Helena Joyce
Light pollution is a growing global problem, with the highest increases in North America. It occurs when artificial light is allowed to shine outward and upward into the sky, instead of being directed downwards. Light pollution is largely the result of poor lighting design, with common sources including street lamps, exterior lights, and illuminated signs. Cities are the worst offenders, with the brightness of their skies enhanced by clouds, haze, dust, and air pollutants. The light pollution of cities can be seen from over 200 miles away, and the brightness of the night sky is increasing by around 10% each year.
| Characteristics | Values |
|---|---|
| Areas with the most light pollution | Miami, USA (2.6 times brighter than the global urban average); Denver-Aurora, USA (2.7 times brighter than the global urban average); Pittsburgh; Raleigh; New York; Tokyo |
| Cause of light pollution | Excess or inappropriate artificial light outdoors; light pollution occurs in three ways: glare, light trespass, and skyglow |
| Sources of light pollution | Street lamps, parking lot/shopping mall lights, exterior lights found on most homes/businesses, neon signs, illuminated signboards, unshielded pathway lights, streetlights |
| Effects of light pollution | Wastes energy, impacts human health and wildlife, increases climate emissions, disrupts ecosystems, impacts human circadian rhythms |
| Solution to light pollution | Turn off lights; use shielded, light-efficient fixtures; reduce the number of external lights; use motion-sensitive lights |
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Urban areas
In urban centres, light pollution is caused by a multitude of sources. Firstly, street lighting is a major contributor. Traditional streetlights, often using high-pressure sodium or metal halide lamps, emit a strong orange or white light that illuminates streets and public spaces. These lights are often left on throughout the night, creating a constant source of artificial light. Additionally, cities are characterised by a dense concentration of buildings, each requiring illumination. Office blocks, apartments, and commercial spaces utilise a range of lighting fixtures, from fluorescent tubes to LED spotlights, which collectively contribute to the overall brightness of the cityscape.
Another significant factor is the use of decorative and advertising lighting. Cities often employ decorative lighting displays to enhance the aesthetic appeal of landmarks, bridges, and historical monuments. While these displays may be visually captivating, they contribute to the overall light pollution levels. Similarly, advertising billboards, particularly digital ones, emit bright light to ensure visibility and attract attention. The intense brightness and changing nature of these displays can be disruptive to the natural darkness.
Furthermore, urban areas often experience the phenomenon of "light trespass". This occurs when light from one source spills over into areas where it is not intended or wanted. For example, light from a brightly lit stadium or shopping complex can intrude into neighbouring residential areas, disrupting the natural darkness that residents may desire or expect. Light trespass can also occur vertically, with light from streetlights or tall buildings reflecting off clouds or atmospheric particles, creating a diffuse glow that illuminates the night sky.
The impact of light pollution in urban areas extends beyond the mere obscuration of the night sky. It has significant ecological consequences, disrupting the behaviour and habitats of various species, including birds, insects, and nocturnal wildlife. Additionally, the excessive use of artificial lighting contributes to energy waste and increases carbon emissions, exacerbating climate change. The health and well-being of human residents are also affected, with potential links to sleep disorders, hormonal imbalances, and psychological issues.
To mitigate light pollution in urban areas, several strategies can be employed. Firstly, responsible lighting design is crucial. This includes using shielded or full-cut-off fixtures that direct light downwards, reducing light trespass. Energy-efficient LED lights with motion sensors or dimming capabilities can also help reduce light output when full illumination is unnecessary. Additionally, implementing lighting ordinances and regulations that limit the brightness, duration, and placement of lighting installations can effectively minimise light pollution levels. By combining efficient lighting technologies with thoughtful design and regulatory measures, urban areas can significantly reduce their impact on the natural night environment.
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Oil and gas fields
The rapid growth of the oil industry in North Dakota has resulted in a 500% increase in man-made light visible in the north unit of Theodore Roosevelt National Park between 2010 and 2013, according to the National Park Service's Natural Sounds and Night Skies Division. This light pollution has not only impacted the park but also the surrounding areas, including Little Missouri State Park in western North Dakota, where flares and electric lights from oil wells are visible on the horizon.
Oil and gas development projects, often located far from populated areas, can produce light pollution on a large scale. The infrastructure built around these sites, including equipment yards, drilling rigs, gas stations, and housing, contributes to the bright lighting needed for navigation and operations. Additionally, when oil comes to the surface, it often brings natural gas with it. In some cases, it may not be economically feasible to build pipelines to transport the gas, so it is burned off instead, creating a "billion-dollar bonfire."
The light pollution from oil and gas fields can have significant ecological impacts, particularly for birds. The bright lights can disorient them, throwing them off their migration paths, and the loss of a dark night sky can have deadly consequences. Efforts are being made to address this issue, such as the work of Bill Wren at the University of Texas McDonald Observatory, who aims to change the way the oil and gas industry lights their nighttime activities to reduce light pollution.
While oil and gas fields can contribute to light pollution, it is important to note that the lighting is necessary for the safety of workers and the security of the sites. However, there may be opportunities to improve lighting techniques and technologies to reduce light pollution and minimize negative ecological impacts while still ensuring the safety and functionality of these industrial sites.
