Light Pollution Defined

When most people think of pollution, physical substances like toxic liquids, poisonous gasses, and garbage litter are usually among the first things that come to mind. Contamination of the natural world, though, is not limited to such classic poisoners of the land, air, and sea. Pollution can come in the form of energy as well, including noise, heat, and artificial light. How can light be a pollutant, one may ask, when it is a necessity for nearly all forms of life on this planet? This is a fair and understandable question, as the very concept of light as a pollutant is rather counterintuitive. Nontheless, light pollution is a very real phenomenon, and one that is yielding notable, often detrimental consequences for species and ecosystems all over the world.

Global Use of Artificial Light at Night
 http://upload.wikimedia.org/wikipedia/commons/3/33/Terre-lumieres_de_nuit.jpg

 Light pollution refers specifically to artificial, man-made light. Such light, while obviously useful for humans in countless ways, becomes polluting when it is introduced into the environment. Its presence in a given system alters not only the natural light levels of the system, but also the natural light patterns. The two main variables here, in essence, are light intensity and timing (Longcore and Rich).

Urban Sky Glow
http://upload.wikimedia.org/wikipedia/commons/f/fe/M%C3%A9xico_City_at_Night_2005.jpg

While light pollution comes in many forms, there are two main types that yield ecological consequences: glare and sky glow. Glare refers to the direct shining of light, while sky glow refers to the general brightening of the night sky from artificial light introduced to the atmosphere (National Parks Service).