Show Mobile Navigation
Our World |

10 Ways That Light Pollution Harms The World

by Lance David LeClaire
fact checked by Jamie Frater

According to a 2001 report, two-thirds of the US and more than half of Europe can’t see the Milky Way with the naked eye. The culprit is light pollution—there are now so many artificial lights that they’re disrupting all sorts of lifeforms, including humanity. To make things even worse, some of the solutions might be more harmful than the problem, at least for us humans.

10Light Pollution Is Decimating Sea Turtles


Sea Turtles spend almost their entire lives in the ocean, but they do come ashore to lay their eggs in the sand. Then, when the young turtles hatch, they engage in a desperate scramble to reach the water before becoming a snack for various predators. But with hotels, restaurants, and houses taking up much of the world’s beachfront property, turtles are increasingly at risk on both occasions.

Female turtles looking for a place to lay their eggs won’t do so if the lights are too bright. If she fails to find a dark spot after several tries, the turtle will resort to suboptimal locations, and the young will have little chance to survive. The newborn turtles themselves make use of moonlight to guide them to the shore. Artificial light can turn them around, where they often wander right into the path of predators or cars. Thousands of young sea turtles are killed each year in Florida (which constitutes nearly 90 percent of America’s sea turtle nests) due to artificial lighting.

A program called the Sea Turtle Conservancy (STC) seeks to educate people on the need for proper lighting on beachfront property. If you live near a coast, STC recommends using yellow, amber, or red lights so as not to disturb turtle populations, as well as keeping lights low to the ground and shielded. As of 2014, STC and Florida authorities are working together on enforcing new rules requiring property owners to turn off or reposition lights while turtle season is in effect.

9It Disrupts The Breeding Cycles Of Amphibians


Wherever there are wetlands nearby, the nighttime chirping of frogs is one of the ubiquitous sounds of spring. But light pollution may one day make those voices go still.

Most amphibian species are nocturnal and water-dependent (even most toads have to go back to the water to breed). Because of this water-dependency, they have difficulty relocating in response to disruptions in their home areas. As nocturnal animals, they mark changing information in their environment by their photoperiods (the amount of time in a 24-hour period that they are exposed to sunlight). The photoperiod, which many animals use, is the only constant amphibians have to tell them when it is time to reproduce or hibernate and they are acutely sensitive to it.

Thanks to artificial light, many amphibians have demonstrated both physical and behavioral disruptions, including the disruption of their ability to know when to return home and breed. This means they miss the opportunity to reproduce. Many types of amphibians are currently facing population declines and light pollution is a big part of the problem.

8It’s Devastating To Bats


Bats feed on insect species that annoy and infect us, and are one of nature’s great sources of insect population control. But light pollution also effects them, to the point that populations are declining. Not all bat species are significantly impacted, but many species are extremely light-averse, and are repelled by streetlights and other artificial sources. Because insects are attracted to artificial light, which some bat species will not enter, bats lose many opportunities to feed. The situation is made even worse since the areas that the bats are willing to enter contain fewer insects than they normally would. This can disrupt entire bat colonies. Artificial lighting can also delay bats’ emergence from their roosts until well past dusk—an extremely important feeding time for most species.

A study in Britain, where it is illegal to kill or capture bats due to recent declines, has shown that in areas where important foraging habitats are artificially illuminated (especially through floodlighting) some species of bats won’t enter at all. This means that roads act as barriers to bat-crossing and woodland paths, rivers, and streams—where many insects gather at night—are denied to them. The problem is severe enough that the use of lighting on some properties may sometimes constitute a criminal offense unless British conservation authorities are consulted for advice.

7It Disrupts The Migratory Patterns Of Fish


Many fish migrate to spawn their young, often moving from oceans to lakes or along rivers. But studies have demonstrated that street lighting from nearby cities can disrupt these migratory patterns.

In 2012, a study compared a control group of Atlantic salmon smolts to a group under simulated artificial light conditions. The study found that for the control, migration occurred at sunset. But the second group migrated randomly, apparently confused by the lighting conditions. This can negatively impact fitness. In addition, since young salmon emerge at night in order to avoid predators, random changes in migration times result in more predation.

