The International Dark-Sky Association has summarized more than 300 peer-reviewed studies on the effects of artificial light at night in an effort to help dark-sky advocates.

Milky Way soars above horizon of Top of the Pines
Most people don't have easy access to a view like this one. The International Dark-Sky Association declared Michigan's Top of the Pines an International Dark-Sky Park last year. Dark-sky places have policies to preserve dark skies, a vanishing natural resource.
Val Szwarc

Those aged 30 and younger may never have experienced a truly dark night sky. And if no action is taken, they never will.

Every year, the remaining dark patches on this planet shrink as both the amount of artificial light used and the area it covers grow by about 2% per year. And satellite “megaconstellations” add to terrestrial light pollution in even the darkest skies.

The changes go largely unnoticed because it’s difficult to perceive what we’re losing so gradually yet persistently. What’s more, humans tend to like artificial light: Light is good, so more light is better, isn’t it?

But thanks to an increasing scientific interest in the topic, we now know that artificial light at night (ALAN) has detrimental effects that range far beyond astronomy: on human health, wildlife reproduction and ecology, public safety, and energy consumption.

The average number of studies on light pollution and its detrimental effects has increased by more than 1,000% since the year 2000, and dark-sky advocates struggle to keep up. So the International Dark-Sky Association (IDA) has published a comprehensive report summarizing what we know, called “Artificial Light at Night: State of the Science 2022.”

“Our goal was to provide dark-sky advocates with a reliable summary of science results in accessible language that will help them explain the issues to others,” explains coauthor John Barentine (Dark Sky Consulting). The 18-page report is an outgrowth of IDA’s “Artificial Light at Night Research Literature Database,” which lists over 3,500 scientific papers; the report referenced 321 of these.

LED Lights

Artificial light at night on world map
A composite image shows artificial light on Earth at night. The amount of light pollution has only increased since the introduction of power-saving LEDs due to misuse.

Those new to the dark-sky activism will encounter some unsettling insights, including the misuse of LEDs. Advertised as “eco-friendly” because of their lower energy consumption compared to other light sources, LEDs are replacing older technologies world wide — and they are one of the key culprits for recent increases in global light pollution. As light becomes cheaper, people use it more lavishly, a well-known rebound effect. In addition, LEDs typically emit lots of bluer light, which, as many of the cited papers attest, is especially harmful to wildlife, human health, and astronomy.

“Blue is the wavelength which most strongly interacts with the circadian rhythm in humans and many other species,” says Etta Dannemann, author of Light Pollution – A Global Discussion. “As energy efficient as LEDs might be – this is the reason why they are more disruptive to nature. It’s a problem that many who plan and install lighting are unaware of.”

Safety vs. Health

Lights are widely employed to prevent crime and improve road safety — even though studies have shown mixed results as to whether they actually do so. The report concludes that decision makers often substitute their intuition in cases where scientific guidance is lacking.

The effects of the resulting overuse of lighting are clear: Mounting evidence shows that light pollution contributes to the mass extinction of pollinators and other nocturnal insects. Besides ecological effects and cost increases, the resulting over-lighting can itself create a safety hazard, such as when it is poorly designed or causes glare.

Artificial light at night can also wreak havoc on human hormonal systems, playing a role in certain cancers and cardiovascular diseases. By changing the behavior of nocturnal animals, such as bats, light pollution might even contribute to the emergence of new diseases like COVID-19. However, scientists still debate the influence of outdoor vs. indoor light at night on humans, and other stressors and pollutants also contribute to negative health outcomes.   

Good Lighting Guidelines
Sometimes light at night is necessary. Following these guidelines, light can be provided when and where it is needed.
International Dark-Sky Association

Satellites at Night

In addition to summarizing studies to date, the report also lists knowledge gaps and open questions. For example, what will happen as humans continue to launch increasing numbers of satellites? Thousands of satellites in low-Earth orbit will not only streak through twilight skies, but their cumulative effect will also brighten the night sky itself.

Researchers, among them Barentine, calculate that satellites and debris have already increased sky glow by about 10%. “That’s less than the typical airglow intensity, and measurable only above the airglow layer,” he says. But if companies build-out all the currently planned satellite constellations and generate the expected space debris, then by 2030 space-generated light pollution may begin to compete with terrestrial light pollution. This is particularly bad news for rural areas that are otherwise still dark.

“I personally don't expect that to happen, but it's possible,” Barentine says. “The most important aspect is limiting the amount of debris in order to prevent that outcome.”

