Helena Joyce
Light pollution, also known as photopollution or luminous pollution, is the presence of artificial light in otherwise dark conditions. Sources of light pollution include building exterior and interior lighting, advertising, outdoor area lighting, streetlights, and illuminated sporting venues. It is most severe in highly industrialized, densely populated areas and major cities in North America, Europe, Asia, the Middle East, and North Africa. The consequences of light pollution are vast, including adverse effects on human health, wildlife, and the environment. As light pollution continues to increase globally, it is important to evaluate and address this issue through responsible outdoor lighting practices. This involves implementing lighting designs and technologies that minimize light trespass, sky pollution, and energy consumption, while also considering the need for visibility and safety at night.
| Characteristics | Values |
|---|---|
| Definition | Light pollution is the presence of anthropogenic artificial light in otherwise dark conditions. |
| Sources | Building exterior and interior lighting, advertising, outdoor area lighting (e.g. car parks), offices, factories, streetlights, illuminated sporting venues. |
| Effects | Interferes with starlight, astronomical observatories, ecosystems, and human health. |
| Human Health Effects | Increased headaches, worker fatigue, medically defined stress, decreased sexual function, increased anxiety, disrupted sleep, impaired night vision, eyestrain, increased blood sugar levels, decreased leptin levels, risk of obesity, mental disorders, diabetes. |
| Environmental Effects | Alters life-sustaining behaviours in plants and animals, greater attraction for insects causing decreased populations, harms wildlife habitats, disrupts energy resources, disrupts circadian rhythms of organisms. |
| Severity | Most severe in highly industrialized, densely populated areas of North America, Europe, and Asia, and major cities in the Middle East and North Africa. |
| Solutions | Use compact fluorescent lamps (CFLs) and LED bulbs with warm white lighting, use shielded outdoor light fixtures, use timers and motion sensors, implement responsible outdoor lighting practices and standards. |
| Assessment Methods | Bortle Scale, Outdoor Site-Lighting Performance (OSP), remote sensing by satellites, theoretical models. |
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What You'll Learn
The Bortle Scale and other tools used to measure sky brightness
Light pollution is the presence of artificial light in otherwise dark conditions, and it is a growing global phenomenon. It competes with starlight in the night sky, interferes with astronomical observatories, and disrupts ecosystems and human health. Light pollution is most severe in highly industrialised, densely populated areas of North America, Europe, Asia, and major cities in the Middle East and North Africa.
To address light pollution, conservation methods have been established to protect certain landscapes based on the quality of their dark night skies. Examples include the International Dark Sky Places Program by the International Dark-Sky Association (IDA), the Royal Astronomical Society of Canada (RASC) Dark Sky Site Designations, and the Starlight Foundation certification program. These programs use various criteria, including objective measurements and subjective impressions, to assess and monitor light pollution levels.
One common tool used to measure sky brightness and light pollution is the Bortle Scale. Developed by John E. Bortle in 2001 and published in Sky & Telescope magazine, the Bortle Scale uses astronomical observations to quantify the amount of light pollution at a given location. It ranges from Class 1, representing the darkest skies where M33 (Triangulum Galaxy) can be observed with the naked eye, to Class 9, indicating the most extreme light pollution. Amateur astronomers and astrophotographers often refer to their sky quality reading using the Bortle Scale.
In addition to the Bortle Scale, other tools are available to measure sky brightness. These include sky quality meters, light pollution maps, and smartphone applications such as Clear Outside by FLO, which provides an accurate reading of a location's Bortle Scale class. Stellarium, a free planetarium software, also allows users to adjust light pollution settings to match their sky conditions. Furthermore, the Outdoor Site-Lighting Performance (OSP) method helps quantify and optimise lighting designs to minimise light trespass.
By utilising these tools and adopting responsible outdoor lighting practices, individuals and communities can take action to reduce light pollution and preserve the quality of the night sky.
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The impact of light pollution on human health
Light pollution is the presence of artificial light in otherwise dark conditions, and it is a growing global phenomenon. Sources of light pollution include building exterior and interior lighting, advertising, streetlights, and illuminated sporting venues. Light pollution has been increasing at twice the rate of population growth, with 83% of the global population living under light-polluted skies. This has led to the fading of our night sky, with fewer dark places to experience a sky full of stars.
Light pollution has been recognised as an environmental issue since the second half of the 19th century, but efforts to address it are relatively recent. The global dark-sky movement emerged in the 1980s, advocating for the protection of dark night skies and the reduction of light pollution.
Light pollution has been linked to a range of adverse health effects on humans. Medical research suggests that excessive light exposure or improper spectral composition of light may lead to increased headaches, worker fatigue, medically defined stress, decreased sexual function, and increased anxiety.
Preliminary studies have also found links between exposure to outdoor artificial light at night and risks for obesity, mental disorders, and diabetes. This is due to the impact of artificial light on the production of hormones, particularly melatonin, which is crucial for regulating sleep and circadian rhythms.
To reduce the impact of light pollution on human health, it is recommended to minimise exposure to artificial light, especially blue light. This can be achieved by using dimmers, lower-CCT light bulbs, and colour temperature apps that adapt electronic screen colours to the time of day. Shielding light fixtures and using lamps with a correlated colour temperature (CCT) of 3000 K or lower can also help mitigate the effects of light pollution.
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The ecological consequences of light pollution
Light pollution is a growing phenomenon that has harmful effects on wildlife and ecosystems. The proliferation of artificial light at night has become a global phenomenon, with 83% of people, including 99% of Europeans and Americans, living under light-polluted skies. Light pollution disrupts the natural cycles of light and the illumination of the environment, impacting the behaviour, biological rhythms, and physiological functions of living organisms.