It gets worse—further studies have shown that public lighting, especially at night, can affect foraging, predation, shoaling, and reproductive success in general. Not only is this bad for marine ecology, it’s bad for the fishing industry, who don’t help themselves by using floodlit boats at night to attract fish species from miles around, often catching species they don’t want. Other species which are probably affected include trout and sea trout, barbell, graylings, eels, and lampreys.

6It Can Damage Trees


Have you ever walked through a city in the autumn and noticed a tree with no leaves except for where it faces a streetlight? The effect can be quite dramatic and the reason behind it is ominous. During the autumn season, many trees go into a period of dormancy to ride out the long winter months. That’s why trees shed leaves—to conserve as much energy as possible to survive the winter. They determine when to begin the process based on photoperiods. Night lighting (especially light along the red to infrared spectrums) effectively extends the day for many plants. Since angiosperms (flowering plants, including most trees) determine things like dormancy, flowering, and growth based upon the amount of uninterrupted darkness that falls upon them, this can have wide-ranging repercussions, including unsafe periods of non-dormancy.

Photoperiods also influence leaf shape, surface hairiness (pubescence), pigmentation, and root development, all of which impact fitness, and all of which can potentially be disrupted by light pollution. Of course, anything that impacts flowering plants also impacts pollinating insects. And since one third of our entire food supply depends on pollinators, it impacts all of us as well.

5Migrating Birds Are Lured To Their Deaths

9/11 WTC Tribute In Light Up-Close Showing Birds Trapped in the Lights

With the possible exception of our own health issues, no consequence of light pollution has attracted public attention more than the plight of birds. Many species of birds are nocturnal and migratory, dependent on the setting sun, the moon, and the night sky to navigate by. Bright lights at night can confuse birds into thinking they are flying towards these navigators instead of straight into a building. These collisions can kill the birds outright and even stunned birds often fall victim to predators. Researchers blame collisions with illuminated buildings for declines in songbird numbers—and a corresponding increase in scavengers such as rats and seagulls, which feed on the dead bodies.

How bad is it? Chicago’s Hancock Center has recently doused its night lighting in an effort to spare nearly 1,500 birds that are killed each night when they collide with the tower during migration season. Even more dramatically, on the first anniversary of the 9/11 attacks, New York commemorated the tragedy by shining two massive lights into the air where the World Trade Center once stood. The resulting swarm of thousands of birds trapped within the lights illuminated the problem for all to see.

4Artificial Light And Insects


Everyone has witnessed the familiar sight of a street or porch light swarming with insects at night, so much so that “like a moth to a flame” has come to mean an irresistible attraction. For insects, that is exactly what it is—many insect species are unstoppably drawn to artificial lights. Once within the light’s radius they find it difficult, if not impossible, to escape. This is because many insects, especially nocturnal ones, use natural light sources like the moon for navigation. Artificial lights confuse the cues they use to fly by.

Both normal flight activity and migratory patterns are disrupted, and insects are killed in great numbers by the heat of the lights or by predators who find an easy meal. These numbers are great enough to affect insect diversity—and if a species can’t reproduce fast enough, it may vanish from an area entirely.

There is another important problem associated with insects and light pollution—disease. Researchers believe that some disease-carrying species may have adapted to be attracted to artificial light as a cue that humans are in the area. Regardless, links have been established between light pollution and the spread of disease by insects such as mosquitoes (malaria, dengue, West Nile virus), sand flies (leishmaniasis), and kissing bugs (Chagas disease). In the case of mosquitoes, which are not usually attracted to light themselves, artificial lights allow people to stay outside later, thus exposing them during the mosquito’s most active period.

3It’s Making Our Minds Go Haywire


In 2011, researchers conducted a study on the effects of artificial lighting on mice—and their conclusions had ominous implications for us humans. Mice that were separated from the natural day/night cycle showed signs that their minds were going haywire. Mice kept on a 20-hour light cycle showed neurological alterations in emotional centers, grew to have difficulty navigating mazes, and were spooked by new environments. Their bodies also suffered, growing obese and developing altered levels of insulin and leptin, two metabolic hormones.

