The International Dark-Sky Association defines light pollution as: “Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste."
Light trespass occurs when unwanted light enters one's property, for instance, your neighbor's security light that is not switched. Over-illumination is the excessive use of light. How many lights really need to be on in a skyscraper at night? Over-illumination wastes two million barrels of oil per day. (DOE stats) Glare is often the result of excessive contrast between bright and dark areas in the field of view. If you drive at night, you understand glare. Light clutter refers to excessive groupings of lights. Streetlight and sign lighting is often the culprit here. Finally, my pet peeve, sky glow, refers to the "glow" effect that can be seen over populated areas. It is the reflected light from all the pollution fixtures and practices listed above. The same effect (the Rayleigh effect) that makes the sky various shades of blue in the daytime will make the night sky various shades of gray/black. If the night sky is too light, too gray or white, then no stars can be seen. For astronomers, this is a real problem. As populations increase with urban and suburban sprawl, combined with cheap lighting and poor practices, more and more places are losing the stars, so to speak.
It is a common problem that few are aware of and yet, easy to eliminate. We simply must become more frugal and aware of the dangers of too much light. Lighting uses 25% of the world's energy, and one way to save energy and fiscal budgets is to turn out the lights.
Recently there was an article in the news stating the in the UK, the government will be paying women survivors of breast cancer if they worked at night. While some studies have shown an association between shift work and cancer, it is still under study. Mostly, it has to do with the hormones and chemicals, like melatonin, that our body uses or makes in the dark-at night. When the chemistry is off, diseases look for the chinks in the armor. Nighttime light pollution also affects people more directly. Night vision and visual acuity may deteriorate. Too much light gives some people migraines. The light itself is a subconscious reminder that people out there are moving, busying themselves in fun or work, and that knowledge can actually raise your blood pressure. Fatigue, stress, and even sexual dysfunction and infertility have all been tied to the health effects of light pollution. Even indoor fluorescent lighting can be considered light pollution, and it's effects have been documented in a number of studies.
Naturalists are concerned about how light pollution disrupts the natural cycles of light and dark and the negative effect on non-human animals is being documented worldwide. The artificial light disrupts animal navigation, changes predator-prey relationships, and alters the biochemistry of species. Here are some examples:
1) Studies suggest that light pollution around lakes prevents plankton, such as Daphnia, from eating surface algae, helping cause algal blooms that kill off plants and lower water quality.
2) Sea turtle hatchlings emerge from nests on beaches and move inland instead of out to sea. They don't really navigate by the moon, but they move to the lighter area by contrast. For millions of years, the dunes behind them were darker than the ocean before them. That is not true any longer. This is endangering to many species of turtles.
3) Migrating birds can be disoriented by lights on tall structures. Millions of birds are killed every year by flying into skyscrapers.
4) Night blooming flowers that depend on moths and nocturnal insects for pollination may be affected by night lighting. This can lead to species decline of plants that are unable to reproduce, and change the ecosystem.
5) Light pollution can negatively impact the migratory and breeding behaviour of frogs and salamanders, the canaries in the coalmine of our own world.
I wonder, too, if light pollution, especially sky glow, is responsible death of certain coral reefs.
The first thing you can do is to make yourself aware of your own situation. Globe at Night has easy charts so that you can compare the sky you see to what is really there. Between now and March 28th, people are observing the skies in their locations and then they will objectively report their location and the condition of the pollution. It is fun to participate. Hopefully it will open your eyes and make you aware of what you are missing. Once you have the facts, contact your local city council and try to get lighting changed or have special ordinances instated. You can do this!
In the meantime, participate in Earth Hour, which is on March 28. With observation and compliance, cities, corporations, and individuals around the world will collectively turn off the lights for one hour to save energy and protect the environment. Tell your neighbors and co-workers.
You can learn more here:
http://www.globe.gov/GaN/
http://www.globe.gov/GaN/observe_magnitude.html
http://www.darksky.org/mc/page.do
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