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.
Northern Lights
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]."
Extreme Lighting Makeover
Centralized control systems are also benefiting cities that haven't converted to LED streetlights. About five years ago,Los Angeles began testing a remote-monitoring system on 5,000 of its more than 209,000 streetlights, according to Norma Isahakian, assistant director of the city's Bureau of Street Lighting.
"I think the main benefit up to this point has been reporting on when the lights are out," Isahakian said. "We want to make sure the majority of lights are on, not just for the fact that we want the lights on, but there are also liability reasons."
The city is attaching external computer boxes to its streetlights. Isahakian said the external units work best because Los Angeles uses more than one streetlight manufacturer. There's the cost of an external unit for each light and the base computer unit that information is transmitted to. "They use radio waves to get the information back to the main unit, and the main unit uses a cellular system to get it back to the main office," she explained.
She said the project was initially launched in a convenient location where city-employed field workers were close enough to physically see the lights, which they then tracked online. The computer boxes are now installed on new streetlights in construction areas and on those that are replaced.
Better workflow has been another improvement. "A lot of times when we go out to the unit, we know what's going wrong with it," Isahakian said. "Instead of making multiple trips, we'll make only one trip because we'll know the unit just needs to be changed."
Los Angeles is also beginning to pilot the use of LED streetlights. According to the city's LED Street Lighting Energy Efficiency Program, the first phase involved retrofitting 100 streetlights between November 2008 and January 2009. According to a document from the program, "Based on preliminary analysis and evaluation of the development of the LED industry, the bureau is strongly considering a large-scale project to replace existing roadway fixtures into LED or any other high-efficiency light source."
Isahakian said the bureau has been researching LEDs for the last couple of years, but only recently did the lights begin performing up to the standard it was looking for. "I think the remote-monitoring system and the LED fixtures together are really going to make more sense," she said, "because you're able to do more things with them, like dim the streetlights."
