March 23, 2009 By Elaine Rundle
State and local governments looking to improve efficiency and cut costs are casting their gaze skyward -- at streetlights -- for an answer. Some cities are modernizing their streetlights with light-emitting diodes (LEDs), others link them to centralized control systems and some do a combination of both.
Replacing the high-pressure sodium (HPS) bulbs commonly used in streetlights with LEDs is a simple solution that can yield big benefits. According to a report from the Rensselaer Polytechnic Institute, Transcending the Replacement Paradigm of Solid-State Lighting, by Jong Kyu Kim and E. Fred Schubert, "Deployed on a large scale, LEDs have the potential to tremendously reduce pollution, save energy, save financial resources, and add new and unprecedented functionalities to photonic devices."
Another strategy used by some municipalities is implementing a centralized control system that alerts officials when a light goes out. Previously a city worker or resident had to see a malfunctioning light and report it. A centralized system allows manpower to be used more efficiently and helps track energy consumption.
Anchorage, Alaska, is lighting up the northern sky as the city works toward converting all its 16,500 streetlights to LEDs.
According to Michael Barber, the city's lighting program manager, Anchorage purchased 4,300 LEDS in August 2008 for $2.2 million. He said energy efficiency and cost savings drove the initiative. So far, 1,200 lights have been installed, and Barber said the remaining 3,100 of them would likely be set up by May 2009.
One of LEDs' main benefits -- besides using 50 percent less energy than traditional bulbs -- is that they can be connected to a centralized control system, which Anchorage has done. "Either over the power line or radio frequency, we' have 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,'" Barber said.
The system lets the city know in real time when a light should be replaced or needs warranty support. That's important because LED bulbs are significantly more expensive. In the past, when HPS streetlight bulb failed within the warranty period, Barber said the city would forgo the warranty and just replace it because those bulbs are cheap -- only $10 each. LEDs, however, cost $500 to $1,000 apiece, so it's important to have accurate information. When and LED it loses 30 percent of its initial luminosity, it's considered to have failed.
"With control systems we can have the light tell us when there's a warranty issue or if the light goes out," he said. "We'll see a surge and a change in the energy consumption on that circuit."
Another benefit of the centralized system is increased efficiency through the use of controls, which leads to more energy and money saved. LEDs have dimmable ballasts that allow officials to change the light's brightness, which is a big advantage over HPS bulbs. Barber said the city is planning to dim the streetlights in residential neighborhoods between 10 p.m. and 5 a.m. by 40 to 50 percent.
He hoped that by May 2009, the city's next round of budgets would be completed and there would be funding to continue retrofitting the remaining 12,200 streetlights.
"We estimate that when we do the whole city, it will be within $1.5 [million] and $1.7 million a year in savings," Barber said. "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 efficiency over the [HPS]."
Centralized control systems are also benefiting cities that haven't converted to LED streetlights. About five years ago,
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