Light pollution

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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 shows sky glow, one form of light pollution. Glow reflected from background clouds demonstrates the upward-directed light, partly caused by unshielded lights.

Light pollution is excess or obtrusive light created by humans. Among other effects, it can cause adverse health effects, obscures stars to city dwellers, interferes with astronomical observatories, wastes energy and disrupts ecosystems. Light pollution can be construed to have two main branches: (a) annoying light that intrudes on an otherwise natural or low light setting and (b) excessive light, generally indoors, that leads to worker 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. It comes from sources such as building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and lit sporting venues. It is most severe in the highly industrialized, densely populated areas of the United States, Europe, and Japan, but even relatively small amounts of light can be noticed and create problems.

With recent advances in private spaceflight, the prospect of space-based orbiting billboards appearing in the near future has provoked concern that such objects may become another form of light pollution. With this in mind, the United States Federal Aviation Administration sought permission, in May 2005, to enforce a law prohibiting "obtrusive" advertising in earth orbit ^{[1] [2]}. Similar intentions are yet to be expressed by authorities in most other countries, however.

[edit] Light pollution as a problem

"Light pollution" (also known as photopollution, luminous pollution) refers to light that people find annoying, wasteful or harmful. It also does a lot of damage to the environment and health, as do other forms of pollution such as air pollution, water pollution and soil contamination.

Many people wish to reduce light pollution. However, it is unrealistic to expect populations to significantly reduce their light pollution, due to industrial society's economic reliance on artificial light. Detractors posit that light pollution is a problem similar to traditional forms of 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.

Several industry groups also recognize light pollution as an important issue. For example, the Institution of Lighting Engineers in the United Kingdom provides information for its members about light pollution, the problems it causes, and how to reduce its impacts[1].

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 generally wasted and pollutive light.

Disputes are still common when deciding appropriate action, and differences in opinion over what light is considered reasonable, and who should be responsible, mean that negotiation must sometimes take place between parties. Where objective measurement is desired, light levels can be quantified by field measurement or mathematical modeling, with results typically displayed as an isophote map or light contour map. Authorities have also taken a variety of measures for dealing with light pollution, depending on the interests, beliefs and understandings of the society involved. Measures range from doing nothing at all, to implementing strict laws and regulations about how lights may be installed and used.

[edit] Types of light pollution

Light pollution is a broad term that refers to multiple problems, all of which are caused by inefficient, annoying or arguably unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, clutter, and sky glow. It is common, however, for annoying or wasteful light to fit several of these categories.

[edit] Light trespass

Light trespass occurs when unwanted light enters one's property, for instance, by shining over a neighbor’s fence. A common light trespass problem occurs when a strong light enters the window of one's home from outside, causing problems such as sleep deprivation or the blocking of an evening view.

Light is particularly annoying for amateur astronomers, whose ability to observe the night sky from their property is likely to be inhibited by any stray light from nearby. Most major optical astronomical observatories are surrounded by zones of strictly-enforced restrictions on light emissions.

A number of cities in the U.S. have developed standards for outdoor lighting to protect the rights of their citizens against light tresspass. To assist them the International Dark-Sky Association has developed a set of model lighting ordinances. U.S. federal agencies may also enforce standards and process complaints within their areas of jursidiction. For instance, in the case of light tresspass by white strobe lighting from communication towers in excess of FAA minimum lighting requirements the FCC maintains a database of Antenna Structure Registration information and provides a mechanism for processing inquiries and complaints.

[edit] Over-illumination

Main article: Over-illumination

Over-illumination is the excessive use of light. Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wasted. This is based upon U.S. consumption of equivalent of 50 million barrels per day of petroleum [2], noting that 60% of U.S. supply is from natural gas, hydroelectric and other non-petroleum sources. Equivalent barrels per day of petroleum is simply an easy to visualize representation of energy use from all sources. It is further noted in the same U.S. Department of Energy source that over 30 percent of all energy is consumed by commercial, industrial and residential sectors. Energy audits of existing buildings demonstrate that the lighting component of residential, commercial and industrial uses consumes about 20 to 40 percent of those land uses, variable with region and land use. (Residential use lighting consumes only 10 to 30 percent of the energy bill while commercial buildings major use is lighting[3].) Thus lighting energy accounts for about four or five million barrels of oil (equivalent) per day. Again energy audit data demonstrates that about 30 to 60 percent^[3] of energy consumed in lighting is unneeded or gratuitous.

