Multiple Impacts

Light pollution reduction is a win-win cause because in addition to the dark sky disappearance, there are many more negative consequences to nocturnal artificial lighting. Astronomy, economy, security, environment, health, aesthetics and heritage, impacts of this useless waste are more and more identified. 

Astronomy: Sky glow


Sky glow is one of the major effects of light pollution that disrupt astronomers work and denies citizens the beauty of dark starry skies and nightscapes. Today, one must unfortunately go a few hundred kilometers from urban centres to properly see the Milky Way. In fact, more that two third of Americans can no longer perceive the Milky Way with the naked eye from the place they live. In large cities of the world, nearly 97% of stars are no longer visible. For example, in Montreal, people can now see only about 100 stars but in the Mont-Mégantic International Dark Sky Reserve, it is possible to admire more that 3,000 stars with the naked eye.

Sky glow is caused by light artificially emitted into the sky, directly by luminaires, or after reflecting off the ground. Light emitted into the sky is made visible (and thus harmful) by reflection on particles in the air (dust, aerosols, humidity) or intrinsic diffusion of atmosphere. Blue light, because it is more diffused by atmosphere, contributes more to sky glow that yellow light.


For astronomers and astrophysicists, darkness of the sky is essential to the observation and study of celestial objects of faint luminosity. Light pollution’s significant expansion is affecting research activities in major observatories, because increase of the sky artificial lighting is having similar effect as telescope shrinkage. And that is why the largest observatory in Canada, David Dunlap Observatory, was forced to close its doors. Excessive luminosity from the Toronto sky was fatal and imagery had become impossible. In United States, observatories activities at Harvard University in Massachusetts and Mount Palomar in California, both located on the outskirts of large cities, are now compromised for the same reasons.

Impact of light pollution on the outskirts of Toronto is clearly visible in these 2 photos taken during and after the 2003 main power failure.

Economy: A waste of energy


In North America, energy spent to light needlessly the sky reaches each year close to two billion dollars. Besides this enormous useless expense, this energy is wasted and contributes to increase greenhouse-gas emission when electricity is produced by fossil fuels, which is usually the case.

In Québec, a geographic zone known to generate the most light per capita in the world, savings that could be gained with better lighting management are estimated at more than 700 GWh annually, which corresponds to energy used by approximately 20,000 electrically heated houses. All this waste costs over 50 millions dollars a year! With the conversion of light fixtures undertaken in the Mont-Mégantic International Dark Sky Reserve creation project, this would amount to 200,000 dollars savings per year for the area.

Security: Visibility and glare


Good nocturnal lighting allows us to see well and to be well seen, ensuring safety for all who live and work at night. However, it is wrong and harmful to associate intense lighting with security and faint lighting with danger. Thus, abusive lighting often comes from this widely spread belief!


It is widely accepted today that artificial lighting can contribute to create a false sense of security without really enhancing security itself. Badly designed lighting systems only serve to diminish visibility and increase accident risks! Studies have shown that:

  • Most robberies occur in broad day-light;
  • The number of accidents occurring at roadway intersections does not diminish with the increase of lighting;
  • In certain locations, a reduction of the number of accidents was recorded since switching-off road lighting;
  • There are few or no link between nocturnal lighting and criminality.

Finally, here is an example that shows that absence of nocturnal lighting does not encourage criminals: In the United States, many schools in Texas, Oregon and California have adopted a Dark Campus Program and banished nocturnal lighting outside regular activities hours. Contrary to the expectations of many people, there has been a marked decrease of acts of vandalism.


Human eye is able to see well under many various lighting conditions. For example, it is possible to see well in the light of a bright sunshine summer day and also under the soft light of a full moon. However, this adjustment of the eye is not achieved instantly. Adaptation to changes in light intensity is even slower with older people. When changes are quick and frequent, the eye is not able to adapt. Visual perception is therefore optimal when lighting is even.


