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The Negative Effects of Light Pollution

Fear the dark no more


The Negative Effects of Light Pollution

Light pollution has environmental consequences for the planet, as well as health consequences for humans. Find out how to limit light pollution in your home.

Light pollution has environmental consequences for the planet, as well as health consequences for humans. Find out how to limit light pollution in your home.

In our primeval days, nocturnal carnivores prowled through the inky black of our nights. Early humans, unsurprisingly, developed an instinctual fear of the dark. Then, after a long dark age, we took what is widely heralded as our largest evolutionary leap—we learned to control fire.

Banishing the shadows

Yet our fear of what lurks in the shadows has persisted through time. In our modern age, criminals prowl through the dark alleys of our nights. So, in the name of safety, we flood our streets, parks, and homes with light. The latest cars sport ever brighter headlights. Indoors we bathe in the brightly lit screens of our televisions and computers.

It is all too easy to forget that our bright nights are artificial. But nature doesn’t forget—our bodies don’t forget—and so we pay the price for what is now known as light pollution.

Pied Piper of the night

The ecosystems of the natural world have evolved around the light of the sun, moon, and stars. Light pollution disorients and confuses animals who navigate via these natural light sources.

For example, sea turtles lay their eggs on beaches. When these eggs hatch at night, the hatchlings instinctually move away from the dark silhouette of the sand dunes toward the brighter horizon of the ocean. However, many coastal areas are now populated, and the artificial lights cause the baby turtles to go the wrong way, away from the ocean and often to their deaths.

In another example, migrating birds navigate through the sky by using the stars and moon. When flying over large cities, they are attracted by the bright lights below. Disoriented, they often collide with brightly lit buildings, or become trapped within the city and die from exhaustion. In Toronto these bird deaths prompted the city to initiate the Lights Out Toronto! campaign in 2006 that implored Torontonians to turn off unnecessary lights at night.

On a physiological level, studies have shown that light pollution hampers reproductive cycles and even lowers the immune system in animals. All creatures on this planet are in some way affected by too much artificial light—including us.

Too much of a good thing

In Canada we’re depressingly familiar with our lack of sunshine, leading to seasonal affective disorder (SAD) or vitamin D deficiency. But too much light at night is also damaging, increasing our risk of certain cancers.

The reason light at night can hurt us is rooted in our biological clock, known as the circadian rhythm. The circadian rhythm is an approximately 24-hour cycle that governs the biological processes of life on earth, including humans. It syncs with our outside environment to control the release of different hormones, including melatonin, which causes drowsiness and also suppresses cancer tumours.

When blue spectrum light enters our eyes, photosensitive ganglion cells in our retinas inhibit the pineal gland, the organ responsible for melatonin production. Thus, melatonin levels are typically high at night and low during the day. Melatonin secretion, however, is disrupted by even low levels of light.

Cancer epidemiologist Richard Stevens first made the connection in 1987 when he linked high breast cancer rates among women working the night shift with artificial lighting. Further studies on nurses and airline crews have supported his theory. For men, preliminary evidence suggests light at night increases prostate cancer risk as well.

Recent animal studies have identified the role of melatonin in suppressing cancer cells. For example, cancer tumours grafted onto rats grew significantly ? larger when perfused with melatonin-depleted blood. Other animal studies have even linked the disruption of the circadian rhythm to depression, weight gain, impulsivity, and slower thinking.

In 2007 this snowballing evidence prompted the American Cancer Society to add “shift work that involves circadian disruption” as a probable cause of cancer. But the risk goes beyond shift workers.

Especially in our over-illuminated cities, simply waking up at night could expose your retinas to light pollution. Our obsession with staring at screens also compounds late-night exposure to light. The latest trend is to use smartphones and tablets late into the night. The LED screens in these electronic devices emit light of the worst kind: blue spectrum light, which suppresses melatonin.

So how do you protect yourself from light pollution? For ideas on limiting light pollution, see the sidebar, “The light stops here.”

Illuminating the light pollution problem

The larger implications of light pollution extend beyond local ecosystems and physical health. With an estimated two-thirds of Earth’s population living under light-polluted skies, over-illumination is an international concern.

The energy waste alone, for example, interweaves with global issues such as climate change. In the United States approximately US$2 billion annually is lost on wasted lighting. In Canada the combined light pollution energy cost for the major cities of Toronto, Montreal, Calgary, and Vancouver is estimated to be well over $122 million.

Disturbing evidence has emerged showing that light pollution exacerbates air pollution. Each night, compounds called nitrate radicals break down polluting chemicals in the air that form smog and ozone. However, a recent study found that nighttime lights significantly slowed down this nightly cleansing.

But perhaps the most dismissed complaint of light pollution is also the most meaningful to future generations. Light pollution is the bane of astronomers who must now retreat to far-flung places such as Hawaii or Chile to observe the stars. Interesting stars and constellations are increasingly more difficult to see with the naked eye behind a veil of orange glow. Many children have never seen the Milky Way.

For centuries the stars were an integral part of our ancestors’ lives, guiding them through their travels and inspiring ancient mythology. When we gaze upon the heavens, we gain perspective on our existence and feel awe for the mystery of the universe. It would be a shame to lose that. a

The light stops here

Limit light pollution in your home and neighbourhood. Here’s how:

  1. Use a red night light. Light in the red spectrum does not suppress melatonin.
  2. Keep tech items (laptops, televisions, smartphones) out of your bedroom.
  3. If you wake up in the middle of the night, do not read or watch TV. Instead practise quiet meditation to lull yourself back to sleep.
  4. If you do shift work, create a completely dark environment for your sleeping periods and try to keep a regular schedule.
  5. Get blackout curtains for your windows.
  6. Ensure your outdoor light fixtures shine downward, not upward.
  7. Cut back on security lighting. If you live outside the city, crime rates are actually higher during the day. Plus, bright lights can actually create an unsafe environment by creating deep shadows and more glare.
  8. Avoid permanent landscape lighting. There is no good reason to illuminate your hedges at night.
  9. When purchasing a new vehicle, consider a model with standard halogen headlights rather than xenon, which can be extremely bright to oncoming traffic.


When our internal clocks are disrupted due to increased exposure to light pollution, we may have trouble sleeping. Melatonin can provide short-term relief of temporary insomnia. If you are considering taking melatonin, discuss it with your health care practitioner or the knowledgeable staff at your natural health retailer.



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