When water is polluted it has things in it that are unhealthy or nasty, substances that don't belong there. Harmful gases or particles in the air make air pollution. But what do we mean by light pollution?
If artificial light is annoying, unnecessary, or damaging to other people or wildlife, we call it light pollution. One person's lighting shouldn't interfere with others.
The most obvious light pollution is in the sky above towns and cities. It glows a sort of orange color. This is the result of all the lighting which spills upward. It can often be seen from miles away. It's bright enough to hide the light from stars and other sights of the natural night sky.
Light pollution ruins astronomy.
Astronomers used to be able to observe from cities and towns. The first permanent mountain-top observatory wasn't built until 1887. Even observatories that once had dark skies are losing them. This is because cities keep spreading out. Most major observatories are now in places a long way from cities. Some older observatories have worked with their local communities to reduce the bad effects of outdoor lighting on the night sky. Others haven't had such cooperation.
Light pollution means everyone loses the sky.
The night sky was part of human life for tens of thousands of years. It was a storybook of gods and heroes, acted as clock and calendar, and showed the way before GPS, and was an inspiration for art and science. Yes, professional and amateur astronomers want to see the sky, but the view belongs to everyone.
Two-thirds of the people of the USA and half of those in the European Union can't see the Milky Way. Have you ever enjoyed seeing the night sky in a planetarium? Think what it would be like to see it outside your own window.
Light pollution damages wildlife.
Artificial light affects migratory animals. For example, birds that migrate at night use sky objects like the Moon to find their way. Bright artificial lights confuse them, so they often fly into brightly lit buildings or other structures. They may also get lost or circle around the light until they're exhausted and fall out of the sky.
Light disrupts the lives of any nocturnal species, creatures that are active at night. A nocturnal animal loses some of its habitat when there is no night. There is less food for them and they are in greater danger from their predators. Mating patterns get confused. The light doesn't just affect the cities, because the glow of the night sky goes on for miles beyond the city.
Light pollution affects people's health.
Animals and plants have daily rhythms based on daily changes of light and dark. Internal clocks, called circadian clocks, keep them going smoothly. But sky glow disturbs them.
People also have circadian clocks, and light disrupts them too. People affected by bright street lighting, a neighbor's “security” lights or lights from nearby buildings may sleep badly. Poor sleep patterns can cause stress, weight gain, depression, and serious illness.
The American Medical Association is concerned about the health problems caused by bad outdoor lighting. It supports partly covering the lights and directing them carefully. This would make sure the light only goes where it's needed, not up into the sky or into people's windows.
Light pollution is expensive.
We know that lots of light is being wasted. When you see night pictures of Earth from space, you can see that we're lighting the sky and not the ground.
Missouri State University studied the problem of unnecessary outdoor lighting in the USA. Unnecessary light spills over into other people's property, is brighter than it needs to be, is in the wrong place, shines upward or is wrong in some other way. It costs 6.9 billion dollars a year to produce the electricity for this wasted lighting. Producing the electricity also means using fossil fuels, which adds to air pollution and increases the carbon footprint.
In Calgary in Alberta, Canada they made changes to the street lighting. Besides reducing light pollution, they saved enough on electricity to cover the cost of making the changes.
International Dark Sky Week
In April, around the time of the new moon, International Dark Sky Week happens. This is a time to celebrate the night sky and help people to understand how light pollution threatens it. It grew out of National Dark Sky Week in the USA. The first one happened in 2003 because Jennifer Barlow, a 15-year-old Virginia school student, wanted to tell people about how we were losing something wonderful.
You can see pictures about this article on my Pinterest board “Endless Day”.
If you want to know more about why light pollution is a problem and how we can solve it, the Astronomy Forum has a link to the Dark-Sky Association.