Light Pollution: Everything You Need to Know

Quick Facts

• There are four main types of light pollution: skyglow, glare, light trespass and clutter.
• Human development, thoughtless behaviors, and poor light fixture design contribute to light pollution.
• The vast majority of the populated planet cannot see the natural night sky because of light pollution; fewer still are the number of Americans or Europeans who can.
• Human health impacts have been tied to light pollution exposure.
• As many wild creatures rely on natural sunlight and moonlight conditions to complete critical life functions, like reproducing or migrating, light pollution weighs heavily on their ability to do so.
• Experts say light pollution is a sign of energy inefficiency.

What is Light Pollution?

Whether you’re walking along a cul-de-sac sidewalk or headed to a neighborhood restaurant for dinner, you’ll be hard-pressed to find a residential or commercial neighborhood that doesn’t have an abundance of lights to guide the way. And unless you’ve ever lived in a truly rural area, chances are that you’ve always lived with more lights around you than visible stars in the sky above.

But that abundance isn’t simply a harmless excess. A form of environmental harm that many of us in more densely populated areas have become acclimated to, light pollution is associated with a range of issues, including wildlife conservation and climate change, according to several experts.

While other forms of pollution are widely accepted as environmentally negative, “we haven’t had that discussion with artificial light,” says Ashley Wilson, director of conservation with the International Dark-Sky Association.

“Even the regulatory bodies, like the Illuminating Engineering Society, provide their recommendations, but the recommendations include minimum values and not maximum values,” she explains. “Communities will often opt to have lights brighter than these minimum values because they feel like it would make them more safe [but] it’s not really based on any research. or are testing.”

What are the Different Types of Light Pollution?

There are four main types of light pollution, according to the International Dark-Sky Association, the main organization focused on light pollution and its repercussions. 

Skyglow is the combined illumination of all the light sources that creates an artificially bright arch in an urban area at night.

Glare is gratuitous, bright light causing discomfort or pain — like when you’re driving at night and another driver has left their high beams on.

Light trespass is when a light beams where it shouldn’t, unintentionally “trespassing.” That can look like a street light beaming straight into your bedroom at night.

Clutter is when too many sources of light are bunched together and cause confusion. A row of street lights without shields to direct the light downward can be a source of light clutter. 

What Causes Light Pollution?

Light pollution comes from artificial sources of light, of course. However, the concept of light itself doesn’t necessarily equal pollution in any and all forms. A source of light becomes a source of light pollution typically because of the density, design or improper use of the fixture.

Increased development means more high-rise condominium buildings and skyscrapers to sprawling suburbs and downtown streets — and more people installing and turning on outdoor lights throughout the night, even if the benefits of doing so aren’t always clear or identifiable.

“The mindset has always been that ‘dark is bad and light is good,’ so more light is better and we also have thoughts that if you light up a place, crime goes away,” says Paul Bogard, an associated professor of English and environmental studies at Hamline University in Minnesota who wrote The End of Night: Searching for Natural Darkness in an Age of Artificial Light. “There’s not a lot of evidence for that, but we still have that mindset.”

The light design is another problem, as fixtures are often inefficient and indiscriminate as to where their beams of light hit. Wilson noted that since brighter, whiter lights are popular, “manufacturers are happy to make products that people are ordering.”

“We just have this [LED] technology that allows us to pump out more lights … more efficiently from a cost standpoint, but we haven’t changed our thinking about light,” says Bogard. “One example is that a lot of the light fixtures that you see, the designs of those fixtures were created for gas lamps.” Those lamps, Bogard explains, were dimmer and less efficient than the bulbs we use today, so casting a wider illuminance made sense at the time, but that’s no longer the case.

What Places Have the Most Light Pollution?

Light pollution is a problem almost all humans encounter on a daily basis. According to a 2016 study published in Science Advances, over 80% of the planet lives under light-polluted skies. That number shoots up to over 99% when looking at only Americans and Europeans. 

Maps that accompany that study show the ratio of artificial light to natural light across the planet. The most light-polluted hot spots appear concentrated around the planet’s largest cities, with significant streaks throughout even many areas where the population isn’t dense. No countries seemed to be without at least some amount of light pollution

How Are Humans Impacted by Light Pollution?

Artificial light messes with our circadian rhythm, the instinctual beat humans follow to know when to wake up, go to sleep and carry out other natural processes. 

Wilson notes that “many studies have proven that exposure to artificial light leads to increased rates of cancer — like breast cancer and prostate cancer — as well as increased rates of diabetes.” Her organization, the International Dark-Sky Association, also says that exposure to artificial light at night can increase “risks for obesity, depression [and] sleep disorders.”

