Light pollution is the alteration of the natural patterns of light and dark in ecosystems, resulting from the unnecessary and inefficient use of artificial lighting. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, and skyglow. A single offending light source often falls into more than one of these categories. Although this type of pollution can exist throughout the day, its effects are magnified during the night with the contrast of the sky's darkness. It has been estimated that 83% of the world's people live under light-polluted skies and that 23% of the world's land area is affected by skyglow. The area affected by artificial illumination continues to increase. A major side effect of urbanization, light pollution is blamed for compromising health, disrupting ecosystems, and spoiling aesthetic environments. Studies show that urban areas are more at risk. Globally, it has increased by at least 49% from 1992 to 2017, and between 2014 and 2022 by 16%, with uneven development, e.g. France reducing through policy its light pollution by 33% in that time period. Solutions to light pollution are often steps like adjusting light fixtures or using more appropriate light bulbs. Further remediation can be done with more efforts to educate the public in order to push legislative change. However, because it is a man-made phenomenon, addressing its impacts on humans and the environment has political, social, and economic considerations.
Definitions Light pollution is the presence of artificial light in otherwise dark conditions. The term is most commonly used in relation to in the outdoor environment and surrounding, but is also used to refer to artificial light indoors. Adverse consequences are multiple; some of them may not be known yet. Light pollution makes it harder for people in cities that use excessive artificial light and, like other pollutants, it can harm our environment. Light pollution is a side-effect of industrial civilization. Its sources include building exterior and interior lighting, advertising, outdoor area lighting (such as car parks), offices, factories, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Asia and in major cities in the Middle East and North Africa like Tehran and Cairo, but even relatively small amounts of light can be noticed and create problems. Awareness of the harmful effects of light pollution began in the second half of the 19th century, but efforts to address its effects did not begin until the 1950s. In the 1980s a global dark-sky movement emerged with the founding of the International Dark-Sky Association (now DarkSky International). There are now such educational and advocacy organizations in many countries worldwide. About 83% of people, including 99% of Europeans and Americans, live under light-polluted skies that are more than 10% brighter than natural darkness. 80% of North Americans cannot see the Milky Way galaxy.
Types
Light trespass Light trespass occurs when unwanted light enters one's property. A common light trespass problem occurs when a strong light enters the window of one's home from the outside, causing problems such as sleep deprivation. A number of cities in the U.S. have developed standards for outdoor lighting to protect the rights of their citizens against light trespass. DarkSky International was started to reduce the light going up into the sky which reduces the visibility of stars (see Skyglow below). This is any light that is emitted more than 90° above nadir. By limiting light at this 90° mark they have also reduced the light output in the 80–90° range which creates most of the light trespass issues.
U.S. federal agencies may also enforce standards and process complaints within their areas of jurisdiction. For instance, in the case of light trespass by white strobe lighting from communication towers in excess of FAA minimum lighting requirements the Federal Communications Commission maintains an Antenna Structure Registration database information which citizens may use to identify offending structures and provides a mechanism for processing citizen inquiries and complaints. The U.S. Green Building Council (USGBC) has also incorporated a credit for reducing the amount of light trespass and sky glow into their environmentally friendly building standard known as LEED. Light trespass can be reduced by selecting light fixtures that limit the amount of light emitted more than 80° above the nadir. The IESNA definitions include full cutoff (0%), cutoff (10%), and semi-cutoff (20%). (These definitions also include limits on light emitted above 90° to reduce sky glow.)
Over-illumination Over-illumination is the excessive and unnecessary use of light. A large and overabundant amount of electricity is required to support light consumption in the United States. U.S homes consumed 81 billion kilowatt hours (kWh) of electricity for lighting in 2020 according to the U.S. Energy Information Administration (EIA). Additionally, the EIA reported that 208 billion kWh and 53 billion kWh of electricity were used for commercial and manufacturing buildings respectively in 2018. Light use is not excessive in all developed countries. Amongst developed countries there are large variations in patterns of light use. American cities emit three to five times more light to space per capita compared to German cities. Over-illumination stems from several factors:
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