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Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, unappealing, or unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, and sky glow. A single offending light source often falls into more than one of these categories.


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.

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.

A more recent discussion (2009), written by Professor Steven Lockley, Harvard Medical School, can be found in the CfDS handbook "Blinded by the Light?". Chapter 4, "Human health implications of light pollution" states that "... light intrusion, even if dim, is likely to have measurable effects on sleep disruption and melatonin suppression. Even if these effects are relatively small from night to night, continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks".

The New York Academy of Sciences is hosting a 1 day meeting, 19 June, 2009 titled Circadian Disruption and Cancer. Moreover remember that 40 Danish women shift workers have this year(2009) been awarded compensation for breast cancer "caused" by shift work made possible by light at night - the commonest cause of light pollution.

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.

Lighting is responsible for one-fourth of all energy consumption worldwide and case studies have shown that several forms of over-illumination constitute energy wastage, including non-beneficial upward direction of night-time lighting. In 2007, Terna, the company responsible for managing electricity flow in Italy, reported a saving of 645.2 million kWh in electricity consumption during the daylight saving period from April to October. It attributes this saving to the delayed need for artificial lighting during the evenings.

In Australia, public lighting is the single largest source of local government's greenhouse gas emissions, typically accounting for 30 to 50% of their emissions. There are 1.94 million public lights—one for every 10 Australians—that annually cost A$210 million, use 1,035 GWh of electricity and are responsible for 1.15 million tonnes of CO2 emissions. Current public lighting in Australia, particularly for minor roads and streets, uses large amounts of energy and financial resources, while often failing to provide high quality lighting. There are many ways to improve lighting quality while reducing energy use and greenhouse gas emissions as well as lowering costs.

Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure, and some lighting design textbooks] use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light may include: increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety.

Common levels of fluorescent lighting in offices are sufficient to elevate blood pressure by about eight points. There is some evidence that lengthy daily exposure to moderately high lighting leads to diminished sexual performance.[citation needed] Specifically within the USA, there is evidence that levels of light in most office environments lead to increased stress as well as increased worker errors.

Several published studies also suggest a link between exposure to light at night and risk of breast cancer, due to suppression of the normal nocturnal production of melatonin.

As early as in 1978 Cohen et al. proposed that reduced production of the hormone melatonin might increase the risk of breast cancer and citing "environmental lighting" as a possible causal factor.

Since the early 1980s, a global dark-sky movement has emerged, with concerned people campaigning to reduce the amount of light pollution.

Evaluation of existing plans has determined that more efficient lighting plans are possible. Light pollution can be reduced by turning off unneeded outdoor lights, and only lighting stadiums when there are people inside. Timers are especially valuable for this purpose.

One example of a lighting plan assessment can be seen in a report originally commissioned by the Office of the Deputy Prime Minister in the United Kingdom, and now available through the Department for Communities and Local Government. The report details a plan to be implemented throughout the UK, for designing lighting schemes in the countryside, with a particular focus on preserving the environment.

India does not have a good report card so far as light pollution is concerned. Besides posing a health hazard and being harmful to nocturnal life forms, light pollution also deprives urban dwellers of a chance to view the night sky lit up by stars.

Air and water pollution have a more immediate impact on human health. However, by paying attention to light pollution we would also be addressing the possibility of a more efficient use of energy for outdoor lighting that in turn will address the issue of diminishing energy resources, says N. Rathnasree, Director, Nehru Planetarium. She is studying levels of light pollution in India.

She says, “Some of the damage can be reversed with timely action. Knowing the pollution level quantitatively might also help us fight it better. The extent of light pollution can be studied through satellite imagery. However, translating from there to the question of actual sky brightness as seen from the ground involves a lot of estimation of unknown factors like aerosol content over different regions.”