and will not be practical until their costs are reduced and efficiency is further increased.

As part of the LEDsproject, some 25 Sandia researchers are exploring ways to do exactly that — make LEDs more efficient and less costly. They are working on the fundamental science and technology challenges where Sandia has unique capabilities. Among those challenges are:

• Developing an improved understanding of the physics of the gallium nitride-based materials that are the base materials of the LEDs.
• Improving optoelectronic devices and materials for abundant photon generation and high light extraction efficiency.
• Improving wavelength conversion and color mixing technologies for generation of white light.
• Improving packaging technologies for high-power LEDs.

Numerous industrial companies, as well as universities, are working to develop technologies for solid state lighting. However, Biefeld says, “in many respects Sandia is unique, due to our extensive capabilities in semiconductor growth and processing, reactor modeling, and experimental and theoretical materials physics, all located at a single institution.”

“These are exciting challenges that will engage our scientists over the next several years,” Gee says. “Our work will position Sandia to become a leading developer of the science and technology for this revolution in lighting.”