Planet EarthPlanet Earth

    Why light pollution is a solvable environmental crisis

    Excessive outdoor lighting is deadly to animals and takes a toll on human health and wellbeing, too. But when it comes to large-scale environmental problems, this one may be a relatively easy fix.

    ByAlissa GreenbergNOVA NextNOVA Next

    A long exposure shows insects drawn to a halogen street light in the city of Mazatlán, Mexico. Image Credit: Matt Mawson, Getty Images

    It’s not easy to make street lights exciting, but Kelly Beatty is trying. Holding court over Zoom on a spring evening in 2021, he warns citizens of Nantucket island in Massachusetts that the decisions they’ll soon make about their lights are choices they’re “going to have to live with for a long time.” 

    Beatty often helps advise communities like Nantucket as they transition their streetlights from traditional bulbs to more energy-efficient LEDs, or light-emitting diodes. As communications officer of the Massachusetts chapter of the International Dark-Sky Association (IDA), he’s well aware of the stakes. As this process has been repeated in towns across the world, it has led to a new and preventable environmental problem. LED lights can last 20 years or more, he reminds the group. “It’s important to get it right when you have a chance.”

    The IDA defines light pollution as the inappropriate or excessive use of artificial light, with variations including glare (excessive brightness that causes visual discomfort), skyglow (brightening of sky over inhabited areas) and light trespass (light that falls where it isn’t intended or needed). Already a growing problem, light pollution has intensified with the rise of LEDs, which produce blue-intense light in shorter wavelengths that are more susceptible to scatter and thus travel farther. An estimated 99% of U.S. and European populations now live under light-polluted skies, and one third of humanity is unable to see the Milky Way at night. From marine life and plants to birds and insects, the loss of darkness has left deep scars in our ecosystems.

    Twenty-five miles off the coast of Massachusetts, Nantucket is one of the darkest places left on the Eastern Seaboard—but even its skies are lightening. As they fight for their darkness, many Nantucketers taking up the cause see light pollution as the rare environmental threat where individual people can make a real difference. “It’s easier to solve than many of the other serious problems we have on Nantucket,” like erosion or affordable housing, says Gail Walker, founder of the local activist organization Nantucket Lights. “If we can educate people and help them understand the problems, most people are going to get on board.”

    The night sky as seen from the Middle Moors on Nantucket. Image Credit: Bill Hoenk Photography

    The problem of light pollution started in earnest with the widespread installation of streetlights, which coincided with the rise of highways in the 1950s and 60s. “Think about society then: Everything closed at 8 or 9, and they rolled up the sidewalks,” Beatty says. “We did not have a 24/7 society like we have now.” With highways came all-night gas stations, drug stores, and grocery stores. And, above all, streetlights by the tens of millions. 

    Then, in recent decades, lightbulbs made with LEDs arrived, a revolution in energy efficiency with seemingly little downside. After all, an LED bulb converts some 90% of the electricity it uses into light, whereas a conventional incandescent bulb only converts about 10%. And LED bulbs are touted as lasting up to 25 times longer.

    But the physics of LEDs make them fundamentally different from incandescents. While those traditional bulbs put out warm white light made of all colors mixed together, LEDs filter blue-rich light through a specialized phosphor material, producing light that appears white to the human eye but is still more blue-intense than incandescents’ light.

    But blue light is also the most disruptive to our nighttime environment because it mimics daylight, disrupting the hormone production and sleep cycles of both animals and humans. Melatonin, one of those hormones, helps the immune system destroy renegade cells dividing out of control. That can lead to other health issues, including heightened rates of cancer. And, “we’re not the only ones who produce melatonin,” says Mario Motta, a cardiologist and trustee of the American Medical Association. “Even amoebae produce melatonin”—meaning even amoebae might be vulnerable to light at night. 

    Two geckos in an outdoor lamp in Córdoba, Spain. Studies indicate that insect predators like bats, lizards, and toads will station themselves near artificial lights, where they can easily pick off prey. Image Credit: Clemente Crisci / EyeEm, Getty Images

    The impacts of light pollution are evident everywhere from human health to astronomy research, but they come into particular focus in the recent phenomenon of global species die-offs. Between 100 million and a billion birds die every year due to light pollution, according to Massachusetts IDA chapter president James Lowenthal. New York City recently dealt with a huge die-off, “with flocks of migratory birds slamming into buildings,” says Sarah Bois, an ecologist at the island’s Linda Loring Nature Foundation and a member of Nantucket Lights. “They’re attracted to light.” A 2015 study at New York’s 9/11 “Tribute in Light'' installation showed an increase from 500 birds within half a kilometer of the light beams before they were turned on to 15,700 just minutes after.

