LEDs hit the streets

June 3, 2011
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Boston’s most wasteful streetlights are being systematically replaced by ultra-efficient light-emitting diodes (LEDs)—casting a new light on neighborhoods across the city, including Mission Hill.

About 18,000 of the 68,000 streetlights in the city are powered by mercury vapor, the least energy-efficient technology in common use, said Bryan Glascock, head of the city’s Environment Department. Glascock and city Street Lighting Manager Glenn Cooper presented the new lights at the April 26 meeting of the Jamaica Plain Neighborhood Council.

The city is currently in the process of replacing all of them with LEDs—which are 60 percent more efficient than mercury vapor fixtures. The work is already completed on the about 100 mercury vapor lights on the Hill, and should be done citywide by the end of the calendar year, Cooper said at the meeting.

The replacement project is expected to be a major contributor to a $1.4 million reduction in the budget for city’s streetlights and signals program in the coming year, according to city budget documents. The city plans to spend $14.7 million on streetlight and signals in Fiscal Year 2012, which begins July 1.

The new lights are made up of clusters of 40 small LED lights that can be individually adjusted to evenly illuminate the street.

Because of rebates offered by utility companies, and steep reductions in the cost of LED technology in recent months, the city is essentially getting the lights for free, Glascock said. The city is only paying for the cost of installation, and the new lights will pay for themselves in energy cost savings in a few years, Glascock said.

“It was financially advantageous for the city to go whole hog,” he said.

Mercury vapor lights give of a “white-ish, blue-ish light” Glascock said. They have mostly been used on residential streets. The orange streetlights that illuminate city commercial districts are powered by sodium vapor. Those lights—which are more efficient and less costly than mercury vapor—are not currently not scheduled to be replaced, he said, but the city would likely take another look at replacing them if the cost of LED lighting continues to go down.

Another reason for replacing the mercury vapor lights is they are becoming obsolete and manufacturers are starting to phase out production of their bulbs, he said.

The new lights are “slightly dimmer” than the ones they are replacing, Glascock said at the meeting.

JPNC member David Baron asked if that could pose a public safety hazard.

But Glascock said the light they produce a “clearer” light than the mercury vapor bulbs. “Your eyes appreciate colors and shapes better” when they are illuminated by the LEDs, he said.

The clusters of 40 small, individually positioned LEDs also mean that the light they give off can be specifically trained to “produce an even lighting system down the street,” said Cooper.

By contrast, mercury vapor and sodium vapor lights create “light wells,” Cooper said. They emit a strong direct light beneath the poles, but rapidly dim on the edges, leaving spaces between the lights that are un-illuminated.

The new fixtures are also “dark sky compliant,” meaning that, unlike older lights, they do not shine into the sky at all, Cooper said. He demonstrated that feature of the new lights by plugging one he had brought with him into a wall socket at the meeting. When the light was dimmed in the room, Cooper’s lower body was illuminated by the LED fixture, but his upper body and face remained unlit.

Advocates for dark sky compliant street lighting say that the “light pollution” given off by streetlights that shine upward is a waste of energy; that it makes it harder to see stars and planets in urban areas at night; and that it is harmful to nocturnal animals.

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