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What is


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For most of us, the natural light from the Moon and the stars has long been replaced by the glow of artificial lights. With an ever-growing use of nighttime lighting, often unnecessary and unjustified by actual needs, light pollution and its harmful consequences are increasing across the world.


The term light pollution refers to the excessive or inappropriate use of artificial light. Light at night can have many harmful consequences, not only on the visibility of the night sky, but also on wildlife, ecosystems, security and health.

In Canada, over 99% of the population lives in a place where the night sky is affected by light pollution.


Of this number, more than three-quarters cannot see the Milky Way and the thousands of stars that are normally visible to the naked eye.

Artificial light is so present in our cities that almost half of Canadians no longer experience dark conditions similar to a true night, completely changing our relationship with the night and that of the species that coexist with us.


In addition to affecting the visibility of the starry sky and our window to the Universe, artificial light at night has many adverse effects. Ecosystems, security, economy, health, scientific research, and aesthetics, the impacts of this unnecessary waste are now increasingly understood and well documented.


Reducing light pollution is a winning cause on many aspects.

Night sky

Astronomers both professional and amateur were the first to notice the effects of light pollution, with the disappearance of the stars. With an increasingly bright sky, the stars, nebulae, and galaxies drown in light and become invisible.


Many astronomical observatories are threatened today. The largest observatory in Canada, the David Dunlap Observatory, has even been forced to close its doors in recent years. The excessive glow of the Toronto area made imagery no longer possible there.

Skyglow is mainly caused by artificial light emitted towards the sky and near the horizon. Airborne particles (dust, aerosols, droplets) and gas molecules reflect and scatter light in all directions. Because it is more scattered by the atmosphere, blue light contributes to a greater extent to skyglow than yellow light. This means that white light needs to be avoided for nightly use since it includes all of the colours and is often rich in blue light. 


Deprived of the beauty of the starry sky and nocturnal landscapes, city dwellers must travel for hundreds of kilometers outside of urban centres to admire the Milky Way. In major cities around the world, more than 98% of the stars are no longer visible to the naked eye.

Biodiversity and environment

With the global rise of artificial light at night in both intensity and territory, many living species are increasingly affected by light pollution.


Some interactions are obvious, such as the fatal attraction of insects to light, resulting in the death of hundreds of insects by night for every streetlight. Other interactions are less visible, but possibly even more severe, such as the changes in the relationships between plants and pollinators or between prey and predators.


By changing the apparent length of day and night, artificial light desynchronizes the natural biological rhythms and hours of activity of both diurnal and nocturnal animals. The lunar cycle can become completely invisible and seasonal changes are altered, affecting foraging, reproduction or migration.

The effects of all these distortions have great repercussions on the ecosystems. Today, more and more research is allowing us to better understand the impacts on the environment. Whether it is with sea turtles, birds, insects, plants, fish, or the production of greenhouse gases for electricity, the impact of light pollution is felt in nature. One thing is clear: night is essential to life.


Good nighttime lighting makes it possible to see and be seen adequately, ensuring the safety of all those who must live and work at night. However, it is wrong to associate abundant lighting with increased safety or dimmer lighting with danger.


Studies have shown, for example, that different strategies to turn off or reduce road lighting had no significant impact on the number of nighttime collisions.

Lighting programs aimed at reducing crime in some major U.S. cities have been harshly criticized in their methodologies and practices. Serious and well-controlled studies have shown that there is no direct link between night lighting and crime.

Artificial lighting can create a false sense of security without actually increasing actual safety. Glare is one of the unfortunate and potentially dangerous consequences of intense or poorly directed light at night. Much like the glare caused by an oncoming vehicle with its high beam headlights, poorly designed lighting reduces visibility and thus increases the risk of accidents.

Human health

Like most life forms on Earth, humans have a circadian cycle. This cycle, which acts like a biological clock, guides a multitude of important processes inside our body. Melatonin, a hormone secreted during the night by a gland located in the brain, is the main director of all this coordination.

Thanks to medical research, we now know that artificial light at night will disrupt the secretion of this hormone, modify the sleep cycle, and negatively influence the immune system. It has also been shown that it is the blue component of light that disrupts the secretion of melatonin.

The World Health Organization officially recognizes that the disruption of the biological clock can lead to many health problems, ranging from insomnia to cancer, depression, diabetes, and obesity.

Therefore, it appears important to reduce the amount of artificial light in our sleeping environment and to limit intrusive light as much as possible to avoid these harmful effects on health. If necessary, use light with a warmer tint in the evening.


Just as the impacts of light pollution are multiple, the solutions to reduce this nuisance are just as varied.


Reducing light pollution is too often wrongly interpreted as eliminating lighting at night, which is in fact very far from reality: reducing light pollution is simply lighting more intelligently and efficiently.

To find out about solutions for reducing light pollution, see our LIGHTING sections:

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