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WHEN THE LIGHT IS ON | The Unseen Effects of Light Pollution

More than a century ago, people from anywhere around the world could walk outside at night and have a spectacular view of the Milky Way arch. Nowadays, if you attempt to look at the stars, you may find that it is nearly impossible because our night skies are flooded with so much light that “light pollution” has become a real problem.


Figure 1/ Mt. Taranaki Milky Way by Larryn Rae, earthsky.org

Figure 2/ Milky Way Arch on New Mexico by Alan Dyer, amazingsky.net



The International Dark-Sky Association defines light pollution as the inappropriate or excessive use of artificial light. The sources of light pollution include exterior and interior lighting of buildings, advertising, commercial properties, offices, factories, streetlights, and illuminated athletic stadiums. Its main components are as follows:

  • Glare – a two-part problem in which lights are reflected off surrounding surfaces, scattering and causing vision problems. It does not impair night vision, but it can cause difficulties in identifying and placing objects. For example, car headlights beam brightly, especially at night, in locations where there are few other light sources. As a result, people living near high-traffic routes are vulnerable to disruptions caused by these bright, moving lights.

Photo by startrescue.co.uk

Skyglow – is a term used to describe the almost dome-like blanket of light that exists in urban areas. It’s the light emitted by streetlamps, signs, homes, and businesses that rise into the atmosphere, which changes the quality of light in the environment and then returns to the city from the atmosphere. This can also be a result of excessive light due to overpopulation because the more residents there are in an area, the higher lighting requirements and electrical consumption there are.

Photo by Thomas Davies, Cosmos Magazine

  • Light trespass – refers to an unwanted light invading someone’s property. It could be light from a sign coming into a residential neighborhood, or it could be anything similar. An example is a streetlight placed too close to houses which may disrupt people’s sleep.

Photo by Bob O’ Connor, IEEE Spectrum



Studies have shown that inappropriate light, or too much light, has adverse effects on one’s health and quality of life.

Circadian Rhythm and Melatonin

The circadian rhythm governs the human body’s cycles, as it does the other living things on the planet. Circadian rhythms are natural cycles of physical, mental, and behavioral changes that occur every 24 hours, and which are primarily influenced by light and dark.

According to Paolo Sassone-Corsi, chairman of the Pharmacology Department at the University of California, Irvine, and who has done extensive research on this subject, “The circadian cycle influences between 10% and 15% of our genes.” As a result, disruption of the circadian clock is linked to several medical disorders in humans, including depression, insomnia, cardiovascular disease, and cancer.

In response to the circadian system, our bodies create melatonin. Melatonin is a hormone that keeps us healthy. It has antioxidant effects, stimulates sleep, strengthens the immune system, decreases cholesterol, and aids the thyroid, pancreas, ovaries, testes, and adrenal glands in their functions. Exposure to artificial light at night suppresses melatonin production. Subsequently, this can lead to sleep disorders and other health problems.

Sleep Disorders

According to the National Institute of Health (NIH), a change in our clocks affects our ability to sleep and wake at optimal times and leads to a decrease in cognitive and physical skills. A good night’s sleep can help you lose weight, reduce stress, and prevent the onset of diabetes. The NIH believes that humans perform best when they sleep at night and act throughout the day.


Light pollution affects the atmosphere too.  Since huge amounts of electricity are used for nighttime illumination, this results in a high level of CO2 emissions and other harmful gases. The emission of large amounts of CO2 into the atmosphere contributes to accelerating climate change.


Light pollution can harm entire ecosystems. Since these ecosystems are usually quite sensitive to environmental changes, it would be hard to adapt to new conditions effectively. Because light pollution is a man-made effect that does not exist in nature on a large scale, this can negatively alter and cause disorder to the ecosystems.

Light pollution may also impact animals and plants that live near cities. This effect may be more severe in areas that have previously been uninhabited by people. Animals in these locations may be susceptible to changes in their natural habitat and may migrate to areas with less light pollution.


  • Only use lighting when and where it is needed
  • Properly shield all outdoor lights
  • Install motion detector lights and timer
  • Use warm lights instead of cold lights
  • Set parameters for the use of electronics at night

Today, light pollution has become a serious problem. Although it may not appear to be a prime concern compared to other issues, it has significant consequences for humans and the entire environmental system. The least we could do is contribute to reducing light pollution and take the necessary measures to help mitigate its negative impacts.