A fact sheet from Brodrick’s office says this about LEDs: “In the coming decade, they will become a key to affordable net-zero energy buildings, buildings that produce at least as much energy annually as they use from the grid.”

The technology is advancing quickly, and costs will continue to drop, Brodrick said. The DOE tests LEDs and sets performance and efficiency guidelines under its Energy Star program.

LEDs are directional lights, used in recessed lighting and under-counter lights, for example. They’re not yet available as bulbs that cast light all around and fit in ordinary sockets.

“There’s an enormous and exciting potential, but we have a long way to go before we see anything besides directional lighting,” said Jeffrey P. Harris, the vice president for programs at the Alliance to Save Energy, a nonprofit group that promotes energy efficiency.

Even so, LEDs already are used to light offices, hotels, restaurants and other businesses.

The DOE predicts that LEDs will have better performance capability than fluorescent lighting in the next few years, and that they’ll continue to improve after that. They’re now comparable with fluorescent fixtures in efficiency, and the DOE says its Energy Star LEDs last two to five times longer.

Cost is the biggest reason that LEDs aren’t used more widely, Brodrick said.

LEDs have other advantages: They can be dimmed, don’t emit heat, don’t contain mercury – unlike compact fluorescents – and can produce warm-toned light.

Home Depot, the world’s biggest retailer of light bulbs, is starting to stock LED bulbs this summer and plans to have 10 kinds by September, said Jorge Fernandez, who’s in charge of light bulb purchases for the company.

Philips is working on many kinds of LEDs, including one to replace a 40-watt incandescent bulb that’s scheduled to be available next year, she said.

Derrick Hall of RE/Construct Inc. in Asheville, N.C., said that residential customers weren’t asking for LEDs because of the high upfront cost. Still, he’s hearing of some nonresidential customers who are looking into LEDs for the energy savings.

LEDs are much better than other lighting options, Hall said. The quality of the light is “far superior,” they offer big energy savings and there’s no cost to society for dealing with mercury, he said. Mercury, a neurotoxin, is found in small amounts in compact fluorescent bulbs.