    The issue is a double whammy for birds because they rely on insects for food—and those populations are plummeting, with light pollution contributing significantly to the so-called “insect apocalypse.” By some estimates, one third of insects attracted to light sources at night die before morning, either due to exhaustion or because they get eaten. And according to a study in Germany, the number of insects in that country alone that die after being attracted to lights can number 100 billion or more in a single summer. 

    Some starve to death searching for food that should appear bluer at twilight but is lit up amber under streetlights, says insect conservationist Avalon Owens, a doctoral candidate at Tufts University. Some are thrown off by light just the way we are, because of their circadian rhythms. Pollinators whose schedules are altered by artificial light miss the flowers they’re evolutionarily paired with, if the flowers naturally close and open with the warmth of the sun. And insects that rely on circadian rhythms for their yearly development don’t hibernate in time for winter and freeze to death.

    On Nantucket, these phenomena are of particular concern because the island is home to a remarkably healthy population of northern long-eared bats, which are endangered. Like many birds, the bats rely on insects for food and are easily dazzled by light, putting them in increasing jeopardy. Jack Dubinsky, director of the Maria Mitchell Aquarium on Nantucket, says he’s concerned that adding increasingly lit-up nights to the challenges of climate change, water quality, and ecosystem collapse could put huge pressure on some already struggling species. “The more curveballs we throw, the less likely they’ll be able to find their way,” he says.

    A composite of nighttime images taken by the Suomi National Polar-orbiting Partnership satellite in 2012 shows light pollution in the contiguous United States. Image Credit: NASA Earth Observatory

    For Beatty, the first step in addressing the issues wrought by light pollution—and LEDs in particular—is to look at color temperature, which is measured in kelvins. Lower temperatures like 2,000 K correspond to warm reddish or yellowish light (think candlelight) while higher color temperatures like 4,500 K and up correspond to harsher, bluer light (think blue sky). “When LEDs started getting rolled out for streetlights, the most common ones were very close to this native, blue-rich light,” since they were also the most energy efficient, Beatty says.

    But because the white light of most LED bulbs is produced by coating a blue-intense LED in phosphor material, it’s possible to switch out that phosphor for one that absorbs and re-radiates the light to be less blue and look warmer, using the same technology already common in fluorescent bulbs. A new wave of LEDs, known as PC Amber, have color temperatures as low as 2,200 K and are gaining popularity.

    Beatty also points to another solution built into LED technology. Beyond being highly efficient, LED bulbs “can be controlled in amazing ways, programmed with central computers,” he says. Cities like Cambridge, Massachusetts, have programmed their LED streetlights to reduce to 50% power at various points during the night, depending on the street. A few towns in Europe have opted for motion-sensing lights that turn on and off as needed. Older-style lighting worked best if left on continuously through the night, Beatty says. But “LEDs don’t mind being turned on and off or dimmed up, down sideways, multiple times per second,” he says. “You can do anything you want to them.”

    In 2012, the American Medical Association declared light at night carcinogenic, which has helped drive policy change in cities across the country. New York City drew criticism from the IDA when it began replacing its streetlights with LED bulbs, some at color temperatures as high as 4,000 K, but changed tack when residents complained, citing the AMA guidance. (It helps that high-color-temperature lights are “universally hated,” Beatty says.) Since then, initiatives like Audubon’s Lights Out New York have also convinced managers of major structures like the Chrysler Building to go dark from midnight to dawn during the fall bird migration season. And the city has reached an agreement to turn off for short periods the 9/11 memorial lights that were leading to so many avian deaths, allowing the trapped birds to continue their journey.

    In Chicago, which was famous in light pollution circles as the most over-lit city in the country, the city has been gradually replacing its streetlights with 3,000 K LEDs, which it  touted as saving the same energy as taking 2,400 cars off the road. Tucson, Arizona, reduced its lighting emissions by 60%, in part by switching to 3,000 K LEDs and programming them to dim late at night. And in fall 2021, Pittsburgh passed the nation’s first dark sky ordinance that will involve replacing both its older-model conventional streetlights and more recently installed high-color-temperature LEDs with warmer, fully shielded lights equipped with motion sensors.

    Phoenix, Arizona, illuminated at night. In 1988, two astronomers noticed the brightening glow of nearby Tucson, Arizona, was threatening the dark skies at Kitt Peak National Observatory. They were "the first ones to raise the alarm about light pollution,” Kelly Beatty says. Image Credit: Andy Ryan, Getty Images

    Beatty encourages concerned citizens to get involved with local conversations about light at night—both about streetlights and policies around new construction. “The time to be proactive is when developments are being proposed,” he says, since it’s much easier to convince developers to make changes to their lighting plans when the buildings aren’t already set in literal stone. “Most times people install bad lighting because they don’t know any better,” he says. “It just takes one person to say ‘Hey, there’s another way to do this.’” That’s one reason he came to Nantucket’s meeting about streetlights.

