Sandia National Labs’ effort to make a better LED aims at a brighter, more efficient world

Sandia labs wants to improve the world’s lighting

ALBUQUERQUE, N.M. — Sandia National Laboratories scientist Jerry Simmons envisions a future of brighter, more efficient lights, with people even being able to tune the color of light in a room to suit a mood or the time of day.

What he has in mind is definitely not Thomas Edison’s light bulb.

It isn’t even a bulb in the sense of incandescent bulbs, the newer twisty compact fluorescent lighting bulbs or the fluorescent tubes that light offices.

What Sandia is working toward is a better light bulb using LEDs — light emitting diodes — such as those that power flashlights and traffic lights.

The payoff could be huge.

About 22 percent of U.S. electrical use goes for lighting, but much of that energy is wasted.

Fluorescent lights are only about 20 percent efficient. Even that’s four times better than the 5 percent efficiency of incandescent bulbs.

E. Fred Schubert, Wellfleet senior constellation professor at Rensselaer Polytechnic Institute in Troy, N.Y., who works in the LED field, said no one talked much about solid state lighting until Sandia brought it to the forefront about a decade ago.

The lab, he said, is making tremendous progress in the lighting field.

“Our homes still have conventional light sources but the work at Sandia National Laboratories and industry as well and at universities — that will change the world,” said Schubert, who predicts LEDs someday will wipe out conventional lighting.

Not only can they save electricity, they have an environmental advantage since they don’t need the mercury that’s inside CFLs, he said.

In addition, solid state lighting has potential new functions — making possible, for example, the countdown in modern traffic crossing lights that tell pedestrians how many seconds are left to walk across a street, he said.

“This is just the beginning,” Schubert said.

LEDs don’t have a filament that will burn out. Rather, they’re illuminated by the movement of electrons in a semiconductor — a material that can conduct electrical current — and they’re grown on a wafer like a computer chip.

But there are large scientific challenges since semiconductors have defects that hurt their ability to conduct current, said Jeffrey Tsao, chief scientist for Sandia’s new Energy Frontier Research Center.

Researchers are looking at LEDs at three levels: the basic science underlying technical challenges; applied technology, or how to use the science to make lights more efficient; and how to manufacture a product so it’s affordable.

Simmons said some types of LEDs coming on the market are more efficient than fluorescents but not as efficient as what Sandia wants.

Sandia’s center is growing LEDs and using various ways to look at materials’ structure to understand the physics and how to extract light at different wavelengths and bleed off heat that hurts efficiency.

Simmons said the project’s 25 researchers are looking at the efficiency of getting light out of the chip.

White light is made up of all the colors in the visible spectrum, so the color of light can be changed by how much power goes into what part of the spectrum. That determines how yellow or blue light is, said Simmons, lead scientist on the project.

It’s hard to create all light equally, however. Each color has a different wavelength, and efficiency varies with the wavelength.

If the entire visible spectrum is present, it’s easy to see the richness of a green bowl full of luscious blueberries and glistening strawberries. Producing only part of the visual light makes the fruit look sickly — similar to trying to determine the color of a car under orange sodium vapor lights in parking lots.

“It’s kind of like putting light underwater in a pond. A lot of light stays underwater and never gets out,” Simmons said.

One challenge is increasing the efficiency of green — and to a lesser extent — orange light, both of which can’t be produced as easily as say, blue light.

Tsao said only when scientists can extract light from all colors of the spectrum efficiently will scientists be able to make LEDs compete with fluorescent and incandescent lights.