Human Health

Exposure to Light Pollution Harms Your Health

Research suggests that light pollution negatively effects human health, increasing risks for obesity, depression, sleep disorders, diabetes, breast cancer and more.

Many species (including humans) need darkness to survive and thrive.

— American Medical Association Council on Science and Public Health (2012)

Circadian Rhythm and Melatonin

Like most life on Earth, humans have a biological clock called your circadian rhythm. It is a sleep-wake pattern governed by the day-night cycle. Artificial light at night disrupts that cycle.

Our bodies produce the hormone melatonin in response to our circadian rhythm. Melatonin helps keep us healthy. It induces sleep, boosts the immune system, lowers cholesterol, and helps the functioning of the thyroid, pancreas, ovaries, testes and adrenal glands. Nighttime exposure to light pollution suppresses melatonin production.

Blue Light is the Most Harmful Type of Light Pollution

Exposure to blue light at night is harmful. Unfortunately, most LEDs used for outdoor lighting — as well as computer screens, TVs, and other electronic displays — have a white colour which is dominated by blues.

According to experts at Harvard Medical School,

“If blue light does have adverse health effects, then environmental concerns, and the quest for energy-efficient lighting, could be at odds with personal health. ”

A 2016 American Medical Association report expressed concern about exposure to blue light from outdoor lighting and recommends shielding all light fixtures and only using lighting with 3000K colour temperature and below.

To minimize harm from blue light in your home, choose the right light bulb and download a colour temperature app that adapts your electronic screen to the time of day – cool light during the day and warm light at night.

Colour Temperature Apps:

  • F.lux is available for Mac OS/X, Windows, Linx and (jailbroken) iPhones and iPads.
  • For those with Apple devices using the iOS 9.3 operating system and above, the Night Shift app is pre-installed. Click here to learn how to use it. 
  • Lux is available for Android devices free or for pay.
  • Twilight is available for smartphones or tablets.

Choosing the Right Bulb

ColorTemp

In this picture both lights are “white” but the bulb on the left is rich in blue light, while the one on the right isn’t. The warmer light on the right is the better, healthier one to choose.

All packaging for new light bulbs provides colour temperature information. Use low-colour temperature light sources for interior and exterior light. Their light is less harsh and less harmful to human health and the environment. Look for warm white sources with a colour temperature of 3000K or lower.

Kelvin Temperature Scale

Higher colour temperatures mean white light that is more blue-ish and less warm, the kind that should be avoided after dusk.

3 types of light bulbs showing different effects of colour temperatures.
Image: Wikipedia, shows three different white lights with blue, yellow and orange tints to them. The orange 2700K light is the healthiest and most environmentally positive type to chose.

Glare from Bad Lighting is a Safety Hazard

Glare from poorly shielded outdoor lighting is also harmful to your health because it decreases vision by reducing contrast. This limits our ability to see potential dangers at night. Ageing eyes are especially affected.

“Glare from nighttime lighting can create hazards ranging from discomfort to frank disability.”

American Medical Association Council on Science and Public Health (2012)

Measuring Light Pollution

Jesus Acosta, the impact of light pollution as seen during a power outage.

Due to light pollution, the night sky over many of our cities is hundreds of times brighter than a natural, starlit sky. This skyglow hides the stars from our sight and prevents us and all life on Earth from experiencing a natural night, even in areas hundreds of miles away from towns and cities.

How can you help?

Lincoln cathedral at night
Lincoln Cathedral. Image: Mark McNeill

Become a Citizen Scientist

The CPRE does an annual star count which you can do from your back garden or yard. Anyone can take part in it, and you don’t need specialist training or equipment. Find out more here.

Participating in the Globe at Night citizen-science campaign is a great way to help our understanding of skyglow and its impact. No special tools are required and observations can easily be reported by smartphone, tablet or computer.

It’s also possible to use your smartphone to make night sky brightness measurements. The Dark Sky Meter app makes use of the iPhone camera to record the brightness of the night sky, while the Loss of the Night app walks the user through the sky as measurements are made with a different sensitive tool – the human eye. It’s available for both Android devices and iPhones. And now, thanks to the MySkyatNight project, you can also do your own analysis of all this available data.

Jodrell Bank under a starry sky but with some light pollution showing in the background
Jodrell Bank under a starry but light polluted sky. Image: Mark McNeill

Another way you can help is by participating in the Cities at Night project, which relies on citizen scientists to map and identify photos of cities taken from the International Space Station. This valuable information helps researchers better assess light pollution across of the globe.

In addition to the smartphone apps and the Globe at Night project, more rigorous, long-term monitoring is also being conducted. The section below describes standards for collecting and reporting skyglow measurements.

How Can You Help With Skyglow Observations?

