How Light Pollution Impacts Our Night Vision

Light pollution is the human-made alteration of outdoor light levels from those occurring naturally. It has harmful effects on wildlife, ecosystems, energy and climate change, and human health. The excess or inappropriate artificial light outdoors obscures our view of the natural night sky, and can make stars and planets impossible to see. Light pollution also prevents the human eye from fully dark-adapting and reaching its maximum sensitivity. It tends to be most acute in urban environments, but it can also be perceived in remote or otherwise dark environments.

Light pollution and human health

Light pollution is the human-made alteration of outdoor light levels from those occurring naturally. It has been linked to harmful effects on human health. Research suggests that artificial light at night can negatively impact human health, increasing the risks of obesity, depression, sleep disorders, diabetes, breast cancer, and more.

Circadian Rhythm and Melatonin

Like most life on Earth, humans follow a circadian rhythm – a sleep-wake pattern governed by the natural day/night cycle. This cycle is largely influenced by photoreceptors in the eye that are more sensitive to blue wavelengths of light. Exposure to artificial light at night can disrupt this cycle.

Nighttime exposure to artificial light also suppresses melatonin production, which is necessary for maintaining health. Melatonin has antioxidant properties, induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes, and adrenal glands.

Not All Artificial Light is Equal

Exposure to any light at night can suppress melatonin, but photoreceptors in the eyes that drive this suppression are more sensitive to blue light. Most LEDs used for outdoor lighting, as well as computer screens, TVs, and other electronic displays, create abundant blue light.

Glare from Outdoor Lighting

Glare from poorly shielded outdoor lighting can also harm human health by decreasing vision through reduced contrast. This limits our ability to see potential dangers at night, especially for aging eyes.

Practical Ways to Reduce Light Pollution

• Full shielding: Prevent luminaires from sending any light directly at and above the horizontal, especially at low elevations.
• Limiting the area of lighting: Avoid wasting downward light flux outside the area that needs to be lit.
• Eliminate over-lighting: Avoid luminances or illuminances greater than what is required for the task, and dim lights when possible.
• Shut off lights when not in use: Turn off lights when leaving a room, or use automatic timers.
• Limit growth in installed lighting: Implement limits on the increase of new installed flux.

Light pollution and wildlife

Light pollution has a significant impact on wildlife, affecting the behaviours and survival of many different species.

Plants and animals have evolved to rely on the Earth's natural cycle of light and dark to govern essential life-sustaining behaviours such as reproduction, nourishment, sleep, and protection from predators. Light pollution disrupts this cycle, and can have deadly consequences for many creatures, including amphibians, birds, mammals, insects, and plants.

Effects on Wildlife

Amphibians

Glare from artificial lights can impact wetland habitats that are home to amphibians such as frogs and toads. Their nighttime croaking is part of their breeding ritual, and artificial lights can disrupt this activity, interfering with reproduction and reducing populations. Artificial lights can also attract frogs, making them more susceptible to dehydration and predators, as well as dangers such as roads.

Birds

Birds that migrate or hunt at night rely on moonlight and starlight to navigate. Artificial light can cause them to wander off course and towards dangerous, illuminated structures in cities. Millions of birds die each year from collisions with buildings and towers. Migratory birds also depend on properly timed seasonal schedules, and artificial lights can cause them to migrate too early or too late, causing them to miss ideal climate conditions for nesting and foraging.

Insects

Many insects are drawn to light, and artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination. Some predators exploit this attraction, affecting food webs in unanticipated ways. Artificial light can also disrupt the movement, foraging, reproduction, and predation of insects.

Mammals

Research has found that artificial light affects the behaviour of many mammals. For example, small mammals like mice eat less in lit areas to avoid predators, while their predators, such as foxes, are attracted to these areas for easy prey. Artificial light has also been shown to affect the circadian rhythm of some mammals, extending the day for diurnal species and shortening the day for nocturnal ones.

Reptiles

Sea turtles are one of the most well-known species affected by light pollution. Female turtles nest on beaches, and hatchlings instinctively head towards the brightest light on the horizon, which in natural conditions, would be the moon and starlight reflecting off the ocean. However, with coastal cities illuminating the night with bright lights, the hatchlings become disoriented and head towards the cities instead of the sea, falling prey to dehydration and predators. Artificial lights can also attract adult female turtles, causing them to waste valuable energy and risk being struck by vehicles.