An alternative calculation starts with the fact that commercial building lighting consumes in excess of 81.68 terawatts (1999 data) of electricity [4], according to the U.S. DOE. Thus commercial lighting alone consumes about four to five million barrels per day (equivalent) of petroleum, in line with the alternate rationale above to estimate U.S. lighting energy consumption.

Over-illumination stems from several factors:

• Not using timers, occupancy sensors or other controls to extinguish lighting when not needed.
• Improper design, especially of workplace spaces, by specifying higher levels of light than needed for a given task.
• Incorrect choice of fixtures or light bulbs, which do not direct light into areas as needed .
• Improper selection of hardware to utilize more energy than needed to accomplish the lighting task.
• Incomplete training of building managers and occupants to use lighting systems efficiently.
• Inadequate lighting maintenance resulting in increased stray light and energy costs.

Most of these issues can be readily corrected with available, inexpensive technology; however, there is considerable inertia in the field of lighting design and with landlord/tenant practices that create barriers to rapid correction of these matters. Most importantly public awareness would need to improve for industrialized countries to realize the large payoff in reducing over-illumination.

[edit] Glare

Glare is the result of excessive contrast between bright and dark areas in the field of view. For example, glare can be associated with directly viewing the filament of an unshielded or badly shielded light. Light shining into the eyes of pedestrians and drivers can obscure night vision for up to an hour after exposure. Caused by high contrast between light and dark areas, glare can also make it difficult for the human eye to adjust to the differences in brightness. Glare is particularly an issue in road safety, as bright and/or badly shielded lights around roads may partially blind drivers or pedestrians unexpectedly, and contribute to accidents.

Glare can be categorized into different types. One such classification has been developed by Bob Mizon, coordinator for the British Astronomical Association's Campaign for Dark Skies^[4]. According to Mizon's classification:

• Blinding Glare describes effects such as that caused by staring into the Sun. It is completely blinding and leaves temporary vision deficiencies.
• Disability Glare describes effects such as being blinded by an oncoming cars lights, with significant reduction in sight capabilities.
• Discomfort Glare does not typically cause a dangerous situation in itself, and is annoying and irritating at best. It can potentially cause fatigue if experienced over extended periods.

[edit] Clutter

Clutter refers to excessive groupings of lights. Groupings of lights may generate confusion, distract from obstacles, including those that they may be intended to illuminate, and potentially cause accidents. Clutter is particularly noticeable on roads where the street lights are badly designed, or where brightly lit advertising surrounds the roadways. Depending on the motives of the person or organization who installed the lights, their placement and design may even be intended to distract drivers, and can contribute to accidents. Clutter may also present a hazard in the aviation environment if aviation safety lighting must compete for pilot attention with non-relevent lighting. For instance runway lighting may be confused with a dazzling array of suburban commercial lighting and aircraft collision avoidance lights may be confused with ground lights.

[edit] Sky glow

Los Angeles at night, with a brightly illuminated sky.

Main article: Sky glow

Sky glow refers to the "glow" effect that can be seen over populated areas. It is the combination of light reflected from what it has illuminated and from all of the badly directed light in that area, being refracted in the surrounding atmosphere. This refraction is strongly related to the wavelength of the light. Rayleigh scattering, which makes the sky appear blue in the daytime, also affects light that comes from the earth into the sky and is then redirected to become sky-glow, seen from the ground. As a result, blue light contributes significantly more to sky-glow than an equal amount of yellow light. Sky glow is of particular irritation to astronomers, because it reduces contrast in the night sky to the extent where it may even become impossible to see the brightest stars.

Astronomers begun to use the Bortle Dark-Sky Scale, to quantify sky glow, since it was published in Sky & Telescope magazine.^[5] The Bortle Scale rates the darkness of the sky, inhibited by sky glow, on a scale of one to nine, providing a detailed description of each position on the scale.

[edit] Measurement of light pollution and global effects

False colors show various intensities of artificial light — both direct and indirect — that reach space (Image credit: P. Cinzano)

Measuring the effect of sky glow on a global scale is a complex procedure. The natural atmosphere is not completely dark, even in the absence of terrestrial sources of light. This is caused by two main sources: airglow and scattered light.

At high altitudes, primarily above the mesosphere, UV radiation from the sun is so intense that ionization occurs. When these ions collide with electrically neutral particles they recombine and emit photons in the process, causing airglow. The degree of ionization is sufficiently large to allow a constant emission of radiation even during the night when the upper atmosphere is in the earth's shadow.

Apart from emitting light, the sky also scatters incoming light, primarily from distant stars and the milky way, but also sunlight that is reflected and backscattered from interplanetary dust particles (the so-called Zodiacal light).

