Light pollution: Environmental impact, health risks and facts

Light pollution seen from Pic du Midi de Bigorre Observatory
(Image credit: Getty Images)

Light pollution, or photo pollution, is the presence of excess artificial light and is the result of urbanization and industrialization. It is only one of the many forms of pollution on Earth, alongside plastic waste, greenhouse gases and sewage. 

Light pollution can have serious implications for our environment and even our health. Street lighting, domestic and commercial lights, vehicles and security lights all contribute to the creation of a dome-like shield of light pollution called skyglow, according to the International Dark-Sky Association (opens in new tab)

Along with skyglow, light pollution consists of glare, light trespass and clutter. Glare relates to light that can cause direct visual discomfort, whereas light trespass is light that escapes from sources such as bedroom windows. Clutter is the excessive grouping of lights. 

Light pollution can also be amplified by other types of air pollution, such as smoke and dust. This is because these types of pollution can scatter light in all different directions and brighten the sky even further.

Affects on astronomy and night vision

One of the immediate effects light pollution has on our environment is to obscure our view of the true night sky, according to telescope manufacturer Celestron (opens in new tab). Without the presence of artificial light, the night sky is awash with celestial bodies, far away galaxies and constellations. However, if you’re looking up from the belly of a big city, you’d be unable to see many of these night sky objects.

Around 99% of people living in Europe and America live under skies that are almost 10% brighter than they would naturally be, according to the BBC (opens in new tab). This also means that a large portion of the population doesn’t use the full potential of their eyes. 

The retina of the human eye can naturally adjust its light-sensing cells to acclimate to very low-light conditions, to allow some sort of night vision, according to the Duke University (opens in new tab). But because of light pollution, 37% of people living in America don’t use their night vision, according to the BBC. 

To monitor and characterise light pollution, American astronomer John E. Bortle created the Bortle Dark-Sky Scale (opens in new tab), which measures the brightness of the night sky at different locations. The scale measures our ability to observe celestial objects, such as planets and stars, under the interference of skyglow. 

Health risks

Other than depriving us of a starry star, there are many more implications to excess use of artificial light, such as throwing the human body's natural cycle out of whack.

Circadian rhythms are a group of physiological and neurological changes that occur in the body over a 24-hour-period. Collectively they’re also known as our body clock and is related to our sleep-wake cycle, according to Harvard University (opens in new tab)

Once the Sun has gone down and we are exposed to low light, our bodies naturally release a hormone called melatonin. Melatonin is released from the pineal gland in the brain and helps to increase tiredness and regulate sleep cycles, with peak production occurring in the early hours of the morning, according to the UK's National Heath Service (NHS) (opens in new tab)

However, light pollution has been found to curb melatonin production in humans, even at low levels. This can result in disturbed sleep, impact our immune system and responses to stress. It has also been suggested that melatonin disruption by way of light pollution is connected to the increased risk of hormone-related cancers, such as breast or prostate cancer, according to journal Environmental Health Perspectives (opens in new tab).  

The circadian rhythm doesn’t only affect humans, but most other living things. In studies of the European perch, researchers have found that even at the lowest light intensities disrupted melatonin production within the fish, according to the journal (opens in new tab) Environmental Pollution. 

Implications on wildlife behaviour

Along with health issues, light pollution can interfere with the behaviours of wildlife. Nocturnal predators such as bats are among the most affected by light pollution. These flying mammals are well adapted to hunting at night and actively avoid illuminated areas. 

Unfortunately, their insect prey is attracted to light sources, which leads to barren hunting grounds for bats, according to the Bat Conservation Trust (opens in new tab). Also, when sources of artificial light are placed outside a bat's roost, it can prevent them from ever leaving and lead to them starving. 

Bats flying through a city

Bats flying over Colorado river in Austin, Texas.  (Image credit: Getty Images)

While studying the reproductive cycle of wallabies, researchers have also found that births were weeks earlier among wallabies living near a lightly polluted area, such as a naval base, than those living in more rural areas, according to the Journal Proceedings of the Royal Society B (opens in new tab)

The study found that the use of outdoor light-emitting diodes (LEDs), which emit wavelengths in the blue spectrum of light, suppresses melatonin five times more than traditional outdoor light.

For newborn turtles, the presence of artificial lighting can make the difference between life and death, according to the Sea Turtle Conservancy (opens in new tab). As turtle hatchlings emerge along sandy beaches, their natural instinct is to scurry to the ocean bathed in moonlight. However, street and commercial lights along the coast can confuse the hatchlings and cause them to move inland where they are often eaten or killed by car traffic.

Additional resources

For more information about light pollution, check out "The End of Night: Searching for Natural Darkness in an Age of Artificial Light (opens in new tab)" by Paul Bogard and "Fighting Light Pollution: Smart Lighting Solutions for Individuals and Communities (opens in new tab)" by The International Dark-Sky Association. 

Bibliography

Scott Dutfield
Contributor

Scott is a staff writer for How It Works magazine and has previously written for other science and knowledge outlets, including BBC Wildlife magazine, World of Animals magazine, Space.com and All About History magazine. Scott has a masters in science and environmental journalism and a bachelor's degree in conservation biology degree from the University of Lincoln in the U.K. During his academic and professional career, Scott has participated in several animal conservation projects, including English bird surveys, wolf monitoring in Germany and leopard tracking in South Africa.