What Animals Are Impacted By Light Pollution?

Given that humans are impacted by light pollution, it makes sense that the rest of the animal kingdom is, too. The life cycles of many creatures — from foraging to migration and more — are dictated by the amount of moonlight there is during the lunar phase, according to Wilson.

Here are some of the many wild species that are affected by artificial light pollution.

Birds

Migratory birds face dire threats from light pollution. According to the Convention on Migratory Species Secretariat, “millions of birds” are killed every year as a direct result of the pollutant. 

“It alters the natural patterns of light and dark in ecosystems. It can change birds’ migration patterns, foraging behaviors and vocal communication,” the organization explains. “Attracted by artificial light at night, particularly when there is low cloud, fog, rain or when flying at lower altitudes, migrating birds become disorientated and may end up circling in illuminated areas.” That, the group noted, causes the birds to become exhausted or collide with buildings. 

Turtles

Light pollution harms both adult and hatchling sea turtles. Adult female sea turtles seek out dark beaches to lay their eggs, but they won’t come ashore to do so if there are too many lights.

“Evidence of sea turtle disorientation along Florida’s Atlantic and Gulf coasts can be heart-rending and grisly,” writes the National Fish and Wildlife Foundation in a blog post. “Hatchlings often leave confused, zig-zagging tracks in the sand before heading inland to be crushed on a nearby roadway. Gigantic adult females sometimes wind up in a resort’s swimming pool, or under the wheels of a vehicle.”

Moths

An article published in 2020 in the journal Insect Conservation and Diversity found that artificial light at night can disrupt reproduction, as well as larval and pupal development. However, while researchers identified “strong evidence for effects of artificial light on moth behavior and physiology,” they found “little rigorous, direct evidence” that light pollution impacts on individual moths would impact an entire population.

Bats

Experiments conducted by Bat Conservation International, a nonprofit dedicated to the mammal’s protection, showed that lesser horseshoe bats (which are nocturnal creatures) would alter their activities in a “dramatic” manner amid artificial nighttime illumination.

Are Plants Impacted by Light Pollution?

Plants do indeed see impacts from light pollution, according to Wilson. Plants photosynthesize, meaning they use sunlight to create energy and oxygen. But artificial light can alter their cycle, shortening the recovery periods they undergo following a period of growth or even creating flowers when they traditionally wouldn’t, she says — an issue that is particularly problematic in the early wintertime.

“They’re starting to bud and make flowers earlier in the year, so there’s this temporal mismatch,” Wilson says. And “all the other animals that usually come out around the same time, they’re now behind schedule because these plants are already doing this … so now you’re having this risk that these two species that depend on each other are no longer interacting.”

How Are Astronomical Studies Impacted by Light Pollution?

Looking up at the sky at night in a deeply dark area, you’re able to see many more stars and perhaps even other celestial bodies than you could in a densely populated area without technological assistance. That means that there are only a few places on Earth where excellent conditions exist for astronomical observation.

How Are Light Pollution and Energy Efficiency Connected?

Whenever you’re using too much of something or aren’t being careful with how you use it, inevitably there is waste. And leaving lights on all night or not directing them to the intended point results in quite a bit of inefficient energy use.

“You’re not wasting energy, so if you want to talk about financial savings, if you’re not producing that light, the [avoidable costs] merely go back into the community’s pocket,” says Wilson, citing the efforts of the city of Tucson, Arizona, which dimmed its street lights to 60% intensity after midnight. The Arizona Daily Star reported at the time that “the city estimated the conversion would cost about $16.5 million and would be paid back in savings over about 10 years.”

Across the U.S., the International Dark-Sky Association “estimates that at least 30% of all outdoor lighting” is wasted because of unshielded fixtures.

What Can I do to Reduce Light Pollution?

“If you turn a light off that’s not serving a task, it has an immediate and tangible impact — you are no longer providing that pollutant in the environment, it is gone,” says Wilson. “It’s not like water quality [or] agricultural runoff, that’s going to take decades to clean it all out and let the environment restore.”

You can educate yourself on the types of lights that avoid excessive cast or brightness and opt to purchase those. Or let manufacturers know that light fixtures designed with light pollution in mind is a product quality you care about. 

But in terms of long-term repair, Wilson said it’s hard to say how quickly — if at all — certain impacts on humans could be reversed, even if we all picked up better lighting habits.

“You still have accumulation from what you were exposed to previously … it’s not a single factor” says Wilson, noting the exposure to blue light from electronic devices. “ If we’re talking about [wildlife] communities and ecology, yeah, it’s gonna take them a while to come back and use that habitat if there was a lot of bright light that surpassed their tolerance.”