Light pollution



Light pollution is excess or obtrusive light created by humans. Among other effects, it disrupts ecosystems, can cause adverse health effects, obscures the stars for city dwellers, interferes with astronomical observatories, and wastes energy. 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. 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, 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. Similar intentions are yet to be expressed by authorities in most other countries, however.

Light pollution as a problem
"Light pollution" (also known as photopollution, luminous pollution) refers to light that is considered annoying, wasteful or harmful. It also causes damage to the environment and health, as do other forms of pollution such as air pollution, noise 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 man-made 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 its members information about light pollution, the problems it causes, and how to reduce its impact.

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.

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

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 problematic 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 trespass. 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 which citizens may use to identify offending structures and provides a mechanism for processing consumer inquiries and complaints.

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, noting that 60% of U.S. supply is from nuclear power, 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.) 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 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, 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.

Glare
Glare is often 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 also result in reduced contrast, due to light scattering in the eye by excessive brightness, or to reflection of light from dark areas in the field of vision, with luminance similar to the background luminance. This kind of glare is a particular instance of disability glare, called veiling glare.

Glare can be categorized into different types. One such classification is described in a book by Bob Mizon, coordinator for the British Astronomical Association's Campaign for Dark Skies. According to this classification:
 * Blinding Glare describes effects such as that caused by staring into the Sun. It is completely blinding and leaves temporary or permanent vision deficiencies.
 * Disability Glare describes effects such as being blinded by an oncoming cars lights, or light scattering in fog or in the eye reduces contrast, as well as reflections from print and other dark areas that render them bright, 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.

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-relevant lighting. For instance runway lighting may be confused with an array of suburban commercial lighting and aircraft collision avoidance lights may be confused with ground lights.

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 have begun to use the Bortle Dark-Sky Scale, to quantify sky glow, since it was published in Sky & Telescope magazine. 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.

Measurement of light pollution and global effects
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 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 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.

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 consisting of southern England, Netherlands, Belgium, west Germany, and northern France have a sky brightness of at least 2 to 4 times above normal (see above right). The only place in 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.

Energy waste
Lighting is responsible for one fourth of all energy consumed worldwide, and case studies have shown that several forms of over-illumination constitute energy wastage including non-beneficial upward direction of night-time lighting.

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 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. 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. However, such high interior lighting levels are not typical outside North America.

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.

Disruption of ecosystems
Life existed with natural patterns of light and dark, so disruption of those patterns influences many aspects of animal behavior. 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. 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. 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. 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. 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.

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. 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.

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

Effect on astronomy
Skyglow reduces the contrast between stars and galaxies in the sky and the sky itself, making it more difficult to detect fainter objects. This is one factor that has caused newer telescopes to be built in increasingly remote areas. Some astronomers use "nebula" filters, which are designed to reduce (but not eliminate) the effects of light pollution by filtering out spectral lines commonly emitted by sodium- and mercury-vapor lamps, thus enhancing contrast and improving the view of dim objects such as galaxies and nebulae.

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 using a timer or occupancy sensor 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.

Improving lighting fixtures




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 typically reduces the visibility of the lamp and reflector within a luminarie, so the effects of glare may also be reduced. Campaigners also commonly argue that full cutoff fixtures are more efficient than other fixtures, since light that would otherwise have escaped into the atmosphere may instead be directed towards the ground. However full cutoff fixtures may also trap more light in the fixture than other types of luminaires, corresponding to lower luminaire efficiency.

The use of full cutoff fixtures may allow for lower wattage lamps to be used in the fixtures, producing the same or sometimes a 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 use only the lowest wattage necessary for the lamp, and setting spacing between lights appropriately.

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, and because people typically like to see the source of illumination. 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, in terms of light level, uniformity and glare . The issue is very complex: the spread of light from any lamp depends largely on the design of the optics inside, and full-cut-off types are not *necessarily* closer together than the old stock that they replace - on the M5 motorway in SW England, for example, new FCOs were installed further apart than the old, deep-bowl types they replaced, on columns of similar height. Due to the complexity of roadway lighting design, sometimes existing lighting was not optimized at its design, so there is significant room for improvement. However, according to published research (see previous ref.s), when lighting designs are optimized, using full-cut-off luminaires does typically correspond 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.

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 scatter of light by the atmosphere, particularly Rayleigh scattering, different sources produce dramatically different amounts of skyglow from the same amount of 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 a brief article and a 2003 presentation to both the IDA Conference and the IESNA, which indicates that high pressure sodium produces roughly one-third to one-half of the skyglow that typical metal halide does, based on the same amount of light entering the atmosphere.

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. 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. 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.

The Swiss agency for energy efficiency (SAFE) uses a concept which promises to be of great use in the diagnosis and design of road lighting, i.e. "consommation électrique spécifique (CES)", which can be translated into English as "specific electric power consumption (SEC)". Thus, based on observed lighting levels in a wide range of Swiss towns, SAFE has defined target values for electric power consumption per metre for roads of various categories. Thus, SAFE currently recommends an SEC of 2 to 3 watts per meter for roads of less than 10 metre width (4 to 6 watts per metre for wider roads). Such a measure provides an easily applicable environmental protection constraint on conventional "norms", which usually are based on the recommendations of lighting manufacturing interests, who may not take into account environmental criteria. In view of ongoing progress in lighting technology, target SEC values will need to be periodically revised downwards.

Related Organizations

 * 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
 * Spanish Cel Fosc
 * Fatal Light Awareness Program (FLAP) (Toronto)
 * Starlight: a common heritage.
 * The Campaign for Dark Skies (CfDS) is part of the British Astronomical Association, and campaigns for reduced light pollution in the United Kingdom.

Research about light pollution

 * The Challenge article "Is Light Pollution Killing Our Birds"
 * 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.
 * Sherbrooke College Light pollution research activities
 * Adelaide's Light Pollution Examples of the good, bad and ugly lighting

Collections of links related to light pollution

 * Open Directory Project: Light Pollution
 * The Dark Side: an article in The New Yorker magazine about light pollution
 * Astronomical Society of South Australia article on Light Pollution

تلوث ضوئي Contaminació lumínica Světelné znečištění Lysforurening Lichtverschmutzung Contaminación lumínica Luma poluo Pollution lumineuse Contaminación lumínica Inquinamento luminoso זיהום אור Lichtvervuiling 光害 Zanieczyszczenie świetlne Poluição luminosa Light pollution Svetelné znečistenie Svetlobno onesnaženje Valosaaste Ljusförorening 光害