The amount of airglow and zodiacal light is quite variable but given the most optimal conditions the darkest possible sky has a brightness of about 22 magnitude/square arcsecond. If a full moon is present, the sky brightness increases to 18 magnitude/sq. arcsecond, 40 times brighter than the darkest sky. In densely populated areas a sky brightness of 17 magnitude/sq. arcsecond is not uncommon, or as much as 100 times brighter than is natural.

To precisely measure how bright the sky gets night time satellite imagery of the earth is used as raw input for the number and intensity of light sources. These are put into a physical model^[6] of scattering due to air molecules and aerosoles to calculate cumulative sky brightness. Maps that show the enhanced sky brightness have been prepared for the entire world[5].

Inspection of the area surrounding Madrid reveals that the effects of light pollution caused by a single large conglomeration can be felt up to 100 km away from the center. Global effects of light pollution are also made obvious. The entire area comprising of southern England, Netherlands, Belgium, west Germany, and northern France have a sky brightness of at least 2 to 4 times above normal. The only place on continental Europe where the sky can attain its natural darkness is in northern Scandinavia.

In North America the situation is comparable. From the east coast to west Texas up to the Canadian border there is very significant global light pollution.

[edit] Consequences of light pollution

Light pollution wastes energy, obscures the night sky, harms human health, disrupts ecosystems and can reduce security.

[edit] Energy waste

Lighting consumes one fourth of all energy consumed worldwide, and case studies have shown that commonly 50 to 90 percent of building lighting is unnecessary for the purposes required. Energy is wasted when light does not fall on its intended target, as when lighting fixtures allow light to go up instead of (as is generally preferred) downward. Waste also occurs when more light is generated than needed. Many governments are looking for ways to reduce energy use after signing the Kyoto Protocol, and individuals, organizations and local authorities are increasingly improving lighting efficiency in order to reduce energy consumption.

This composite satellite photograph of the earth at night is one example of energy waste, as the visible upward-directed light does not usually provide useful or intended illumination. (Photo credit: NASA)

[edit] Interference with astronomical observations

Most urban dwellers cannot see a host of objects in the night sky, with the exception of the moon and bright planets.^[7][8] This "whiteout" zone can stretch many tens of kilometers. This hurts amateur astronomers, and it has been suggested that it also diminishes public understanding of space, astronomy, and science in general. ([6]; ^[9]) . Light pollution has also forced some professional astronomical observatories to move, such as the Royal Observatory, Greenwich, and prevents deep observations at other locations (e.g. Mount Wilson Observatory).

[edit] Effects on human health and psychology

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^[10] use human health as an explicit criterion for proper interior lighting. Health effects of over-illumination or improper spectral composition of light are as follows: increased headache incidence, worker fatigue, medically defined stress, decrease in sexual function and increase in anxiety^{[11][12][13][14]}.

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. 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.^[15][16]

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. ^[17][18]

[edit] Disruption of ecosystems

Life evolved with natural patterns of light and dark, so disruption of those patterns influences many aspects of animal behavior.^[19] Light pollution can confuse animal navigation, alter competitive interactions, change predator-prey relations, and influence animal physiology.

Studies suggest that light pollution around lakes prevents zooplankton, such as Daphnia, from eating surface algae, helping cause algal blooms that can kill off the lakes' plants and lower water quality. ^[20] Light pollution may also affect ecosystems in other ways. For example, Lepidopterists and entomologists have documented that night-time light may interfere with the ability of moths and other nocturnal insects to navigate.^[21] Night blooming flowers that depend on moths for pollination may be affected by night lighting, as there is no replacement pollinator that would not be affected by the artificial light. This can lead to species decline of plants that are unable to reproduce, and change an area's longterm ecology.

Migrating birds can be disoriented by lights on tall structures. Estimates by the U.S. Fish and Wildlife Service of the number of birds killed after being attracted to tall towers range from 4-5 million per year to an order of magnitude higher.^[22] The Fatal Light Awareness Program (FLAP) works with building owners in Toronto, Canada and other cities to reduce mortality of birds by turning out lights during migration periods.

Other well-known casualties of light pollution are sea turtle hatchlings emerging from nests on beaches. It is a common misconception that hatchling sea turtles are attracted to the moon. They are not; rather, they find the ocean by moving away from the dark silhouette of dunes and their vegetation, a behavior with which artificial lights interfere.^[23] Juvenile seabirds may also be disoriented by lights as they leave their nests and fly out to sea.

