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This article is about light pollution in the visible spectrum. For information on pollution in the radio spectrum, see radio spectrum pollution.
This time exposure photo of New York City at night shows sky glow, one form of light pollution.
Comparison of the view of the night sky from a small rural town (top) and a metropolitan area (bottom). Light pollution vastly reduces the visibility of stars.
Light pollution in Szczecin, Poland
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light. The International Dark-Sky Association (IDA), "The Light Pollution Authority," 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.| ”| It obscures the stars in the night sky for city dwellers, interferes with astronomical observatories, and, like any other form of pollution, disrupts ecosystems and has adverse health effects. Light pollution can be divided into two main types: 1) annoying light that intrudes on an otherwise natural or low-light setting and 2) excessive light (generally indoors) that leads to discomfort and adverse health effects. Since the early 1980s, a global dark-sky movement has emerged, with concerned people campaigning to reduce the amount of light pollution. Light pollution is a side effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Japan and in major cities in the Middle East and North Africa like Cairo, but even relatively small amounts of light can be noticed and create problems. Like other forms of pollution (such as air, water, and noise pollution) light pollution causes damage to the environment. Contents[hide] * 1 Impact on energy usage * 2 Types * 2.1 Light trespass * 2.2 Over-illumination * 2.3 Glare * 2.4 Light clutter * 2.5 Skyglow * 3 Measurement and global effects * 4 Consequences * 4.1 Energy waste * 4.2 Effects on human health and psychology * 4.3 Disruption of ecosystems * 4.4 Effect on astronomy * 5 Reduction * 5.1 Improving lighting fixtures * 5.2 Adjusting types of light sources * 5.3 Re-designing lighting plans * 6 See also * 7 References * 8 External links * 8.1 Related organizations * 8.2 Research about light pollution * 8.3 Collections of links related to light pollution|  Impact on energy usage
Energy conservation advocates contend that light pollution must be addressed by changing the habits of society, so that lighting is used more efficiently, with less waste and less creation of unwanted or unneeded illumination. The case against light pollution is strengthened by a range of studies on health effects, suggesting that excess light may induce loss in visual acuity, hypertension, headaches and increased incidence of carcinoma. Several industry groups also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides its members information about light pollution, the problems it causes, and how to reduce its impact. Since not everyone is irritated by the same lighting sources, it is common for one person's light "pollution" to be light that is desirable for another. One example of this is found in advertising, when an advertiser wishes for particular lights to be bright and visible, even though others find them annoying. Other types of light pollution are more certain. For instance, light that accidentally crosses a property boundary and annoys a neighbor is...