For anything to change, we first need to know about it. As such, the IDA plans to maintain the report as a “living document,” with updates to account for future developments. Anyone can freely use the text as talking points in letters and presentations or use it as a “leave behind” item when speaking with decision-makers. While science provides data, it’s up to activists to use them and save us from a night too bright for stars.


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June 22, 2022 at 7:31 pm

Thank you so much for this timely article.

I have lived west of the Kansas City metro for the past 21 years. When we moved to this largely wooded neighborhood surrounded by farmland, we did so because there were NO street lights!! Today, we STILL have no street-lighting!! However, in the last 5 to10 years, our night sky has dramatically brightened. Many new housing developments, schools, and even a hospital now occupy what was once prairie or cultivated land. This growth, and the advent of the LED security and street lighting, have been the culprits. I would point out that even when lights are shielded - all the LED street lights in our area cannot be seen until you are almost under them - and directed downward, they are so insanely bright, that a significant percentage of this light reflects up into the sky!!

Once upon a time, I had no trouble observing M 31, the Andromeda Galaxy, with the naked eye from our driveway. Today, I'm doing well if I can just barely catch fleeting glimpses of it using averted vision! The summer Milky Way was an obvious presence on moonless nights, but these days it is difficult to see the Cygnus and Scutum star clouds even when they straddle the meridian! However, I continue to observe what I can from where I am with the instrumentation I have. I got started in astronomy in 1968 living in Woodland Hills, a suburb of Los Angeles, CA, and just about ANY sky I see is better than that!! Somehow, though, I thrived there! That hideous light pollution was no match for Comet Bennett in April of 1970, or the total lunar eclipse following the February 9, 1971, Sylmar Earthquake.

The satellite issue was pointed out in the writing of Leslie C. Peltier from his moving autobiography, "Starlight Nights," when he prophetically wrote in 1962 or 63: "In these strange lights that cross the sky my two scopes see a gloomy portent, a distant early warning of the nights to come. Forty years ago, on the top of Mount Wilson, the world's largest telescope could look down and see the gathering lights below. Today the approach is from above as well." The skies of the early 1960's were a dream compared to the nightmare blitzkrieg of low-Earth orbit currently underway. I feel sorry for those professional and amateur astronomers whose primary astronomical pursuits require photography.

Future observers may look back on these present times as the halcyon days. Does the planet Coruscant ring any bells?

Doug Z

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Alain Maury

June 23, 2022 at 7:13 pm

Am I the only one not being able to reach the link "Artificial Light at Night Research Literature Database" ?

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Jan Hattenbach

June 24, 2022 at 8:20 am

Hi Alain, the link worked when I checked it, but you are right, it's not working now. Try instead!

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June 25, 2022 at 12:58 pm

Hi Jan Hattenbach, A great summary article/post on IDA's recent publication on State of Science concerning light pollution. And I am flattered that you have used my astrophoto of the Milky Way as seen from Top of the Pines (TOP), an IDA Dark Sky designated Park in Ouray County, Colorado - in Southwest Colorado at an elevation of 8600ft - just for the record. More info on TOP and it's Dark Skies can be found at

Val Szwarc - IDA Advocate and TOP member of the Board

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June 28, 2022 at 4:21 pm

I live just ~25 miles up the road from you, in Montrose. I moved over here more than a decade ago (from the Front Range) for the dark(er) skies, but I've watched them deteriorate.

With a night sky meter I can monitor everyone turning off their porch lights during the evening, and I get a blip of increased darkness when they turn off the lights at the event center parking lot, or at the high school stadium.

Even at its best, light pollution is ~150% of the natural background, meaning about a magnitude brighter.

Even though nearby Black Canyon of the Gunnison Nat'l Park is a designated site you'd never know it from the outdoor lighting in the housing developments going up here. Public awareness is virtually nil: we have no local TV stations, the radio stations just play music and national news, and the newspaper (and other local publications) get too much advertising revenue from the real estate industry to ever run anything critical of them. I'm not sure how anyone except a few will ever recognize dark skies as a valuable resource.

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October 25, 2022 at 1:08 pm

All the bortle 1's are west of a N/S line at big bend national park.

I've seen some stuff on light pollution and planets I believe is incorrect. Detail on some of the planets like Uranus and it's moons seems to be affected tremendously by light pollution.

With comet coma/ tails etc light pollution tremendously affects observations.

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