Spectacular night sky in Canyonlands National Park in Utah. It has Gold-Tier International Dark Sky Park status from the International Dark-Sky Association (IDA). For many visitors it's the first time they've ever seen the Milky Way. [Photo: Dan Duriscoe]

What is light pollution?
Light pollution is light where it isn't needed or wanted, including inappropriate lighting. It's not just the orange glow of an urban sky, but also the local effects of the bad lighting that add up to create this glow.

The night sky, our heritage
Urban skyglow chased professional astronomy away to the mountains long ago. But there are many more people who are amateur astronomers, as well as adults and children who would simply enjoy seeing the night sky. Martin Rees, the Astronomer Royal of England, makes the point well:

It's not just astronomers who want to experience a clear view of the stars, just as it's not just keen ornithologists who would feel deprived if song-birds disappeared from parks and gardens. It's . . . a deprivation if young people living in cities never see a dark starry sky - just as it is if they never see any natural countryside.

The night sky has been part of humanity's environment for thousands of years. It's how we found our way, the storybook of our myths and legends, the inspiration of poets, the beginning of science, and one of the nature's greatest art works. The night sky is our heritage and should be our children's. Yet the 2001 World Atlas of the Artificial Night Sky Brightness showed that, on average, 21% of the world's population couldn't see the Milky Way. The United Kingdom was the worst offender - the Milky Way is invisible to 55% of the inhabitants.

Wildlife
Light pollution also worries wildlife organizations including United Nations Environment Program overseeing the treaty on the Conservation of Migratory Species. The organization's secretariat has said that “legislation needs to be developed to support and require dark sky friendly lighting through by-laws, modified engineering standards and building codes.”

Many species, migratory or not, are affected. For example, birds that migrate at night are adapted to using celestial objects to help orient themselves. Bright artificial lights confuse them. Besides colliding with brightly lit structures, they often get lost or circle the light until they're exhausted.

But any nocturnal species effectively loses its habitat when there is no night. Mating patterns are disrupted, food sources diminished and they themselves are more vulnerable to predators. And it isn't just those living in cities. Sky glow extends for miles beyond the city, and towns in country areas are also guilty of lighting up the sky.

Health and safety
Animals also have daily rhythms based on alternating light and dark. They're known as circadian clocks, and sky glow disrupts them. People have circadian clocks too, and the hormone melatonin helps keep them regulated. Melatonin is only released when it's dark, because light inhibits it.

Shift working and jet travel disrupt our natural rhythms, but so can light at night. Intrusive street lighting, a neighbor's “security” lights and lighting from nearby buildings can be dangerous to your health. Sleep patterns are affected, and it can contribute to stress, weight gain, depression, weakening of your immune and serious illness. The American Medical Association has officially supported the general use of shielded outdoor lighting on health grounds.

Shielding directs the light to where it's supposed to go, not up into the sky or into people's windows. Since lower wattage bulbs are used with shielding, it also eliminates glare and reduces running costs.

Studies of the effect of lighting on crime have failed to show that lighting reduces crime. Much "security" lighting is inappropriate so that it doesn't do any good. It can even have the opposite effect if it's too bright, as that creates both glare and deep shadows that can hide intruders. In any case, most crimes are committed during the day or in lighted areas. One set of studies did show a big drop in crime following the installation of night lighting. Oddly, there was a decrease during the day too, making it obvious that there was something at work other than new lights.

Light pollution costs the Earth
We know that light is being wasted on a grand scale. You only need to see pictures from space to know that we're lighting the sky instead of the ground. A study at Missouri State University found that 30 per cent of the electricity produced for outdoor lighting in the USA was wasted. It cost $6.9 billion a year to produce. Generating the wasted electricity also involves squandering fossil fuels, adding to environmental pollution and increasing the carbon footprint.

In times of weak economies and cuts to public services, it's amazing that so much money can be wasted in creating a nuisance. In Calgary in Alberta, Canada the savings in running costs of street lighting over a decade paid for the costs of retrofitting the lights with shielding, and energy-saving bulbs.