Light pollution refers to artificial lighting that alters the natural patterns of light and dark in ecosystems. In a descriptive sense, light pollution occurs when artificial light is used in a poor or excessive way, especially at night, causing negative effects in the view of the night sky. Light pollution has negative effects, including affects public safety, human health, obscuring the night sky, disrupting ecosystems and nature, overuse of energy, etc. Light pollution makes it harder for people in cities that use excessive artificial light, and like other pollutants it can harm our nature. Light pollution is not only a phenomenon resulting from a specific source or kind of pollution, it is also a contributor to the collective impact of various sources of pollution. Light pollution is caused by inefficient or unnecessary use of artificial light. Specific categories of light pollution include light trespass, over-illumination, glare, light clutter, and skyglow. For example, advertising and signs, excessive holiday decorations, inappropriate building exterior and interior lighting, misdirected streetlights, illuminated sporting venues, parking lots and commercial properties, etc. An offending light source often falls into more than one of these categories.
Although this type of pollution can exist throughout the day, its effects are magnified during the night. It has been estimated that more than 4/5 of the world's people, including more than 96% of Europeans and Americans live under light-polluted skies. More than 20% of the world's land area is affected by skyglow. The area affected by artificial illumination continues to increase. A major side effect of urbanization, light pollution is blamed for compromising health, disrupting ecosystems, and spoiling aesthetics. Studies show that urban areas are more at risk. Globally, it has increased every year.
Solutions to light pollution are often steps like adjusting light fixtures or using more appropriate light bulbs. Further remediation can be done with more efforts to educate the public in order to push legislative change. However, because it is a man-made phenomenon, addressing its impacts on humans and nature has political, social, and economic considerations.
Light Trespass
Light trespass occurs when unwanted light enters one's property. A common light trespass problem occurs when a strong light enters the window of one's home from the outside, causing problems such as sleep deprivation. A number of cities in the US have developed standards for outdoor lighting to protect the rights of their citizens against light trespass.
Over-Illumination
An office building is illuminated by high-pressure sodium lamps shining upward. Much light goes into the sky and neighboring apartment blocks, causing light pollution. Over-illumination is the excessive and unnecessary use of light. A large and overabundant amount of electricity is required to support light consumption in the United States. American cities emit three to five times more light to space per capita compared to German cities.
Light Clutter
Light clutter refers to excessive groupings of lights. Some strips display excessive groupings of ads lights. This is a classic example of light clutter. Groupings of lights might 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 advertisements surround the roadways. Depending on the motives of the person or organization that set up the lights, their placement and design can even be intended to distract drivers, and can contribute to accidents.
Glare
Glare can be categorized into different types. Disability glare describes effects such as being blinded by oncoming car lights, or light scattering in fog or in the eye, reducing contrast, as well as reflections from print and other dark areas that render them bright, with a significant reduction in sight capabilities. Discomfort glare does not typically cause a dangerous situation in itself, though it is annoying and irritating at best. It can potentially cause fatigue if experienced over extended periods. Glare light scattering in the eye causes loss of contrast and leads to unsafe driving conditions.
Sky Glow
Sky glow is the bright haze above cities that is produced from excessive artificial lighting at night. This type of light pollution is created from artificial light reflecting in the sky and bouncing around the different types of particles that reside in the atmosphere. The effect of sky glow can be harmful in astronomy and on the health of many organisms. It worsens the visibility of the stars, and significantly increases the natural light levels at night.
From Satellites
Also contributing to light pollution are artificial satellites. With increasing numbers of satellite constellations, members of the astronomical community, notably the IAU, fear that light pollution will increase significantly, one of many concerns reported in the media regarding satellite overcrowding. Public discourse surrounding the continuing deployment of satellite constellations includes multiple petitions by astronomers and citizen scientists.
Light pollution has detrimental impacts on animals, human health, and ecosystem functions and services. Only the damage to ecosystems is estimated as 3.36 trillion dollars per year.
Public Health Impact
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. Health effects of over-illumination or improper spectral composition of light may include increased headache incidence, worker fatigue, carcinogen, medically defined stress, and increase in anxiety. Likewise, animal models have been studied demonstrating unavoidable light to produce adverse effects on mood and anxiety. Light intrusion, even if dim, is likely to have measurable effects on sleep disruption and melatonin suppression. Continuous chronic circadian, sleep and hormonal disruption may have longer-term health risks. For those who need to be awake at night, light at night also has an acute effect on alertness and mood.
Effect on Astronomy
Astronomy is very sensitive to light pollution. The night sky viewed from a city bears no resemblance to what can be seen from dark skies. Skyglow, the scattering of light in the atmosphere at night reduces the contrast between stars and galaxies and the sky itself, making it much harder to see fainter objects. Even at apparent clear night skies, there can be a lot of stray light that becomes visible at longer exposure times in astrophotography. By means of software, the stray light can be reduced. However, at the same time, object detail could be lost in the image.
