the highway lamps

What too much artificial light steals from our night skies

The light on your porch or the streetlights in your neighborhood probably don’t come to mind when you think about pollution. But as artificial light has increased over the years, its far-reaching implications have grown more apparent. Across the globe, amateur and professional astronomers alike are illuminating those consequences, and some communities are taking action.

Since widespread use of lightbulbs ramped up over a century ago, we’ve no longer been exclusively governed by our planet’s built-in bedtime — a natural cue for our own circadian rhythms that also influences how plants and animals go about their lives.

“Essentially, we’ve upended that in the last 100 years by the rapid and ever-increasing growth of artificial light at night,” said Ruskin Hartley, executive director of the International Dark-Sky Association (IDA).

Light pollution has been on the rise for decades. In North America alone, light emissions rose by around 6 percent annually from 1947 to 2000, according to research published in 2003.

Animation by Megan McGrew/PBS NewsHour

Observable light emissions increased globally by at least 49 percent from 1992 to 2017, a study from the University of Exeter this year found. It also emphasized that, due to measuring limitations, the actual increase is likely much higher — as much as 270 to 400 percent depending on region.

Light becomes pollution when it’s not serving a useful purpose, according to Hartley, and that can waste energy, racking up a hefty price tag and contributing to our carbon footprint.

Light pollution can take a few different forms, as defined by the IDA. “Clutter” is an often-disorienting combination of multiple, excessively bright light sources, like Times Square or Las Vegas. ”Glare” is when super-bright street or headlights hurt your eyes or make you squint in discomfort. ”Light trespass” is when light shines where it’s not supposed to, like a streetlight streaming into a bedroom window.

If you’ve ever had to buy blackout curtains to help you sleep better, you already know that excess lighting can have negative effects on living things. People who are exposed to a lot of artificial light when it’s dark outside may be more prone to insomnia. And artificial light can throw off plants and animals in myriad ways, from disorienting birds and making it more likely they will fatally collide with buildings, to helping drive a massive insect population decline worldwide.

In Pittsburgh, the city council recently approved a Dark Sky Ordinance after years of local advocacy that will pave the way for less wasteful, more eco-friendly light fixtures for streetlights, parks, playgrounds and buildings located on city property.

Astronomer Diane Turnshek, who’s based at Carnegie Mellon University in Pittsburgh, said it will be the first city to follow the IDA’s newest guidelines, but it’s not the first to address light pollution on the local level. Flagstaff, Arizona, was the first city to receive official “International Dark Sky Place” designation in 2001, but it enacted the first-ever outdoor lighting ordinance back in 1958, according to the IDA.

When Pittsburgh begins to replace its lights early next year, it will swap in new LED light fixtures that emit a softer, warmer light compared to harsher LED lights that are more commonly in use today. The swap will involve around 40,000 existing lights that currently use either traditional LEDs or older high-pressure sodium bulbs, and the city also plans to add several thousand new street lights in order to improve light equity — the balanced distribution of artificial light — across the city.

View of the Pittsburgh skyline at night, from Mount Washington, Pittsburgh, Pennsylvania

View of the Pittsburgh skyline at night. Photo by Getty Images

Whether the effort successfully curbs light pollution in the city remains to be seen, but the shift to new lighting is expected to have significant energy and long-term cost savings for Pittsburgh.

Grant Ervin, chief resilience officer for the city, noted that many people in urban environments can’t see the stars where they live.

“The ability to see the night sky is a pretty magical thing,” Ervin said. “And hopefully we’re opening up that opportunity for Pittsburghers to enjoy that benefit.”

Artificial light has changed a lot over the decades

Nowadays, the most efficient light bulbs on the market are broad-spectrum LEDs. They excel in long-term cost and energy benefits — and require significantly less maintenance compared to other bulbs — but they also pose a few problems. For one, the fact that they’re broad spectrum makes it much harder for amateurs and astronomers based in more urban locations like Pittsburgh to observe the night sky.

In the past, Turnshek said, common outdoor light sources like high-pressure sodium bulbs released a warmer, amber light that encompassed a comparatively smaller section of the visible light spectrum. Astronomers could use a filter to block that light out from their telescopes in order to see the sky properly.

“The [visible] spectrum goes from long wavelengths — which are your reds — to short wavelengths, which are your blues,” said Stephen Quick, a professor at the Carnegie Mellon University School of Architecture. Both he and Turnshek helped draft Pittsburgh’s Dark Sky Ordinance, and led local efforts to raise awareness about light pollution.

“You can’t [filter out] a full-spectrum light because if you start to filter out all the colors, you have no light,” Quick explained.

LEDs also emit a higher amount of light on the shorter, bluer side of the visible spectrum, not unlike the kind we get from our phones and laptops. That’s why they tend to look more cool and harsh to our eyes compared to other types of light. But newer bulbs can feature a coating that filters out some light from that side of the spectrum, allowing warmer, redder light to shine through that’s more comparable to old-school bulbs.

And yet, the only way to curb light pollution, advocates say, is to avoid lighting up places that don’t need to be illuminated, and being more intentional about how much and what type of light is used in ones that do.


Earth at night, showing the lights of the Americas. Photo courtesy NASA’s Earth Observatory

Some critics may raise safety concerns in response to the idea of reducing nighttime lighting. But advocates argue that excessive lighting offers the feeling of safety more than actual protection, and that quantity doesn’t necessarily equal quality. The glare caused by excess light, for example, can both irritate your eyes and impede your ability to see clearly while driving, potentially compromising your own safety and that of others.

“There’s the perception that light makes us safer and, because some light makes us safer, therefore more light must make us more safe,” Hartley said. “And the reality is, as you start to look at it, actually quality light can enhance safety at night, and that’s really about using it in the right way.”

The consequences of light pollution and how smarter lighting can help

Much more research is needed to investigate the health implications of light pollution, and to determine just how much light exposure is potentially harmful. But we know that a slew of medical issues can stem from a disrupted circadian rhythm, our inner biological clock, which is regulated in large part by light. A 2017 Harvard study found a correlation between breast cancer rates and higher exposure to light at night that was particularly strong among women who worked night shifts.

There’s also evidence that the burden of exposure to light pollution falls disproportionately on communities of color. A 2020 study from the University of Utah found that, when adjusted for population differences, Asian, Hispanic and Black people in the United States were on average exposed to twice as much light in their neighborhoods than white people.

“It’s the same story playing out again and again in terms of the relationship with these disadvantaged, marginalized communities and a whole suite of pollutants,” Hartley said.

The light fixture that’s most friendly to the environment, Hartley said, is the one that’s never turned on. When it comes to designing lighting, he advocates for starting “with natural darkness and [adding] light where you need it.”

Advocates emphasize that, compared to many other types of pollution plaguing our planet, addressing excessive lighting is relatively straightforward.

“It’s not like soil pollution or water pollution or plastic in the ocean. It’s an easy one to fix,” Turnshek said. She said that part of understanding the negative effects of light pollution requires reevaluating our own cultural association with light as inherently safe and positive, and dark as something that is dangerous and frightening.

Her own love for the night sky — along with teaching a steady stream of astronomy students who’d never personally seen the Milky Way — encouraged her to start spreading the word about light pollution in the city years ago. She argues that there’s a lot at stake when it comes to slowly losing sight of the cosmos.

“I think we lose the fact that we’re all connected. We’re all under one sky,” Turnshek said. “This planet is planet A, there’s no planet B. We have to take care of it.”

And according to Ervin, the new ordinance is one step toward “reclaiming” the sky for Pittsburghers.