Nocturnal frogs and salamanders are also affected by light pollution. Since they are nocturnal, they wake up when there is no light. Light pollution may cause salamanders to emerge from concealment later, giving them less time to mate and reproduce.

A book that collects together research on the subject was recently released.^[24]

[edit] Loss of safety

It is generally agreed that many people require light to feel safe at night, but campaigners for the reduction of light pollution often claim that badly or inappropriately installed lighting can lead to a reduction in safety if measured objectively, and that at the very least, it is wrong to assume that simply increasing light at night will lead to improved safety.

The International Dark-Sky Association claims there are no good scientific studies that convincingly show a relationship between lighting and crime. Furthermore, the association claims that badly installed artificial lights can create a deeper contrast of shadows in which criminals might hide ^[25]. The New England Light Pollution Advisory Group claims that some light emitted by some fixtures can be a significant hazard to motorists, pedestrians, and bicyclists due to their scattering of light and glare [7].

The specific effects of outdoor lighting on safety are still a topic of debate, and formal research in the area is not well established.

[edit] Reducing light pollution

Reducing light pollution implies many things, such as reducing sky glow, reducing glare, reducing light trespass, and reducing clutter. The method for best reducing light pollution, therefore, depends on exactly what the problem is in any given instance. Possible solutions include:

• Utilizing light sources of minimum intensity necessary to accomplish the light's purpose.
• Turning lights off by timer or manually when not needed.
• Improving lighting fixtures, so that they direct their light more accurately towards where it is needed, and with less side effects.
• Adjusting the type of lights used, so that the light waves emitted are those that are less likely to cause severe light pollution problems.
• Evaluating existing lighting plans, and re-designing some or all of the plans depending on whether existing light is actually needed.

[edit] Improving lighting fixtures

A flat-lens cobra luminaire, which is a full-cutoff fixture, is preferable for reducing light pollution. It ensures that light is only directed below the horizontal, which means less light is wasted through directing it outwards and upwards.

This drop-lens cobra luminaire allows light to escape sideways and upwards, where it may cause problems.

The use of full cutoff lighting fixtures, as much as possible, is advocated by most campaigners for the reduction of light pollution. It is also commonly recommended that lights be spaced appropriately for maximum efficiency, and that lamps within the fixtures not be overpowered.

A full cutoff fixture, when correctly installed, reduces the chance for light to escape above the plane of the horizontal. Light released above the horizontal may sometimes be lighting an intended target, but often serves no purpose. When it enters into the atmosphere, light contributes to sky glow. Some governments and organizations are now considering, or have already implemented, full cutoff fixtures in street lamps and stadium lighting.

The use of full cutoff fixtures may help to reduce sky glow by preventing light from escaping unnecessarily. Full cutoff fixtures usually prevent luminaries from being directly visible, so the effects of glare may also be reduced by the nature of their design. Campaigners also commonly argue that full cutoff fixtures are more efficient than other fixtures, since light that would otherwise have escaped into the atmosphere is instead directed towards the ground.

The use of full cutoff fixtures may allow for lower powered bulbs to be used in the fixture with the same, or sometimes better effect due to being more carefully controlled. In every lighting system, some sky glow also results from light reflected from the ground. This reflection can be reduced, however, by being careful to avoid overpowering the lamp within the fixtures, and setting spacing between lights appropriately.^[26]

A common criticism of full cutoff lighting fixtures is that they are sometimes not as aesthetically pleasing to look at. This is most likely because historically there has not been a large market specifically for full cutoff fixtures. Due to the specificity with their direction of light, full cutoff fixtures sometimes also require expertise to install for maximum effect.

Another criticism of full cutoff lighting, particularly in the USA, is that luminaires with full cutoff distributions typically have to be closer together than other light distributions used to meet the same roadway lighting requirements specified by the Illuminating Engineering Society of North America, of light level, uniformity and glare (Keith, Journal of the Illuminating Engineering Society, 2000, 2002 and 2003). This means that using full cutoff luminaires corresponds to increased initial costs, maintenance costs, operating costs, energy use, energy pollution, and possibly light pollution, compared to using other distributions to meet the same roadway lighting requirements.

[edit] Adjusting types of light sources

Several different types of light sources exist, each having different properties that determine their appropriateness for certain tasks, particularly efficiency and spectral power distribution. It is often the case that inappropriate light sources have been selected for a task, either due to ignorance or because more sophisticated light sources were unavailable at the time of installation. Therefore, badly chosen light sources often contribute to light pollution unnecessarily. By re-assessing and changing the light sources used, it is often possible to reduce pollutive effects.

