What is Light Pollution and how does it impact Canadians?

Monday, May 7, 2018, 8:32 AM - Look up into the night sky. What do you see?

Does the spectacle of the Milky Way, with thousands of visible stars, stretch across your view, or do you see only a few pinpoints of light scattered on an otherwise dull blue-grey backdrop that stretches from horizon to horizon?

According to the new world atlas of artificial night sky brightness, released in 2016, less than one per cent of Canadians regularly experience the former - seeing the skies completely free of competing sources of light. So, based on this new atlas, what are the rest of us losing out on and why?

Although large areas of Canada's north are free from light pollution, our cities, strung across the southern parts of the country, light up the night sky. Credit: Falchi et al., Sci. Adv., Jakob Grothe/NPS contractor, Matthew Price/CIRES

Dark Skies

Look up into the sky during the day, and besides the Sun shining brightly, you may - if you look very closely - manage to pick out some other objects: The Moon, Venus, Jupiter, and possibly even an orbiting satellite if they catch the light just right. The rest of the universe is hidden from our view by the scattering of sunlight by Earth's atmosphere.

Look up into the sky at night, and you may expect to see much more - the expanse of the universe stretching from horizon to horizon. If you live in or near one of our nation's urban centres, however, that expanse has been taken away from you, little by little. Due to the light shed by our growing cities and towns, from street lamps, building lights, electronic signs, vehicles, etc, there is sometimes very little difference between what we see of the universe from day to night.

This can have an impact on our health, as the nighttime glow disrupts our circadian rhythms, it can have a detrimental effect on wildlife as well, and it robs us of the night sky.

Zooming in on the Detroit to Montreal corridor, one of the worst areas for urban light sources, shows the large contrasts of light pollution across southern Ontario and southwestern Quebec:

As shown in the video above, light pollution in the core of a large to moderately sized urban centre can completely wash out the night sky, but as one gets progressively further from these light sources, the view improves greatly.

The reason why this region is so bad for light pollution is due to the density of its urban centres. Each town, city and metropolis has its own concentration of light sources, but clustering all of these communities close together augments the overall effect on the night sky.

Fortunately, for many regions of Canada, where urban centres are farther apart, a stargazer typically only needs to travel a short distance out of their community to reduce the amount of light pollution spoiling the night sky.

From glare to sky glow

Although they are generally from the same source, there are different kinds of light pollution that affect us.

Lights that line streets, illuminate parks and keep building spaces lit are a direct nuisance to us. These spoil our night vision simply by shining directly in our line of sight. Even if you are standing at the side of a dark road, with no street lights or buildings around, pulling out a cellphone, turning on a flashlight or a passing car's headlights can quickly force your eyes back to daytime colour-vision mode, and it could take some time to adjust back to night vision.

The collective lights of an urban centre also have indirect impacts. Many city lights have been designed - either for maximum illumination potential or simply without consideration for the side effects - to not only emit light downward, towards the ground, where it's most useful to us, but also off to the sides and even upward into the sky. The portion that shines upward, and downward-directed light reflected from artificial concrete surfaces, is at the right wavelengths to be scattered by air molecules, which produces a diffuse glow over the city, known as sky glow.

Sky glow intensity is highly dependent on the weather. On an overcast night, clouds will reflect most, if not all of the light back down towards the ground. During humid weather, the water vapour in the air will also reflect a large portion of the city lights, increasing the amount of sky glow. Even on clear, dry nights, however, the reflection simply from the air molecules themselves can be enough to wash out the majority of the night sky.

Not the source, but the spillover

Although urban lights are the problem when it comes to light pollution, we wouldn't need to shut everything off to regain the night sky.

Some lights probably could be turned off. Drive down the streets and highways at night and there are many buildings with business signs that are still lit, even though everyone is gone home until the next day. While this is likely seen as a form of indirect advertising, turning these off - at least later at night until morning, when most people are asleep - could have a noticeable effect for light pollution. Reducing the number of lights left on overnight in office buildings would help as well.

Since the misdirected light - the portion that radiates off to the sides and upward - is the bigger, more pervasive issue here, however, we simply need better designs for our outdoor light fixtures. Street lights could be fitted with hoods that direct the light mostly downward, eliminating the spillover shining upward and reducing the amount of light reflected from the ground. Even billboards and electronic signs could be angled or structured to shine much of their light downward instead of straight out to the side.

Changing the types of lights we use can help as well, as long as we carefully consider all the impacts. LEDs - light emitting diodes - are gaining popularity and are coming down in price. These are quite desirable for their energy-saving qualities, however if we use the wrong kind of LEDs, we can actually make the problem of light pollution worse.

The best LEDs to use, to ensure that we can reduce light pollution and regain at least part of the night sky, are ones that are lower temperature, thus minimizing the amount of blue light, since that is the wavelength most efficiently scattered by the atmosphere.

What can we do about this?

The Royal Astronomical Society of Canada has an entire portion of their website devoted to light pollution abatement. Primarily, the ways that we can all help with this is to make the right choices when illuminating our own homes and property, to make elected officials aware of the problem and the potential solutions, and to ensure that these solutions are given proper consideration by urban planning committees. The simple fact that most methods of light pollution abatement are actually quite cost effective - using less energy for more light and/or focusing illumination to allow for lower wattage sources - may be enough to bring these methods into the spotlight.

Sources: Falchi et al./Sci. Adv | CIRES/University of Colorado Boulder | International Dark-Sky Association | Royal Astronomical Society of Canada