Mitigation Strategies

To mitigate the impacts of light pollution on wildlife, it is recommended to use fully shielded, light-efficient fixtures that prevent light from escaping and causing unwanted illumination. Implementing wildlife-friendly lighting designs and managing light sources near protected wildlife areas are also important considerations. Additionally, nature-based solutions that balance wildlife conservation and human safety are crucial to addressing this issue.

Light trespass

A number of US cities have developed standards for outdoor lighting to protect their citizens against light trespass. The International Dark-Sky Association has also developed a set of model lighting ordinances to assist cities in this effort. Additionally, US federal agencies may enforce standards and process complaints within their areas of jurisdiction. For example, the Federal Communications Commission maintains an Antenna Structure Registration database that citizens can use to identify offending structures and process complaints.

To address light trespass, it is recommended to use shielded light fixtures that direct light more accurately towards where it is needed, with fewer side effects. This can be achieved by using full cutoff lighting fixtures, which reduce the chance of light escaping above the horizontal plane.

Sky glow

The phenomenon is often exemplified by the 'light dome', a visible effect of skyglow caused by artificial light sources illuminating the night sky. Areas affected by skyglow will show a grey-white or orange sky instead of remaining pitch-black. In extreme cases, the sky may even appear slightly yellow. This glow makes it harder to recognise and distinguish stars and planets, or they may not be visible at all.

Light used for all purposes in both outdoor and indoor environments contributes to artificial skyglow. Both the intentional and unintentional use of light, such as from lampposts, fixtures, and building illumination, contribute to the scattering of light into the atmosphere. Some of this light is then scattered back towards the ground, causing skyglow.

Skyglow is significantly amplified by the presence of snow, and clouds within and near urban areas. In remote areas, snow brightens the sky, but clouds make the sky darker.

Skyglow is a prime problem for astronomers, as it reduces the contrast in the night sky, making it impossible to see all but the brightest stars. The presence of skyglow means that people who live in or near urban areas see thousands fewer stars than in an unpolluted sky, and commonly cannot see the Milky Way.

The effects of skyglow on the ecosystem have been observed to be detrimental to a variety of organisms. The lives of plants and animals are affected as their natural environment becomes subjected to unnatural changes. Skyglow may interfere with trees' ability to detect seasonal changes and increase their chances of being killed by an early frost.

Additionally, many species of birds and sea turtles instinctively follow the moon's glow to guide their migration patterns. Skyglow makes this halo less noticeable, causing them to get lost. Insects and small animals are also attracted to areas with more light, and as skyglow attracts them towards cities and suburbs, they may find their way onto highways.

Light pollution and astronomy

Light pollution is a serious threat to astronomy and stargazing. It is the human-made alteration of outdoor light levels from those occurring naturally, and it has harmful effects on wildlife, energy consumption, climate change, and human health.

The proliferation of artificial light at night means that most people can no longer experience truly dark nights. Light pollution lightens the whole background of the sky, drowning out the dimmest stars and making it more difficult to see the brighter ones. This is due to light from poorly designed or incorrectly directed light fixtures, which shines into the sky and is scattered by air molecules, moisture, and aerosols in the atmosphere. This phenomenon is known as "sky glow".

Light pollution is worsening globally, and it is erasing stars from the night sky in many locations. More than 80% of the world's population currently lives under light-polluted skies, and this is increasing at a rate of almost 10% each year. The sales of LEDs, which emit large amounts of blue light that scatters widely in the Earth's atmosphere and deteriorates the quality of telescope observations, have also increased in recent years.

The effects of light pollution extend beyond astronomy. It has been shown to impact human health, including an increased risk of sleep disorders, obesity, depression, diabetes, and breast cancer. Light pollution also disrupts the circadian rhythm, the 24-hour day/night cycle that affects physiological processes in almost all organisms, including brain wave patterns, hormone production, cell regulation, and other biological activities.

Additionally, light pollution has negative consequences for wildlife and ecosystems. For example, sea turtles are affected by artificial light on beaches, which can disorient them and lead them away from the ocean. Birds are also impacted, as bright lights can confuse them during migration.

To preserve stargazing opportunities and mitigate the negative effects of light pollution, it is important to reduce the amount of artificial light at night. This can be done by turning off lights when they are not in use, shielding lights to direct them downward, and supporting dark sky ordinances in communities.

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