The introduction of the Sky Quality Meter and the International Year of Astronomy Lightmeter have led to a large number of permanent online skyglow monitoring stations. At the same time, a number of individuals and groups have developed their own non-commercial devices for measuring skyglow.

If there is a dark sky park or reserve near you, they are always on the lookout for volunteers to help them with their dark sky measurements.

a before and after picture showing how bad lighting can be improved using IDA guidelines
a before and after picture showing how bad lighting can be improved using DarkSky guidelines. Image: DarkSky

Wildlife & Ecosystems

For billions of years, all life has relied on Earth’s predictable rhythm of day and night. It’s encoded in the DNA of all plants and animals. Humans have radically disrupted this cycle by lighting up the night.

When we add light to the environment, that has the potential to disrupt habitat, just like running a bulldozer over the landscape can.”

— Chad Moore, formerly of the National Park Service

Plants and animals depend on Earth’s daily cycle of light and dark rhythm to govern life-sustaining behaviours such as reproduction, nourishment, sleep and protection from predators.

Scientific evidence suggests that artificial light at night has negative and deadly effects on many creatures including amphibians, birds, mammals, insects and plants.

Artificial Lights Disrupt the World’s Ecosystems

Nocturnal animals sleep during the day and are active at night. Light pollution radically alters their nighttime environment by turning night into day.

According to research scientist Christopher Kyba, for nocturnal animals,

“the introduction of artificial light probably represents the most drastic change human beings have made to their environment.”

“Predators use light to hunt, and prey species use darkness as cover,” Kyba explains “Near cities, cloudy skies are now hundreds, or even thousands of times brighter than they were 200 years ago. We are only beginning to learn what a drastic effect this has had on nocturnal ecology.”

Chris Kyba

Glare from artificial lights can also impact wetland habitats that are home to amphibians such as frogs and toads, whose nighttime croaking is part of the breeding ritual. Artificial lights disrupt this nocturnal activity, interfering with reproduction and reducing populations.

Artificial Lights Can Lead Baby Sea turtles to their Demise

Sea turtles live in the ocean but hatch at night on the beach. Hatchlings find the sea by detecting the bright horizon over the ocean. Artificial lights draw them away from the ocean. In Florida alone, millions of hatchlings die this way every year.

Artificial Lights have Devastating Effects on Many Bird Species

Photo by Michael Menefee

Birds that migrate or hunt at night navigate by moonlight and starlight. Artificial light can cause them to wander off course and toward the dangerous nighttime landscapes of cities. Every year millions of birds die colliding with needlessly illuminated buildings and towers. Migratory birds depend on cues from properly timed seasonal schedules. Artificial lights can cause them to migrate too early or too late and miss ideal climate conditions for nesting, foraging and other behaviours.

Ecosystems: Everything is Connected

a 15 second exposure showing the behaviour of insects around artificial lights. Image: Nevit Dilman It is dark and there is a streetlight attracting insects to it. Because it is a long exposure you can see the trails the insects make as they travel towards and around the light.
a 15 second exposure showing the behaviour of insects around artificial lights. Image: Nevit Dilman

Many insects are drawn to light, but 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 to their advantage, affecting food webs in unanticipated ways.

Energy Waste

Lighting that emits too much light or shines when and where it’s not needed is wasteful. Wasting energy has huge economic and environmental consequences.

In an average year in the U.S. alone, outdoor lighting uses about 120 terawatt-hours of energy, mostly to illuminate streets and parking lots. That’s enough energy to meet New York City’s total electricity needs for two years! We estimate that at least 30 percent of all outdoor lighting in the U.S. alone is wasted, mostly by lights that aren’t shielded. That adds up to £3 billion and the release of 21 million tons of carbon dioxide per year! To offset all that carbon dioxide, we’d have to plant 875 million trees annually.

Environmental responsibility requires energy efficiency and conservation

  • Installing quality outdoor lighting could cut energy use by 60–70 percent, save billions of £££ and cut carbon emissions.
  • Outdoor lighting should be fully shielded and direct light down where it is needed, not shining up into the sky.
  • Unnecessary indoor lighting – particularly in empty office buildings at night – should be turned off.

New lighting technologies can help conserve energy

  • LEDs and compact fluorescents (CFLs) can help reduce energy use and protect the environment, but only warm-white bulbs should be used. Learn more about LEDs and colour temperature from our LED Practical Guide.
  • Dimmers, motion sensors and timers can help to reduce average illumination levels and save even more energy.

Quality lighting design reduces energy use and therefore energy dependence. It also reduces carbon emissions, saves money and allows us to enjoy the night sky. Watch a clip of the documentary The City Dark to learn how lighting design can reduce light pollution and also conserve energy.