April 22, 2009 By Elaine Rundle
San Jose, Calif., is embarking on its second pilot project of converting streetlights to utilize light-emitting diodes (LEDs), which can be networked and have a longer lifespan than traditional streetlight bulbs. The city will retrofit 125 of its 65,000 streetlights by June.
According to Jim Helmer, director of the city's Department of Transportation, the main drivers behind the project are contributing to the urban forestry program, which means adding more trees to sidewalks while ensuring that light penetrates through the trees down to the street; providing white light versus the yellow light the current streetlights emit; reducing maintenance by having increased bulb life expectancy; and increasing energy savings.
Helmer said the city was looking for new streetlights that had GPS in the heads so that they would know their location. "No matter where that light gets installed, the light would understand where it is, and it would memorize the sunrise and sunset patterns for that area," he said. "It would have that built into its programmable memory."
This allows engineers to program the light to give 50 percent output for the first hour of sunset, then burn at 100 percent when it's pitch dark and at sunrise begin lowering the output. Helmer said traditional streetlights burn full strength as soon as their photo eyes alert them to turn on, which could be as soon as the sun begins to set but too early to require 100 percent output.
The LED streetlights will be connected through the electrical wires that feed electricity to the lights. The power lines will carry the communication signal and allow engineers to control the lights from a remote location. The network also will provide real-time updates on the lights' statuses, which lets maintenance workers know immediately when a light is out.
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