    “We find the people most concerned about light pollution are not big cities but in rural areas,” he adds. And in that observation he sees a powerful advantage in the fight for dark skies. Since the causes of light pollution are hyperlocal, changes made by individuals and small groups can make a quick and observable difference, which empowers them to continue that work. “Every place where we can energize and educate local citizens is a victory, however small,” he says. “There are hundreds of people like me across the U.S. who are advocates for this, who insert themselves into local situations where education is desperately needed.”

    Gail Walker had already been watching Nantucket’s brightening skies when she learned about the IDA and its mission. The vivid stars over empty, windswept beaches had always been one of her favorite things about the island, and she wanted to preserve that experience for her grandchildren. Walker has earned a reputation locally as a go-getter, a retired attorney with a knack for bringing people around to her point of view. After coordinating the March 2021 forum on light pollution with Beatty, she began work in earnest with Nantucket Lights, bringing together concerned citizens to raise awareness and shape the community’s response.

    From there, conversations on the island evolved quickly. Walker began advising homeowners associations about their lighting policies, connecting local groups with lighting experts, and helping assess citizen complaints about lighting issues. She is also shepherding the community’s planned application to become an official International Dark-Sky Community.

    To be fair, Nantucket has a few key factors that give it an advantage in these efforts: a law governing outdoor lighting already on the books, an affluent community with an interest in maintaining a certain ambience on the island, and officials who see the benefit of that ambience for tourism. But to Walker, a significant part of her success so far is that light pollution “is a solvable problem.” Unlike other issues, which might seem too big, complex or intractable, she says, “there’s kind of an easy fix.”  

    Motta and Beatty suggest starting with the five principles the IDA has established toward what Motta calls “sane outdoor lighting,” guidelines that individuals can follow to make better lighting choices in their own homes. Those guidelines include an emphasis on light that is useful, or toward a purpose; and targeted, or directed only where it's needed and otherwise properly shielded. Lights should also be no brighter than necessary. And it’s best to avoid high-color temperature, bluer light as much as possible. “That’s it,” Motta says. “Follow those simple rules, and we’ll have a much better world.”

    Owens, the entomologist, agrees. When it comes to adjusting our night light to help insects, “The most important thing is to ask, ‘Are you using the light?’” she says. “ If not, don’t have it.” She’s a proponent of flashlights, motion detectors, and timers, all the gadgets that might help keep light inside a building. “Automated curtain technology is the next big thing,” she jokes. “Who’s against closing your curtains? Nobody, but it’s hard to remember.”

    The Milky Way stretches above the Maria Mitchell Association's Loines Observatory in Nantucket, Massachusetts. Image Credit: Charity Grace Mofsen

    On a breezy fall evening with a nip in the air, Nantucket’s Maria Mitchell Association is hosting about 50 visitors on the small platform between the domes of its observatory’s two telescopes—both currently trained on Jupiter to allow observers to admire its stripes. Overhead, clouds glide by soundlessly, reflecting a glow from the north that marks a grocery store and cluster of brightly lit schools. “You can see how they’re reflected up above, leaking up into the sky,” association Director of Astronomy Regina Jorgenson says, pointing. The distant light from Cape Cod is even visible occasionally, she says, on humid nights when moisture in the atmosphere scatters light farther.

    Still, in breaks in the mist, she’s able to point out the sugary trail of the Milky Way. The upturned faces of tonight’s crowd reflect awe at the sight. Many island visitors have never seen the Milky Way before. “The first time they see it, it’s a transformative experience for them,” she says.

    Jorgenson has been involved with the observatory since her internship here in 1997 and, along with her astronomy research, is dedicated to preserving the legacy of Maria Mitchell. Mitchell, America’s first professional woman astronomer, was born on the island in 1818. She gained fame for discovering a comet and became the first woman to be inducted into the American Academy of Arts and Sciences. Almost a century later, an NSF-funded internship at the observatory has become a key source of support for female astronomers in the U.S. Jorgenson is determined to protect that resource—and the dark sky that makes it possible. 

    Watching the night grow inexorably brighter over the decades from her observatory perch outside town has been “scary” she says, but she remains hopeful. Nantucket’s geography, history, and culture makes so many things possible, she says. 

    “We’re a small enough community that we have power to make a quick and effective change.” 

    Correction: Nantucket is roughly 25 miles off the coast of Cape Cod, not 12 miles as previously stated.

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