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All About Light Pollution

by Chris Johnson - December 2012

When an otherwise natural area is contaminated with something that is harmful to it, it becomes polluted. The item introduced may be certain substances or factors. For example, most often when people think of pollution they think of the pollution in the air or water by chemicals. There are other types of pollution, however, such as pollution caused by light. Light pollution, also known as luminous pollution, is defined as the excessive introduction of artificial lighting to the outdoor environment. People who are unfamiliar with this problem often do not fully understand how light can become a pollutant. Around the world, street lights, stadium, park, and other lighting are illuminating the sky to such a magnitude that it creates a number of problems that are detrimental in terms of energy use, the environment and even to people. While light serves an undeniably important purpose, understanding light pollution can help people reduce its negative impact.

Types of Light Pollution

Light pollution falls into several different categories, or types. Each of these types illustrates a different way in which light spreads and, as a result, affects the surrounding environment. The different types of light pollution are sky glow, glare, light trespass, and clutter. Sky glow, which is frequently referred to as urban sky glow, occurs when artificial light projects upward and brightens the sky over an area. The glow seen over a city at night is an example of sky glow. Light trespass is when light from one area spills, or trespasses, onto another area where it was not intended to be. Glare is excessive brightness that comes from a light that is visually uncomfortable. In some cases, glare may also be disabling in that it reduces visibility. Clutter, in terms of light pollution, means large groupings, or clutters, of bright lighting. Light clutter can be distracting and confusing, and as a result it may prove dangerous to both aircraft pilots and drivers. Over illumination is yet another type of light pollution. This is the use of lighting beyond what is necessary. Empty parking lots with lights on are an example of over illumination.

Energy Usage Impact

Light pollution not only affects the sky, but it also wastes a significant amount of energy. According to the U.S. Energy Information Administration, 13% of the electricity use in the U.S. goes toward lighting in residential and commercial areas alone. Some studies show that one-third of the light that is used is wasted light. As a result, the energy that is used is also wasted. This comes at an estimated cost of approximately $2 billion a year.


The excess of artificial lighting comes with many negative side effects for both human beings and nature. Blocking the view to the stars is one of the more apparent negative aspects of light pollution. When the light from cities shines upward, it is reflected back by airborne dust, air molecules, and droplets of water vapor. This makes it increasingly difficult to see the stars and their constellations. This is most noticeable by astronomers and amateur star-gazer.

The behavior of certain animals is greatly affected by light pollution. Insects, for example, often fly toward light. At night, the position of the stars helps migrating birds to find their way. If the stars are not visible, the birds may become confused. Bright lights may also confuse birds, causing them to fly towards the light. This can result in unnecessary impact with other birds or buildings. When insects gravitate towards light, they become prey to animals, such as bats. Plant life may also be affected by excess illumination. Certain plants may require pollination from nocturnal insects, but light pollution may give off enough light that it interferes with the act. Some trees are sensitive to the length of the day and may be affected by night lighting, as well. Additionally, it affects the ecosystem and the life cycle of organisms within it.

Light pollution is also thought to affect human health. For instance, light pollution is known to disrupt circadian rhythms. This is a person's internal clock, which regulates 24 hour biological functions in the body. Interference with the circadian rhythm can hinder things such as the production of melatonin, which is believed to help prevent cancer. Metabolism is also affected and can cause problems such as obesity and diabetes.


Reducing light pollution requires the effort of both residents and city officials. Everyone must make efforts to reduce the amount and type of artificial light that is used at night. Motion-sensing lighting can help reduce over-illumination by only turning on lights when they are needed. Less lighting can be used to illuminate an area, and the intensity of lights may also be reduced. Using shielded lighting helps in several key ways, such as controlling light from traveling upward and reducing light trespass and glare. Current city lighting plans should also be reevaluated and updated more efficiently.

Image courtesy of NASA's Astronomy Picture of the Day from November 27, 2000.

Written by Chris Johnson

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