Light pollution, as defined by the National Park Service (NPS), is any illumination of the night sky caused obtrusive artificial light. The problem began with the light bulb, an invention developed out of necessity about 125 years ago. It has become a burgeoning environmental challenge. Most light pollution is a result of urbanization and poorly designed fixtures. The NPS says much of the lighting that causes light pollution is unnecessary, including streetlights, stadium lights and billboards. Many researchers feel the same. “We’ve lit up the night as if it were an unoccupied country…,” Verlyn Klinkenborg writes in “Our Vanishing Night,” an article about light pollution recently featured in National Geographic.
The effects of light pollution are far reaching. According to “The First World Atlas of the Artificial Night Sky Brightness,” a paper published by the Monthly Notices of the Royal Astronomical Society, two-thirds of U.S inhabitants can no longer see the starry swath of the Milky Way. Roughly one-half of the people living the European Union cannot see it either. Light pollution isn’t limited to stars; it affects feeding, migration and reproduction too. The prolonged days upset natural sleeping, waking and feeding patterns. Klinkenborg describes how longer days prompted a swan population in England to put on winter weight quicker than normal. The birds would migrate sooner than usual, which would hinder nesting.
There are several causes of light pollution, including over illumination, sky glow, glare, clutter and light trespass. Over illumination is the use of artificial light beyond its specified purpose. It is excessive, for example, leaving workplace lights on after hours. Sky glow is the haze that appears above cities at night. Sky glow is the result of artificial light being projected upwards then scattered in the atmosphere, and it prevents stargazing. Glare is light that impairs vision. Some forms of glare produce high contrast shadows. For instance, an unshielded filament creates bright and dark spots within a viewer’s field of vision. Other forms of glare reduce contrast as in the case of light scattering in the fog and reflecting back. Clutter applies to groups of lights or those in too close proximity. Billboards or outdoor signs are examples of clutter, and they are considered distracting. Light trespass happens as unwanted light illuminates otherwise dark areas. It occurs when a security light shines in a neighboring home.
The good news is that light pollution can be managed. Cities and towns are enacting ordinances to reduce light trespass. Developers are working on utilizing energy efficient lighting and fixtures. Advocacy groups, such as the International Dark Sky Association and The British Astronomical Association's Campaign for Dark Skies, are educating the public about light pollution.
Sources:
http://www.nps.gov/grba/naturescience/lightscape.htm
http://ngm.nationalgeographic.com/2008/11/light-pollution/klinkenborg-text
http://science.nasa.gov/headlines/y2001/ast01nov_1.htm
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2627884
http://www.prairieastronomyclub.org/light.htm
http://www.savethenight.eu/Light%20Pollution%20in%20Europe.html