An "adaptive lighting" concept is now being tested in San Jose, Calif., in the heart of Silicon Valley. In this test, streets can be made brighter, darker or even be illuminated with flashing strobes upon command.

In one of the biggest urban tests of the science so far in the U.S., 125 LED streetlamps will be installed in the city, aiming at cutting down on energy consumption and lowering the utility costs of the city by employing the flexibility of LED technology.

Under push by federal and state agencies to modernize the nation's lighting infrastructure, cities are now faced with tighter budgets and are looking for ways to cut street-lighting costs and to reduce emissions from power plants.

Unlike traditional streetlamps, LED lights can be programmed to respond to specific commands. For example, a city could dim the lighting on commercial strips after business hours, or turn up the lights after bars close, says Jim Helmer, director of San Jose's transportation department. The city hopes to cut down on "light spillage" -- city planners' term for light that shines where it isn't wanted, creating an urban nuisance. The lights will be controlled under a system developed by energy-software company Echelon Corp. of San Jose, the general contractor in the pilot program.

The city plans to spend $150,000 to $200,000 on a pilot project in its Hillview North neighborhood, and it is seeking an additional $2 million in federal stimulus funds to enlarge the test.

The installation of LED streetlights in San Jose could cut energy consumption by 10% to 60%, depending on the brightness of the lights. The white LEDs will have a range of between one and 82 watts and will replace 55-watt, yellowish sodium-vapor lamps.

However, many cities see little financial advantage to switching their lighting systems for the time being.

A single LED streetlight can cost $600 to install, compared with $200 for a sodium-vapor lamp. What's more, utilities often charge cities a flat rate based on the number of streetlamps they operate, regardless of use.

Some of the lighting tests are funded by the DOE, such as a recent retrofit of a Raley's supermarket parking lot in West Sacramento, Calif. The 16 LED lamps with motion sensors run at 49 watts, and power up to 149 watts when sensing activity. They could pay for themselves in energy savings in four to five years.

On Mount Hamilton, which is fourteen miles east of San Jose, the astronomers at the Lick Observatory have another concern: the bright white light of LEDs illuminate the night sky and obscure views of planets and stars. And scientists are working with city officials to make LEDs benign, suggesting they dim after midnight or eliminate near-infrared and ultraviolet light from the LED color spectrum.