User:Jessicasabatini/Light pollution

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Light pollution is the presence of any unwanted, inappropriate, or excessive artificial lighting.[1][2] In a descriptive sense, the term light pollution refers to the many effects of any poorly implemented lighting sources, during the day or night. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind of pollution, but also as a contributor to the wider, collective impact of various sources of pollution.[3]

Although this type of pollution can exist throughout the day, its effects are magnified during the night with the contrast of the sky's darkness. It has been estimated that 83 percent of the world's people live under light-polluted skies and that 23 percent of the world's land area is affected by skyglow.[4][5][6] Studies show that urban areas are more at risk, but the area affected by artificial illumination continues to increase. As a major side-effect of urbanization, light pollution is blamed for compromising health, disrupting ecosystems, and spoiling aesthetic environments. Electricity is necessary in order to further support largely urbanized countries like, the United States. Globally, it has increased by at least 49% from 1992 to 2017.[7]

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. A single offending light source often falls into more than one of these categories.

Solutions to light pollution are often easy 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 the environment has political, social, and economic considerations.

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Light clutter
Light 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 advertisements surround the roadways. Depending on the motives of the person or organization that installed the lights, their placement and design can even be intended to distract drivers, and can contribute to accidents.

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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, the Milky Way, and significantly increases the natural light levels at night.

Issues to measuring light pollution
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 and illumination from the Moon. This is caused by two main sources: airglow and scattered light.

At high altitudes, primarily above the mesosphere, there is enough UV radiation from the sun at very short wavelengths to cause ionization. When the 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. Lower in the atmosphere all the solar photons with energies above the ionization potential of N2 and O2 have already been absorbed by the higher layers and thus no appreciable ionization occurs.

Apart from emitting light, the sky also scatters incoming light, primarily from distant stars and the Milky Way, but also the zodiacal light, sunlight that is reflected and backscattered from interplanetary dust particles.

The amount of airglow and zodiacal light is quite varied (depending, amongst other things on sunspot activity and the Solar cycle) but given optimal conditions, the darkest possible sky has a brightness of about 22 magnitude/square arc second. If a full moon is present, the sky brightness increases to about 18 magnitude/sq. arcsecond depending on local atmospheric transparency, 40 times brighter than the darkest sky. In densely populated areas a sky brightness of 17 magnitude/sq. an arcsecond is not uncommon, or as much as 100 times brighter than is natural.

Over-illumination
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. U.S homes consumed 81 billion kilowatthours (kWh) of electricity for lighting in 2020 according to the U.S. Energy Information Administration's (EIA). Additionally, the EIA reported that 208 billion kWh and 53 billion kWh of electricity were used for commercial and manufacturing buildings respectively in 2018.

Light use is not excessive in all developed countries. Amongst developed countries there are large variations in patterns of light use. American cities emit three to five times more light to space per capita compared to German cities.

Over-illumination stems from several factors:


 * Consensus-based standards or norms that are not based on vision science;
 * Improper design, by specifying higher levels of light than needed for a given visual 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;
 * "Daylight lighting" demanded by citizens to reduce crime or by shop owners to attract customers;
 * Substitution of old lamps with more efficient LEDs using the same electrical power; and
 * Indirect lighting techniques, such as illuminating a vertical wall to bounce light onto the ground.
 * Institutions who illuminate their buildings not to improve navigation, but "to show that its empire is inescapable".
 * Lighting is less for the benefit of seeing at night, and more for institutions to push working hours beyond natural daylight hours. A economic and financial gain as opposed to a necessity.

Most of these issues can be readily corrected with available, inexpensive technology, and with the resolution of 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.

In certain cases, an over-illumination lighting technique may be needed. For example, indirect lighting is often used to obtain a "softer" look, since hard direct lighting is generally found less desirable for certain surfaces, such as skin. The indirect lighting method is perceived as cozier and suits bars, restaurants, and living quarters. It is also possible to block the direct lighting effect by adding softening filters or other solutions, though intensity will be reduced.

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Economic impact
Research surrounding light pollution focuses on the quality of lighting and reducing our ability to clearly view the sky at night. However, light pollution has many root causes and effects across the spectrum of life. Since the time of the Industrial Revolution grew out of England and spread across the globe, major changes have been made in the way we live. Technological innovation is moving at a rapid pace. It is not uncommon to find 24-hour business, such as gas stations, convenience stores, and pharmacies. Hospitals and other healthcare facilities must be staffed 24 hours per day, seven days per week. With the rise of Amazon, many factories and shipping companies now operate 24x7 shifts to keep up with the demand of the new global consumer. These industries all require light, both inside and outside their facilities to ensure the safety of their workers as they move about their jobs and when the enter and depart the facilities. As a result, "40% of the United States and almost 20% of the European Union population has lost the ability to view the night sky…in other words, it is as if they never really experience nighttime."

With a focus on shift work and the continued need for 24-hour operations of specific sectors of the economy, researchers are looking at the impact of light pollution on this group of workers. In 2007 the International Agency for Research on Cancer (IARC) sought to bring notice to the risk from shift work as a probable risk for developing cancers. This move was the result of numerous studies that found increased risks of cancers in groups of shift workers. The 1998 Nurses Health Study found a link between breast cancer and nurses who had worked rotating night shifts in their young adult life. However, it is not possible to halt shift work in these industries. Hospitals must be staffed around the clock.