All living creatures, including humans, have an “internal clock” called the circadian rhythm, which is roughly structured to the natural 24-hour day. The amount of light present is conveyed to circadian systems by a pigment called melanopsin, which we now know is found in the human retina (until as recently as the 1980s, some scientists incorrectly believed that humans might be immune to the effects of the circadian cycle).

This natural rhythm tells our body many things: when to be wakeful, when to rest, when organs should be more active, when to eat, when to digest, and thousands of other instructions. Our moods, which are strongly affected by the production of hormones in our body, are also heavily influenced by our circadian cycle. And like the mice in the study, our minds and bodies are being negatively influenced by artificial lighting, with sleep disorders, behavioral problems, and mood disruptions becoming the order of the day. There are other psychological effects to consider as well. Many researchers and scientist believe that our reduced ability to experience the night and look up at the stars is having a negative effect on our internal well-being.

In 2013, another study suggested that indoor lighting is affecting the melatonin levels (another “timekeeper,” among other things) in our bodies, causing us to feel drowsy at inappropriate times. In an experiment, they sent groups of “early birds” and “night owls” to camp out with only sunlight and campfires for illumination. Both groups’ circadian rhythms quickly shifted to align with the sun. The researchers theorized that the morning drowsiness experienced by many is caused by indoor lighting interfering with this cycle. They recommend exposing yourself to natural lighting as much as possible and dimming unneeded houselights a few hours before sleep.

2It Can Wreck Our Physical Health As Well


It isn’t just our minds and moods that are at risk—light pollution has become such a pervasive human health issue that the American Medical Association (AMA) recently passed a resolution declaring it responsible for a host of physical problems. The resolution states that the increased amount of light in the world, including streetlight glare and ambient light “intruding” into windows, has links to breast cancer and depresses immune systems. It also has indirect health effects. Increased glare makes it harder to see, resulting in more traffic deaths at night. The AMA estimates that more than $10 billion a year could be saved if an effective program to reduce light pollution was implemented.

The Council of Europe has also stated that light pollution is linked to diabetes, depression, failure at school, and difficulties in concentrating, and we know that there is a link between artificial light and obesity as well. Artificial lighting has even been linked to a disruption in the development of the circadian system in newborn infants.

Breast cancer is perhaps the most dangerous health problem associated with light pollution. In 2001, a study found a strong link between women who had worked over 30 years of night shifts and an increased rate of the condition.

1LEDs May Be Making It Worse


Fortunately, more and more people are becoming aware of the wide range of problems caused by light pollution. Even better, it’s one of the environmental problems that could actually be tackled fairly easily. New energy-efficient LED technology is making it possible to replace inefficient street lighting with shaped, glare-less lights that have the potential to greatly reduce the impact on local wildlife. LEDs may cost more, but they last far longer than sodium lights, use a fraction of the energy of both sodium and incandescent lighting, and do not contain mercury like fluorescents. Their wavelengths are also far less disturbing for many species of wildlife. What’s not to like?

But the solution for animals may create an even bigger problem for us. Blue-rich LEDs increase the amount of light pollution the human eye is exposed to, increasing the risks mentioned in the previous two entries. The blue wavelengths of most LEDs mimic the light of the early-morning sun, signaling the brain that it should be waking up (so all those gadgets in your house are sending you exactly the wrong signals at night). Researchers writing for the Journal of Applied Ecology estimate that LED outdoor lighting could severely worsen the effects of light pollution. Most agree that effective light shielding, rather than a certain type of lighting, is our best option.

Lance LeClaire is a freelance artist and writer. He writes on subjects ranging from science and skepticism, atheism, and religious history and issues, to unexplained mysteries and historical oddities, among other subjects. You can look him up on Facebook, or keep an eye for his articles on Listverse.

fact checked by Jamie Frater