Walk down a Philadelphia street at night and most likely, you will find the city lit in a warm yellow glow. The familiar cast comes from high-pressure sodium lights — the conventional breed of streetlamp common in the city. But soon, those yellow nights will be a memory. Instead, Philadelphia will take on a whitish cast as the city’s Streets Department moves forward with a long-anticipated plan to replace its old bulbs with more energy efficient LEDs.
But as the city moves forward with the lighting makeover, experts are urging officials to consider public health and environmental questions raised by a 2016 study by the American Medical Association of the impact of LED lights.
The AMA's report found that high-intensity LED lights can emit a large enough amount of blue light — it appears white to the naked eye — to potentially pose health risks to humans, animals, birds, and insects. The excessive blue light messes with the inner biological clock that prepares organisms for the fluctuations of the day. The AMA argued that blue-rich LED streetlights could suppress melatonin, the hormone that regulates sleep, and could impact circadian sleep rhythms five times more than conventional street lamps.
“Large cities have been converting to LEDs for energy saving reasons, which is a really good idea,” said architect Helena van Vliet, president of BioPhilly, a local organization of architects and designers. “But we’ve discovered that a lot of the 4000 Kelvin [base unit of thermodynamic temperature] LEDs are uncomfortable for humans.”
There is no consensus on the AMA findings. The Department of Energy, academics and lighting professional and manufacturers associations have argued that there is a lack of sufficient evidence of the impacts of LED streetlights. But that hasn’t vanquished the concerns of Van Vliet and others who gathered for a panel discussion about the issue last week.
“I think it’s a conversation that still needs to happen and there’s no project still, so now is when that discussion needs to happen to figure out what makes the most sense,” said Adam Agalloco, the city’s Energy Manager at the forum, held at Jefferson University.
Agalloco said his agency is looking to the public to help find the right LED for the city. He said city officials will take into consideration AMA’s guidelines that recommend minimizing and controlling blue lighting to reduce glare and encourages the use of 3000K or lower lighting temperatures for outdoor installations.
“The AMA is a serious organization, so we need to look at that,” Agalloco said.
The city’s choice could have serious implication for its avian residents and passers-through. Intense beams of lights coming from buildings or roads also pose a high threat for tens of millions of birds that migrate through Philadelphia every year, said Keith Russell, program manager for urban conservation for Audubon PA.
“If you have migrating birds that are going over a city at night, and most birds migrate at night, all the ambient light can be disorienting to them,” Russell said at the forum. “They need darkness to use the cues they’re using to find their way — they use the stars, they use the setting position of the sun, and they detect the earth magnetic field — and lights can interfere with their ability to do all of these things.”
Although all bright lights can be harmful, the effect of LED can be greater because of their potential for greater brightness than conventional lamps, Russell said. One benefit of the LED makeover, however, is the amount of control a user can have over the light source.
As opposed to a standard street lamp, LEDs can be programmed, so intensity dims at certain points in the day. Timers or sensors can be used to shut down the lights when they’re not needed. And the beams can be directed to better reach their targets.
“Audubon is already in conversation with the energy department here in Philadelphia, so they’re aware of these issues,” Russell said. “As we go forward and replace our street lighting with LEDs, I hope these precautions are put in place.”
Richard Montañez, the Street’s Department Deputy Commissioner, said in an interview that the city is already experimenting with dimming some of its LED lights in the middle of the night to reduce light pollution. The lights would be fully restored at 5 in the morning, he said.
According to the city’s Office of Sustainability energy master plan, lighting the streets currently ranks as the city’s top electricity suck. The LED remake is, accordingly, the city’s number one strategy for increasing energy efficiency. The plan will cost tens of millions of dollars and take years to accomplish but could reduce the city’s carbon emissions by 13.7 thousand metric tons.
The process began in 2015, but today, only 3,708 out of the city’s 105,000 street lights are LEDs. Of the city’s 18,000 alley lights, 2,903 have made the switch. A spokesperson for the city said that the process is still in its early phases and it is too soon to know when the full rollout will be done.
Although most of Philadelphia’s LEDs streetlights are 4000K — Montañez said that was AMA’s recommendation when they were installed — the Street Department is trying out lower color temperatures such as 3500K.
“I don’t want to say that the city will be a 4000K city forever because, as you know, technology changes and I need to make sure the city stays up with it — but as of today, we’re a 4000K city until we can find something that works with not only the AMA but also the public safety aspect.”
The Streets deputy commissioner said 4000K LEDs does not make the streets safer per se, but it allows them to recognize faces and colors when using surveillance cameras. With a conventional 2700K high-pressure sodium light or a 3000K LED light they can’t tell the color of the shirt of a suspect in a video, whereas, with a 4000K they can, he explained.
When the Delaware Valley Regional Planning Commission started a project to install 26,000 LED street lights in 35 municipalities in Bucks, Montgomery, Chester and Delaware counties, Liz Compitello, DVRPC’s senior research analyst in charge of the project looked closely at the possible human impacts of LEDs.
Compitello said although the science says that blue light exposure during the night can impact sleep pattern and LED tend to have more blue light content than other conventional lighting sources, there’s very little research on the specific impacts of blue light coming from LED streetlights. The AMA report, she said, is based on extended exposure to high-intensity LEDs, but people are not supposed to be exposed to streetlights during long periods of time. Compitello added that LEDs streetlights can reach their target more effectively because you can control the direction and intensity of the light they emit, and therefore reduce light pollution and that although they do have a higher percentage of blue light per lumen, they need fewer lumens than conventional lighting to generate high-quality light.
“Color temperature is not always the most accurate measurement of blue light content within the light — there’s lots of other factors that go in there,” Compitello said. “So it could potentially be a 4000K lamp that has similar blue qualities than a 3000K. 3000 and 4000 is really a measure of your perception of the warmth of light not exactly how much blue light is coming out of that source.”
The DVRPC project installed 3000 and 4000K in different municipalities, depending on their decisions. Some prefer the 4000K because they looked brighter, Compitello said.
“If you’re driving around, a 4000K light is going to look more like daylight, and it’s going to be easier to see the things in front of you potentially than a 3000K,” Compitello said. “So some municipalities that were more concerned about roadway safety and pedestrian safety may have been leaning more towards 4000 over 3000 because of the quality of light it generates.”
Neither Philadelphia’s Street Department nor the DVRPC have received a lot of complaints from residents exposed to 4000K lights. And if they do, they install house side shields or change the lighting optics. On the other hand, the Street Department said many civic and community groups have requested brighter lighting.
“Unfortunately this is kind still new, and nobody knows — we keep trying to figure out which way to go,” said Streets deputy commissioner Montañez. “We’re not there to light up somebody's house; we’re there to have a city at night, especially in Center City, where people can walk and want to be in it.”
Jeffrey Kahn, a senior lighting designer at Beam, has worked on many streetscapes using LED lights and is currently working with Tacony CDC. He said complaints of residents are minimal.
“LED technology had a pretty bad name in the early days as being glary and blue,” Kahn said. “Ten years ago I would not have been suggesting LED streetlights, and now I wouldn't suggest anything but an LED streetlight because there are many more options now where the luminaire does not have that ghostlike cast and is often indistinguishable traditional light sources.”