How many Ann Arbor city workers does it take to screw in a light bulb?

Soon, none.

Instead, they will be installing light-emitting diodes, or LEDs, to replace about 1,400 street lights.

The eco-friendly city about 30 miles west of Detroit says it will be the nation's first to convert all downtown street lights to LED technology, which uses less than half the energy of traditional bulbs and could save the community $100,000 a year.

"LEDs pay for themselves in four years," said Mayor John Hieftje, who announced the city's plans this week as it joined Raleigh, N.C., and Toronto in the LED City initiative, an industry-government group working to evaluate, deploy and promote LED lighting.

"They provide the same light, but they last 10 years. We had to replace the old ones every two years."

LEDs, small chips usually encased in a glass dome the size of a matchstick head, have been used in electronics for decades.

They usually gave off red or green light, but a scientific breakthrough in the 1990s paved the way for LEDs that produce white light.

Lighting consumes 22 percent of the electricity produced in the United States, according to the U.S. Department of Energy, and widespread use of LED technology could cut consumption in half.

Hieftje said Ann Arbor's lighting conversion will reduce the city's production of carbon dioxide and gases that contribute to global warming in an amount equal to taking 400 cars off the road.

The two-year project is being funded by a $630,000 grant from the city's Downtown Development Authority.

Greg Merritt, director of corporate marketing at Durham, N.C.-based Cree Inc., which is making the components inside Ann Arbor's new lights, acknowledged LEDs can be costly.

But "as we improve the technology, the economics make sense for more and more applications," he said.