Some astronomers use narrow-band nebula filters that allow only specific wavelengths of light commonly seen in nebulae, or broad-band "light pollution filters that are designed to reduce 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. Unfortunately, these light pollution reduction filters are not a cure for light pollution. The filters reduce the brightness of the object under study and this limits the use of higher magnifications. Light pollution reduction filters work by blocking light of certain wavelengths that alters the color of the object, often creating a pronounced green cast. Furthermore, light pollution reduction filters work only on certain object types, mainly emission nebulae. They are of little use on galaxies and stars. No filter can match the effectiveness of a dark sky for visual or photographic purposes.
Ecological Impact
While light at night can be beneficial, neutral, or damaging for individual species, its presence invariably disturbs ecosystems. Light pollution poses a serious threat in particular to nocturnal animals, having negative impacts on plant and animal physiology. It can confuse animal navigation, alter competitive interactions, change predator-prey relations, and cause physiological harm. The rhythm of life is orchestrated by the natural diurnal patterns of light and dark, so disruption to these patterns impacts the ecological dynamics.
Studies suggest that light pollution around lakes prevents zooplankton from eating surface algae, causing algal blooms that can kill off the lakes' plants and lower water quality. Light pollution may also affect ecosystems in other ways. Significant declines in some insect populations have been suggested as being at least partially mediated by artificial lights at night. For example, entomologists have documented that nighttime light may interfere with the ability of nocturnal insects to navigate. It can also have a negative impact on insect development and reproduction. Night-blooming flowers that depend on nocturnal insects for pollination might 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 long term ecology.
Lights on tall structures can disorient migrating birds. Estimates of the number of birds killed after being attracted to tall towers range from four to five million per year to an order of magnitude higher. The Fatal Light Awareness Program works with building owners to reduce mortality of birds by turning out lights during migration periods. Another study has found that the lights produced by the Post Tower have affected 25 bird species. As a result, they discovered that decreasing the use of excessive lights increased the survival rate of bird species. In some cities, the Lights Out program run in partnership with the city organizes volunteers during migration to document bird–building collisions, transport injured birds to rehabilitation, and use the resulting data to advocate for bird-friendly lighting treatments on buildings.
Increase in Atmospheric Pollution
A study presented at the American Geophysical Union meeting found that light pollution destroys nitrate radicals thus preventing the normal night time reduction of atmospheric smog produced by fumes emitted from cars and factories.
Reduction of Natural Sky Polarization
Light pollution is mostly unpolarized, and its addition to moonlight results in a decreased polarization signal.
In the night, the polarization of the moonlit sky is strongly reduced in the presence of urban light pollution, because scattered urban light is generally not strongly polarized, especially in urban areas. When the moon is not up, it is possible for the sky to become polarized to some degree, particularly in the case of strongly non-uniform light sources. The polarization pattern of the sky cannot be directly perceived by the human visual system. However, it is used by some animals for orientation and navigation.
Economic Relation
Researchers are looking at the impact of light pollution on this group of evening workers. Numerous studies that found increased risks of cancers in groups of evening workers. Further research should attempt to determine the safest amount of light exposure, in terms of duration and intensity that would be most desirable for both humans and animals. With the development of this data, possible safety limits could be applied for light levels. Ideally, the light level would maintain human benefits, while also decreasing or fully removing the negative impacts on animals.
Noctalgia
Noctalgia is the feeling of difficulty seeing a starry night sky. This also includes the feeling of sky grief, where people no longer have the ability to look at the stars, something that has been done for most of human existence. The phenomenon also includes the grief over not being able to have the sense of awe and wonder that humans often experience when stargazing. The night sky deserves a global protection scheme as an important part of the global heritage.
Remediation
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 creation of unwanted or unneeded illumination. For example, reduce the amount of ads on streets and highways, limit the dates of holidays’ decoration lights. 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 with information about light pollution, the problems it causes, and how to reduce its impact. Researchers suggested that energy efficiency might not be enough to reduce the light pollution because of the rebound effect.
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. The use of full cutoff lighting fixtures 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 the number of luminaires being used as well as the wattage of each luminaire match the needs of the particular application. Many astronomers request that nearby communities use low-pressure sodium lights as much as possible because the principal wavelength emitted is comparably easy to work around or in rare cases filter out.
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 lighting stadiums only when there are people inside. Timers are especially valuable for this purpose. One of the world's first coordinated legislative efforts to reduce the adverse effect of this pollution on the city began in Flagstaff, Arizona, in the US There, ordinance development has taken place, with the full support of the population, often with government support, with community advocates, and with the help of major local observatories, including the United States Naval Observatory Flagstaff Station. Each component helps to educate, protect and enforce the imperatives to intelligently reduce detrimental light pollution.
(I appreciate Wikipedia for introducing light pollution. Please let me know if it is against copyright.)