Some types of light sources, in order of energy efficiency, are:

Many astronomers prefer their neighboring societies to use low pressure sodium lights as much as possible, because the single wavelength involved is comparably easy to filter. The low cost of operating sodium lights is another feature. In 1980, for example, San Jose, California, replaced all street lamps with low pressure sodium lamps, whose light is easier for nearby Lick Observatory to filter out. Similar programs are now in place in Arizona and Hawaii.

Disadvantages of low pressure sodium lighting are that fixtures must usually be larger than competing fixtures, color cannot be distinguished — due to its emitting only a single wavelength of light (see security lighting) — and conflicts with yellow traffic lights are observed. Due to the substantial size of the light emitting part of the lamp, the arc tube, control of light emissions from low pressure sodium luminaires is very difficult resulting in higher amounts of light pollution from luminaires running these lamps than any other light source except fluorescent tubes. This has led many authorities to instead adopt more controllable high pressure sodium lighting for their street lights.

Because of the effects of atmospheric scatter, particularly Rayleigh scatter, different sources produce dramatically different amounts of skyglow from the same amount light sent into the atmosphere. This is a basic result of the fact that the sky is blue, and so reflects violet and blue light (shortest wave radiation) much more than any others (longer wave radiation.) A simple metric for this phenomenon is the Rayleigh Scatter Index, discussed in [[8]] a presentation to the 2003 IDA Conference which indicates that high pressure sodium produces roughly one-third to one-half of the skyglow that metal halide does, based on the same amount of light entering the atmosphere.

[edit] Re-designing lighting plans

In some cases, evaluation of existing plans has determined that more efficient lighting plans are possible. For instance, 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.^[27] 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.

In another example, the city of Calgary has recently replaced most residential street lights with models that are comparably energy efficient [9]. The motivation is primarily operation cost and environmental conservation. The costs of installation are expected to be regained through energy savings within six to seven years.

[edit] Organizations

As well as a variety of local groups, several large organizations have evolved, with the primary goal of informing and campaigning about light pollution.

• The International Dark-Sky Association (IDA) campaigns for reduced light pollution, mostly in the USA but with a world-wide reach.
• The Campaign for Dark Skies (CfDS) is part of the British Astronomical Association, and campaigns for reduced light pollution in the United Kingdom.
• IDA-UAI-CieloBuio, Italian joint organization by local IDA representative, Unione Astrofili Italiani, CieloBuio volunteer people.

[edit] See also

• History of street lighting in the United States
• Lighting
• List of environmental health hazards
• National Dark Sky Week
• 'Scuse Me While I Miss the Sky, an episode of the television series The Simpsons dedicated to light pollution.

[edit] References

[edit] External links

Wikimedia Commons has media related to:

Light pollution

[edit] Campaign groups

• International Dark-Sky Association
  • Links and Web Resources
  • Austria: Verein Kuffner Sternwarte (How many stars?)
• Campaign for Dark Skies (UK)
• New England Light Pollution Advisory Group
• SELENE (New York)
• Citizens for Responsible Lighting (based around a distributed discussion group)
• Virginia Outdoor Lighting Taskforce
• Italian site of IDA-UAI-CieloBuio
• Fatal Light Awareness Program (FLAP) (Toronto)

[edit] Research about light pollution

• The Discover article relating light pollution to insects, birds, and breast cancer (requires paid registration)
• Ecology of the night symposium (2003 conference)
• "Ecological Consequences of Artificial Night Lighting" (2002 conference, by the Urban Wildlands Group)
• Light pollution and the protection of the night environment, UNESCO, IDA Regional Meeting, 360 pages,(2002) English — Italian. Proceedings are available as a downloadable PDF.

[edit] Collections of links related to light pollution

• Open Directory Project: Light Pollution

[edit] Miscellaneous

• Utah Skies Light Pollution Information (light pollution information and solutions too!)
• The night sky in the World (satellite monitoring of artificial light)
• Light Pollution Awareness Site (USA)
• Santa Clara Valley Lighting & Lick Observatory (information)
• Alliance for Lighting Information — a resource for information on lighting with emphasis on the interaction between exterior lighting and humans.
• http://groups.yahoo.com/group/OutdoorLighting-Forum/ An online forum for discussing light pollution.
• DarkSky List Forum (email discussion group and resource library)
• Reduction in light pollution achieved near the observatories in Chile
• Possible light pollution in Death Valley National Park as Las Vegas grows
• Is Light Pollution Killing Our Birds? - because it kills insects.
• Light Pollution in Adelaide South Australia — examples of good and bad lighting.
• Astronomical Society of South Australia light pollution page.