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.

Image:Empire State Building Night.jpg Light pollution is excess or obtrusive light created by humans. Among other effects, it causes adverse health effects, obscures most 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 industrialised, 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]; Federal Aviation Administration, 2005). Similar intentions are yet to be expressed by authorities in most other countries, however.

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Light pollution as a problem

"Light pollution" (also known as photopollution, luminous pollution) refers to light that people find annoying, wasteful or harmful. Some skeptics claim that light pollution has little residual effect, because it does not leave remnant damage to the environment as do air pollution, water pollution and soil contamination.

Campaigners wishing to reduce light pollution, however, reason that it is unrealistic to expect populations to ever switch off light en-masse, due to industrial society's economic reliance on artificial light. They posit, therefore, that it is a problem synonymous with traditional forms of pollution, where established trends in society have long term negative effects. These arguments mesh with energy conservation advocates who contend that light pollution must be addressed by changing the habits of society, so that lighting is used more efficiently, with less wastage 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 recognise 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[2].

Since not everyone is irritated by the same lighting sources, use of the term "Light Pollution" has a measure of subjectivity. It is common for one person's light "pollution" to be light that is desirable for another. One example of such a case is with advertising material, such as when an advertiser wishes for particular lights to be brightly 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 neighbour is generally wasted and pollutive light. Disputes are still common, however, when deciding action.

Light levels can be quantified by field measurement or mathematical modeling, with results typically displayed as an isophote map or light contour map. Differences in opinion over what light is considered reasonable, and who should be responsible, means that negotiation must sometimes take place between parties. 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.

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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, overillumination, glare, clutter, and sky glow. It is common, however, for annoying or wasteful light to fit several of these categories.

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Light trespass

Light trespass occurs when unwanted light enters one's property, for instance, by shining over a neighbour'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 trespass 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 severely-restricted light emissions. A large number of cities in the U.S. have developed stringent standards for outdoor lighting to protect such observatories.

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Over-illumination

Over-illumination is the excess use of light. Specifically within the United States, over-illumination is responsible for approximately two million barrels of oil per day in energy wastage. This is based upon U.S. consumption of equivalent of 50 million barrels per day of petroleum [3], 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 lihgting[4].) 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<ref>Lumina Technologies, Santa Rosa, Ca., Survey of 156 California commercial buildings energy use, August, 1996</ref> of energy consumed in lighting is unneeded or gratuitous.

An alternative calculation starts with the fact that commercial building lighting consumes in excess of 716 trillion kilowatt hours (1999 data) of electricity per annum[5], 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 globes, 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.

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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 seeing 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 categorised into different types. One such classification has been developed by Bob Mizon, coordinator for the British Astronomical Association's Campaign for Dark Skies:

  • 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.
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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 organisation who installed the lights, their placement and design may even be intended to distract drivers, and can contribute to accidents.

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Sky glow

Image:Lightmatter la at night 001.jpg 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 have begun to use the Bortle Dark-Sky Scale, to quantify sky glow, since it was published in Sky & Telescope magazine (Bortle, 2001). 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..

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Consequences of light pollution

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

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Energy waste

Image:Earth at Night.jpg 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, organisations and local authorities are increasingly improving lighting efficiency in order to reduce energy consumption.

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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. ("The Problem with Light Pollution", 1996; "Estimating the Level of Sky Glow Due to Cities", 1996). 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]; the British House of Commons, "First Special Report ...", 2003) . 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).

(Natural Bridges National Monument, Utah has the least light pollution and the darkest skies in the continental United States, according to a recent study by Backpacker magazine ("America's Last Wild Places", 2004)).

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Effects on human health and psychology

In particular common levels of office fluorescent lighting in offices is 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. There is clear evidence that levels of light in most office environments in the U.S. lead to increased stress as well as increased worker errors (DiLouie, 2006) (Bain, 1997).

Medical research on the effects of excessive light on the human body is extensive and there is clear evidence that many different adverse health effects are caused by light pollution or excessive light exposure:

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Disruption of ecosystems

Life evolved with natural patterns of light and dark, so disruption of those patterns influences many aspects of animal behavior (Longcore and Rich 2004). 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 (Moore et al., 2000). 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 (Frank 1988). 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 (Malakoff 2001). The Fatal Light Awareness Program 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 (Salmon 2003). 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.

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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, and that at the very least, it is wrong to assume that simply increasing light at night will lead to improved safety.

For example, 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 [7]. 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 [8].

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

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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.
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Improving lighting fixtures

Image:Flat-lens cobra luminaire.jpg

Image:Drop-lens cobra luminaire.jpg

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 organisations 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 ([NYSERDA-Planners], 2002).

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.

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Adjusting types of light sources

Several different types of light sources exist, each consisting of different properties that determine their appropriateness for certain tasks, as well as their efficiency. 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:

Type of light source Colour Efficacy
(lumens per watt)
Low pressure sodium yellow 80 - 200
High pressure sodium yellowish-pink 90 - 130
Metal Halide bluish-white/white 60 -120
Mercury Vapour blue-greenish white 13 - 48
Incandescent yellow/white 8 - 25

Many astronomers prefer their neighbouring 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, colour cannot be distinguished, due to its emitting only a single wavelength of light (see security lighting), and conflicts with yellow traffic lights. 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.

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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 commissioned by the Office of the Deputy Prime Minister in the United Kingdom ("Towards better practice", 2005). 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.

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Organisations

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

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See also

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References

  • "Light Pollution: Responses and Remedies" By Bob Mizon. ISBN 1-85233-497-5 (Springer, 2001)
  • "America's Last | first=John E. | title=Observer's Log - Introducing the Bortle Dark-Sky Scale | date
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External links

Template:Commons

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Campaign groups

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Research about light pollution

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Collections of links related to light pollution

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Miscellaneous

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