January 12, 2009 By Elaine Rundle
Anchorage, Alaska, sought a way to make its 16,500 streetlights more energy efficient. What the city found was plan to replace current streetlights -- or high-pressure sodium (HPS) lamps -- with light-emitting diodes (LEDs) that are connected to a centralized control system.
On Aug. 12, 2008, Anchorage spent $2.2 million on 4,300 LEDs to retrofit its streetlights, according to Michael Barber, the city's lighting program manager. Currently 1,200 of the LEDs have been installed, and the city hopes to have the remaining 3,100 in place by May. Barber said by May the city also hopes to have completed the next round of budgets, so it can work toward its goal of retrofitting all of the streetlights.
Barber said the No. 1 reason for the streetlight retrofit was to save money through energy efficiency. He reported that retrofitted streetlights used 50 percent to 60 percent less energy than the HPS lamps.
The LEDs are connected to a centralized control system. "There's a platform, a map and GPS locations of all the lights, and we're getting data sent to that central location about lights all over the city," Barber said. He later added, "Either over a power line or radio frequency, we've got a light that's communicating with a server and telling it, 'I'm burning at this temperature.' Or, 'For some reason I'm sucking up way more energy than I should.'"
Before the centralized system, city staff or residents had to physically see and report a burned out streetlight. Now the city knows immediately when a light needs to be replaced or if it's having problems. However, one of the benefits of LEDs is their long life span. Although Barber said LEDs cost $500 to $1,000 each, they last about five times longer than the HPS bulbs -- or up to 10 years.
The system allows for streetlights to be controlled remotely, which according to Barber, can decrease energy consumption by up to an additional 20 percent. Anchorage plans to utilize this for curfew dimming in residential neighborhoods. For example, dimming streetlights by 40 to 50 percent between the hours of 10 p.m. and 5 a.m. would add to the energy and money saved.
Barber estimated that when the entire city's streetlights are converted to LEDs, Anchorage could see savings between $1.5 million and $1.7 million, and that's before adding the dimming-control techniques. "We don't know what that would mean if we also implemented controls over the whole city, but it wouldn't be shocking to see 70 percent energy efficiency over the HPS," he said.