At the individual level, light pollution can affect orientation and modify locomotor, eating, reproductive, and communication behaviours in plants and animals. It can also increase the attraction of insects, leading to a decline in insect populations, which negatively impacts all species that rely on insects for food or pollination. Some predators, such as fast-flying bats, can exploit this attraction to their advantage, affecting food webs and creating interspecific competition.
At the ecosystem level, light pollution can cause imbalances by modifying inter- and intra-species competitions, prey-predator balances, and the organisation of species communities. It creates a new ecological niche, attracting some nocturnal species while repelling others. For example, adult and hatchling sea turtles can become disoriented by lights, unable to find the ocean, while birds may collide with artificial structures due to disorientation. Migratory shorebirds may also face increased predation when lighting makes them more visible.
Light pollution also interferes with astronomical observatories and human health. It competes with starlight in the night sky, hindering astrophotography and the ability to observe the Milky Way galaxy. The excessive light exposure can lead to various adverse health effects, including headaches, worker fatigue, medically defined stress, decreased sexual function, increased anxiety, and sleep deprivation.
To address light pollution, organisations like DarkSky International and the Illuminating Engineering Society (IES) have developed principles for responsible outdoor lighting. These principles aim to prevent and reduce light pollution through the proper application of quality outdoor lighting. Additionally, communities have advocated for legislation and standards to protect citizens' rights against light trespass and minimise ecological and health impacts.
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The 5 Principles for Responsible Outdoor Lighting
Light pollution is a growing global issue, with 83% of the global population living under a light-polluted sky. The International Dark-Sky Association (IDA) and the Illuminating Engineering Society (IES) have jointly published the Five Principles for Responsible Outdoor Lighting to prevent and reduce light pollution through the proper application of quality outdoor electric lighting.
- Targeting: Light should only illuminate the objects, areas, or paths that need it. Lights should be shielded to prevent light trespass, which occurs when unwanted light enters someone else's property.
- Usefulness: Lights should be used only when needed and turned off when nobody is around to use them. For example, parking lots and sports facilities don't need to be lit after closing hours, and yard lights are unnecessary when no one is there.
- Control: Lights should be properly designed to avoid overlighting. The lowest effective light level should be selected, and glare should be minimised to prevent accidents for humans and wildlife.
- Timeliness: Lights should be turned on only when needed and turned off when they are not required. Timers can be used to automate this process.
- Energy Efficiency: Energy-efficient lighting technologies, such as LED lights, can be used to reduce energy consumption and lower costs.
By applying these principles, we can create a better quality of life for all living things, reduce light pollution, save energy and money, and minimise wildlife disruption.
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How to choose responsible outdoor lighting
Light pollution is a growing global issue, with 83% of the global population living under a light-polluted sky. It has been defined as the human-made alteration of outdoor light levels from those occurring naturally. Light pollution competes with starlight in the night sky, interferes with astronomical observatories, disrupts ecosystems, and has adverse health effects. It is most severe in highly industrialized, densely populated areas of North America, Europe, and Asia, and in major cities in the Middle East and North Africa.
To address this issue, organizations such as DarkSky International (IDA) and the Illuminating Engineering Society (IES) have developed principles for responsible outdoor lighting. Here are some guidelines on how to choose responsible outdoor lighting to reduce light pollution:
- Usefulness: Light should be produced only when needed. For example, consider using timers, motion sensors, or Smart Home installations to control lights automatically or remotely. Turn off unneeded outdoor lights, and light stadiums only when occupied.
- Targeted: Light should be directed only to the areas that require illumination. Use shields or curtains to prevent light from invading neighbouring properties or natural habitats.
- Appropriate: Light should be limited to the minimum brightness required. Test installations with different intensities and select the lowest light level that is functional. Warmer shades of white, yellow, or orange bulbs are less disruptive to humans and animals than cooler white or blue lights.
- Controlled: Use dimmable and control-ready lighting to save energy and minimize light pollution. Respond to seasonal environmental changes and adjust lighting levels accordingly.
- Limit shorter wavelength light: Reduce the use of shorter wavelength (blue-violet) light to the minimum amount necessary. Blue-rich white light can increase glare, disrupt the circadian rhythm, and have negative health impacts.
By following these principles, we can help reduce light pollution and create a better quality of life for all living things.
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Frequently asked questions
Light pollution is the presence of artificial light in otherwise dark conditions. It is a side-effect of industrial civilization, with sources including building exterior and interior lighting, advertising, streetlights, and illuminated sporting venues.
Light pollution has a range of adverse consequences, including:
- Eclipsing natural starlight
- Disrupting ecosystems
- Causing adverse health effects in humans, such as sleep deprivation, increased anxiety, and increased blood sugar levels
- Disrupting the circadian rhythms of humans and wildlife
- Causing light trespass, where unwanted light enters someone's property
You can start by completing a lighting assessment of your home to evaluate the need, function, and design of your lighting. You can also refer to the Bortle Scale, which is used by astronomers to measure sky brightness.
The proliferation of solid-state lighting and the changes to source spectral power distribution are key contributors to light pollution. The use of artificial lighting is increasing by 20% each year, with light pollution now affecting 83% of the global population.
Light pollution can be reduced by choosing responsible outdoor lighting. This includes using compact fluorescent lamps (CFLs) and LED bulbs that produce warm white lighting, using shielded light fixtures, and selecting fixtures with cutoff angles to prevent light from escaping above the horizontal plane.