Glare is one of the unfortunate effects of intense, uneven or badly directed lighting. Glare happens when eyes are submitted to a luminous glow that forces the pupil of the eye to close and creates an important contrast between the more luminous zones and those that are less. This phenomenon is often experienced when we come across an oncoming vehicle. Glare will considerably limit the capacity to distinguish oncoming obstacles, which could increase the risk of accidents. Glare sources are:


No matter what precautions are taken to reduce the impact, high power light bulbs are always a glare source as soon as part of the direct or reflected beam enters the eye. The two photos below illustrate important differences between good lighting and glaring light. In the picture on the left, taken in a small village, a store is lighted with very high power bulbs that emit light in all directions. Passersby and motorists are blinded by this chaotic light. The picture on the right shows how the situation was corrected with the use of new luminaires that better direct light and new lower power light bulbs.


Light reflected off highly illuminated surfaces is very intense and produces glare when adjacent to darker zones.  On the pictures below, a country road is lighted at an average level of 20 lux, which is three times more than the recommended use for this type of situation. The parts that are not lighted seem very dark in contrast with the road, and it becomes hard to see obstacles. It is also very hard to see the pedestrian who is walking towards the lighted zone. A more low-keyed and gradual lighting between the lighted zone and the dark zone would significantly improve visibility and security. 

Regardless the type of luminaire used or the luminous intensity, light emitted at less that 10° under the horizon line penetrates directly in the eye and causes glare. So, a luminaire should always be installed so that the light is reflected downward.



Living beings have always managed to take advantage of the benefits of a day as well as a night environment. Therefore, it is not surprising that light pollution, which directly translates as the disappearance of the night, may have adverse effects on this environment. Study of light pollution effects on fauna and flora is a fairly new science but biologists and ecologists have nevertheless reached consensus on the numerous negative impacts.


Whether on sea turtles, birds, insects, plants or greenhouse-gas emission, light pollution impact is felt in nature and one thing is clear: dark night is essential to life.

  • Young turtles which leave their nest use the natural glow of the sea and the moon to guide themselves and seek shelter in water. Artificial lights on sea shores confuse turtles and make them vulnerable to predators. Photo: wikipedia/Hila Shaked
  • Excessive light in large urban areas and lighted sea shores confuse the sense of orientation of migratory birds. Millions of them kill themselves on superstructures like bridges, buildings, etc. Photo: wikipedia/Charliebrown7034
  • Many insects, attracted by light, are killed directly by light bulbs that are not protected or are eaten by predators who thus can find them more easily. This causes imbalances in the food chain. Photo: flickr/Jörg Weingrill
  • Although plants use light to grow, they also need to rest at night. Many negative effects caused by artificial lighting have been observed on plants and algae. Photo: flickr/SeanJCPhoto
  • Indirect consequence of light pollution, production of this wasted energy results in the production of more greenhouse-gas effect. A recent study shows also that light pollution could jeopardize the natural reduction of smog during the night. Photo: flickr/Wigwam Jones

Health:  Biological clock and melatonin


It has been established scientifically by World Health Organization that biological clock disturbance may cause a range of health problems, from insomnia to cancer, depression, diabetes and obesity.


These disturbances are often related to an essential hormone disruption - melatonin – secreted during sleep, in complete absence of light. Regulatory hormone of the human body, melatonin coordinates production of other hormones, plays an important role in the immune system and has many antioxidant and anti tumoral properties.  It was discovered and demonstrated that nocturnal production of melatonin was suppressed by the presence of a small quantity of light, particularly blue light, which is produced for example by LED and metal halide light fixtures. 


Consequently, it would be important to reduce as far as possible the amount of light in our sleep environment and to limit as far as possible intrusive light in order to prevent disruption of our body’s biological rhythm, essential for our health.




Badly designed lighting will a have large impact on architectural or patrimonial aesthetics. Whether because of glare caused by visibly intense light sources, bad management of contrasts or colour selection, the beauty of a site or a building is strongly affected by lighting. Favouring fixtures with downward lighting, hidden under cornices for example, helps to highlight the whole of a building without blinding observers. Not only does warm colour lighting have less of an impact on light pollution, but it invites warmer feelings than white and blue lights.



In addition to the above mentioned multiple negative impacts of light pollution, one of the biggest losses is the loss of experiencing a dark starry sky. Millions of city dwellers today are deprived of the incredible vision of thousands of stars suspended in the sky, the Milky Way spreading from one horizon to the other, northern lights with magnificent colours...


Designated by UNESCO as "World Heritage", starry skies are today endangered and are fading away. Luckily for us, and unlike other environmental issues, it is possible to recover a darker sky and all its wonders by better controlling the way we light the night to reduce light pollution.