Research suggests that, like other environmental issues, light pollution is primarily a problem caused by industrialized nations. Numerous economic indicators have been examined to get a better sense of where light pollution was occurring around the globe. Countries with paved roads, an indicator of developed infrastructure, often had increased light pollution. Similarly, countries with a high rate of resource extraction also have high rates of light pollution. Also those with the highest GDP and high surface area described as urban and suburban also had the highest rates of light pollution.

China is an emerging leader in industrial and economic growth. A recent study of light pollution using the Defense Meteorological Satellite Program Operational Linescan System (DMSL/OLS) found that light pollution is increasing over the eastern coastal cities but decreasing over the industrial and mineral extraction cities. Specifically, urban areas around the Yangtze River delta, Pearl River delta, and Beijing-Tianjin area are specific light pollution areas of concern. Examining China as a whole, it was found that light pollution in the East and North was much higher than the West. This is consistent with major industrial factories located in the East and North while resource extraction dominates the West.

In 2009, following the United Nations declaration of The Year of Astronomy, researchers urged a better understanding of artificial light and the role it plays in social, economic, and environmental issues. Continued unfettered use of artificial light in urban and rural areas would cause a global shift with unpredictable outcomes. Focusing on the economic impact of increased energy consumption in light bulbs, or the move to energy efficiency of lighting, is not enough. Rather, the broader focus should be on the socio-economic, ecologic, and physiologic impacts of light pollution.

Humans require some artificial night light for shift work, manufacturing, street safety, and nighttime driving and research has shown that artificial light disrupts the lives of animals. However, recent studies suggest that we may be able to find a happy medium. A 2021 article examined seasonal light changes and its effect on all animals, but specifically mollusks. The article claims that previous light research primarily focuses on length of exposure to light. However, 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 on 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.

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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. This is one factor that has caused newer telescopes to be built in increasingly remote areas.

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, but at the same time, object detail could be lost in the image. The following picture of the area around the Pinwheel Galaxy (Messier 101) with the apparent magnitude of 7.5m with all stars down to an apparent magnitude of 10m was taken in Berlin in a direction close to the zenith with a fast lens (f-number 1.2) and an exposure time of five seconds at an exposure index of ISO 12800:

Some astronomers use narrow-band "nebula filters", which allow only specific wavelengths of light commonly seen in nebulae, or broad-band "light pollution 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. Unfortunately, these light pollution reduction (LPR) filters are not a cure for light pollution. LPR filters reduce the brightness of the object under study and this limits the use of higher magnifications. LPR filters work by blocking light of certain wavelengths, which alters the color of the object, often creating a pronounced green cast. Furthermore, LPR filters work only on certain object types (mainly emission nebulae) and are of little use on galaxies and stars. No filter can match the effectiveness of a dark sky for visual or photographic purposes.

Light pollution affects the visibility of diffuse sky objects like nebulae and galaxies more than stars, due to their low surface brightness. Most such objects are rendered invisible in heavily light-polluted skies above major cities. A simple method for estimating the darkness of a location is to look for the Milky Way, which from truly dark skies appears bright enough to cast a shadow.

In addition to skyglow, light trespass can impact observations when artificial light directly enters the tube of the telescope and is reflected from non-optical surfaces until it eventually reaches the eyepiece. This direct form of light pollution causes a glow across the field of view, which reduces contrast. Light trespass also makes it hard for a visual observer to become sufficiently adapted to the dark. The usual measures to reduce this glare, if reducing the light directly is not an option, include flocking the telescope tube and accessories to reduce reflection, and putting a light shield (also usable as a dew shield) on the telescope to reduce light entering from angles other than those near the target. Under these conditions, some astronomers prefer to observe under a black cloth to ensure maximum adaptation to the dark.

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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 waste and less creation of unwanted or unneeded illumination. 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. Research in 2017 suggested that energy efficiency may not be enough to reduce the light pollution because of the rebound effect.

Light levels can be quantified by field measurement or mathematical modeling, the results of which are typically rendered in isophote maps or light contour maps. To deal with light pollution, authorities have taken a variety of measures depending on the interests, beliefs, and understandings of the society involved. These measures range from doing nothing at all to implementing strict laws and regulations specifying how lights may be installed and used.

Reduction
"Improving lighting fixtures, so they direct their light more accurately towards where it is needed, and with fewer side effects.

Adjusting the type of lights used, so the light waves emitted are those that are less likely to cause severe light pollution problems. Mercury, metal halide and above all first generation of blue-light LED road luminaires are much more polluting than sodium lamps: Earth's atmosphere scatters and transmits blue light better than yellow or red light. It is a common experience observing "glare" and "fog" around and below LED road luminaires as soon as air humidity increases, while orange sodium lamp luminaires are less prone to showing this phenomenon.

Evaluating existing lighting plans, and re-designing some or all the plans depending on whether existing light is actually needed."

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Community awareness is also necessary in order to progress towards reducing light pollution. As, if more people are aware on the effects of artificial lighting, there could be effective legislative influence on mitigating it. Unfortunately, there are groups that may still not be completely knowledgeable on its various impacts. For example, cultural beliefs may be the reason some are holding back; around the world, darkness may be associated with evil whereas light would contrastingly be associated with progress in some cultures. Furthermore, societal standards have made humans more active during the day time, which may be another significant reason for the delay of increased knowledge and awareness. However, more recent studies show the public not only becoming more aware of the issue, but are also experiencing consequences of excessive artificial lighting. An assessment from 2020 shows an increase in citizen awareness in the late 20th century due to availability to internet search engines as well as the ability to engage globally. The assessment discussion further suggests that better information accessibility and voting may motivate more citizens to understand and thus care about the issue.