Spurred by a desire to lower energy costs, cities and towns in the area — and throughout the country — are overhauling their street lights. One after another, high-pressure sodium lights, a longtime industry standard, are being replaced with brighter, more efficient LEDs.
“Within the state, in general, it’s really picked up in the last few years,” said Patrick Roche, energy coordinator at the Metropolitan Area Planning Council, which has worked with dozens of communities around Boston to convert their lights.
But specialists warn that the “blue light” from some LEDs can disrupt the body’s production of melatonin, a hormone that influences sleep, if exposed to it at night.
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In June, the American Medical Association released a statement urging communities not to install bright LEDs with high levels of blue light, warning of effects such as reduced sleep time, low-quality sleep, and even obesity.
The statement also contained words of caution for drivers.
“Discomfort and disability from intense, blue-rich LED lighting can decrease visual acuity and safety,” it said, “resulting in concerns and creating a road hazard.”
Roche pointed out that screens on smartphones and computers also release blue light.
“We’re exposed to much more blue light from those devices than a few minutes we spend walking around outside,” he said.
Yet it is the impact that LED streetlights could have on wildlife that most concerns some activists.
James Karl Fischer, executive director of the Zoological Lighting Institute, a nonprofit that supports research on how light affects wildlife, says that blue light can disrupt the nocturnal habits of some animals. Other animals are attracted to objects that emit blue light, which could cause birds, for example, to be thrown off their migration patterns, he said.
“That’s a huge issue,” Fischer said, “because if they’re expending energy to come into these areas that they don’t normally go into, and they spend time there, they don’t have the same kind of energy and fat reserves that they would have normally to push on with their migrations.”
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Kelly Beatty, who is on the board of directors of the same anti-light pollution group as Fischer, supports the conversion to LED streetlights, so long as the municipalities follow certain guidelines.
“Pick LEDs that have the lowest color temperature possible” is Beatty’s suggestion to those in charge of the decisions. He says a lower color temperature, measured on the Kelvin scale, tends to mean less blue light. He recommended lights with a color temperature of 3,000K or less. Their color is closer to yellow and orange, while LEDs with higher color temperatures give out a more white and blue light.
Fischer, though, said that while lower color temperature lights are a start in the right direction, some 3,000K LEDs could still have a high percentage of blue light.
What communities should do instead, he said, is reduce overall lighting.
“The best lighting environment is always a natural one, for animals,” he said.
Municipalities south of Boston that have completed street light retrofit programs in recent years include Dedham, Easton, Randolph, Sharon, and Westwood, according to Roche. Other communities, like Brockton and Cohasset, are exploring the issue or are in the process of replacing their street lights.
Roche said the cost of LED fixtures has fallen, making it more feasible for communities to make the change. An additional incentive is that LEDs don’t need to be replaced as often, with some expected to last more than 20 years. High-pressure sodium lights, which Tom Philbin, Westwood’s energy manager, says has been the standard since the late ‘80s and early ‘90s, can last as few as five to seven years.
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“It’s a great low-hanging fruit energy savings,” Roche said.
Westwood has retrofitted more than 1,400 street lights with LEDs measuring 4,000K. Philbin said the town tried out LEDs of varying temperatures. Residents preferred those that were 4,000K, he said; the 5,000K LEDs, with their white light, were irritating, and residents felt the 3,000K LEDs were not bright enough for the streets.
Philbin said that, from his understanding, blue light wouldn’t be an issue at 4,000K. And he hasn’t heard of any complaints in town about blue light, or the new street lights, at all. In fact, he said, the program has been a hit.
“The people have all said it makes the street brighter,” he said. “We’re getting requests for street lights where we didn’t have any.”
And the town is saving money, too -- about $4,000 a month in energy costs, Philbin said. He estimated that within the next two or three years, the savings will have covered the town’s contribution to the project.
Easton has also seen big savings since it began replacing its high-pressure sodium lights with 4,000K LEDs in 2013.
David Field, who heads Easton’s public works department, said the town is saving more than $57,000 annually on energy costs. He said that while researching LEDs, concerns came up about glare, but not about blue light.
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And he said that Easton residents have given positive feedback about the new street lights.
“The number one comment we got was, ‘When are they going to put them on my street?’” Field said.
Jacob Carozza can be reached at jacob.carozza@globe.com. Follow him on Twitter @jacobcarozza.