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Poor lighting design
One example of poor lighting design is the use of luminaires with full cutoff distributions. According to design investigations, these luminaires need to be placed closer together to meet the same light level and uniformity requirements as other types of luminaires. This can result in over-illumination or poor uniformity, which can be more detrimental than direct uplight created by fewer cutoff or semi-cutoff fixtures. Flat-lens cobra luminaires, which are full-cutoff fixtures, are effective in reducing light pollution by directing light only below the horizontal, reducing the amount of wasted light. However, drop-lens cobra luminaires allow light to escape sideways and upwards, contributing to light pollution.
Street lights, parking lot and shopping mall lights, exterior lights on homes and businesses, and neon signs are all common sources of light pollution due to poor lighting design. This type of lighting often produces glare, which is bright and uncomfortable light that interferes with vision and can even be dangerous, causing accidents on the road. Poor lighting design can also lead to light trespass, where artificial light unintentionally spills into other people's properties or spaces, causing conflict and disrupting natural cycles.
The adverse effects of light pollution on human health have been documented in medical research. Excessive light exposure can lead to increased headaches, worker fatigue, medically defined stress, decreased sexual function, increased anxiety, and potentially other mental and physical health issues. Light pollution also disrupts circadian rhythms, the natural 24-hour cycles that are essential for human and animal welfare.
To combat light pollution caused by poor lighting design, it is recommended to use shielded lights that reduce glare, dim lights to provide the appropriate amount of illumination, and turn off unnecessary lights to conserve energy and reduce light spill. IDA-certified Dark Sky Lighting is designed to minimize glare, light spill, and skyglow, and is available in a variety of fixtures. Proper lighting design and technology can help reduce light pollution and its negative impacts on the environment and human health.
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Clouds
Light pollution is a pressing issue, particularly in industrialized, densely populated areas of North America, Europe, and Asia, as well as major cities in the Middle East and North Africa. It is caused by artificial light from cars, streetlamps, offices, factories, advertising, and buildings, which turns night into day. This phenomenon is known as "sky glow," and it has severe ecological effects, influencing human and animal circadian rhythms and disrupting ecosystems.
While light pollution is predominantly associated with urban environments, it can also impact remote areas. Clouds play a significant role in amplifying light pollution, particularly in cities. Clouds over cities enhance sky brightness by reflecting light downward and increasing scattering. This effect intensifies the brightness of the night sky, making it challenging for people in these areas to observe celestial objects.
The presence of clouds can dramatically amplify the luminance of the sky. For instance, in Berlin, cloud coverage increased sky luminance by a factor of 10.1 in one location and by a factor of 2.8 at 32 km from the city center. Additionally, overcast nights in the city were found to be 4.1 times brighter than clear rural moonlit nights. This amplification effect has significant implications for chronobiological and chronoecological studies in urban areas.
The impact of clouds on light pollution is influenced by factors such as the level of cloudiness, the genus of clouds, and the altitude of their base. Among the various types of clouds, Altocumulus, Cirrocumulus, and Cumulonimbus are particularly associated with higher light pollution. The brightness of the night sky is most influenced by the scattering of light on low-altitude clouds, while high-level clouds contribute the least.
Furthermore, clouds can act as thick collections of aerosols, which are small water droplets that are highly reflective. These aerosols increase the scattering of light, further enhancing the brightness of the night sky. In certain conditions, such as freezing temperatures, a layer of aerosols can form below specific cloud types, contributing to the overall effect on light pollution.
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Human health and wildlife
Light pollution is a human-made alteration of outdoor light levels from those occurring naturally. It occurs most in highly populated places, such as the 600 urban areas with populations of 500,000 or more. Some of the worst-affected cities include Miami and Denver-Aurora, which are 2.6 and 2.7 times brighter than the global urban average, respectively. Other factors that influence light pollution levels include geographical and cultural factors, such as cities in northern latitudes experiencing less sunlight or arid countries with more evening activity.
Human Health
Research suggests that artificial light at night can negatively impact human health. Studies have linked light pollution to various health risks, including obesity, depression, sleep disorders, diabetes, and even certain types of cancer.
For example, a study in Israel found a correlation between outdoor artificial light at night and breast cancer. Women living in brightly lit areas had a 73% higher risk of developing breast cancer than those in areas with less artificial lighting.
Artificial light at night can also disrupt the production of hormones and disturb our natural sleep patterns, leading to issues like dissatisfaction with sleep quality, excessive sleepiness, and impaired daytime functioning.
Wildlife
Light pollution has been known to affect wildlife for thousands of years, with hunters and fishers using torches and lamps to attract their prey. However, with the advent of electricity, the problem has become more pervasive and widespread.
Nocturnal animals are particularly affected by light pollution, as it alters their nighttime environment and ecology. Predators use light to hunt, while prey species use darkness as cover. Artificial lights can also impact the breeding and feeding habits of amphibians, such as frogs, and disrupt the nocturnal activity of wetland habitats.
Additionally, light pollution can attract or repel certain organisms, leading to habitat loss and changes in day/night patterns, which can further affect reproductive cycles and overall ecosystem dynamics.
Conservation and advocacy groups, such as DarkSky International, work to protect communities and wildlife from light pollution by establishing codes and statutes to reduce its impact.
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Frequently asked questions
Light pollution occurs most in urban areas, with cities accounting for most light pollution. The highest increases in light pollution have been recorded in North America.
Some of the most light-polluted cities in the world include Miami, Denver-Aurora, and Pittsburgh.
Light pollution in cities is caused by the excessive use of artificial light outdoors, such as street lamps, exterior lights, and illuminated signs, which send light upward into the sky instead of downward.
