• Global light pollution has increased by 49% over 25 years to 2017, new research shows, and the real figure may be even higher.
  • Its impacts are wide-ranging - with human health, the environment and nature all affected, according to studies.
  • Immediate measures should be taken to limit artificial light at night in main cities and inside houses, say experts.

Affecting wildlife, biodiversity, human health and global energy efficiency, light pollution is at the apex of some of the most pressing global issues. What’s more, scientists say it’s getting worse.

What is light pollution?

While a broadly accepted definition of light pollution is the light generated by human activity that makes it difficult to see things in the sky at night, there’s a growing body of evidence that suggests the impact goes beyond merely blocking the potential for stargazing.

How dark the night sky is affects wildlife including bats, migratory birds and insects. Light pollution threatens the health and natural cycles of humans, as well as wastes energy and money.

An infographic explaining the disadvantages of light pollution
Light pollution has increased by at least 49% over 25 years.
Image: International Dark-Sky Association

How have levels of light pollution evolved?

Global light pollution has increased by at least 49% over the 25 years to 2017, new research shows and, because of the way it is measured, the real figure may be even higher than that.

Once an estimate for light-emitting diode, or LED, technology – which isn’t detectable to existing satellite sensors – is included, the increase in radiance in the visible spectrum may be as high as 270% globally, and 400% for specific regions, the study shows. It also concluded that there is little evidence to suggest that advances in technology have led to decreased light emissions.

“The global spread of artificial light is eroding the natural night-time environment,” said first author Dr Alejandro Sánchez de Miguel, of the Environment and Sustainability Institute on Exeter's Penryn Campus in Cornwall. “This study provides clear evidence not only of how bad light pollution has become as a global problem, but also that it is continuing to get worse, and probably at a faster and faster rate.”

Other studies show similar results, with an analysis of satellite data from 2012 to 2016 revealing that the total area lit by artificial light at night increased by 2.2% per year.

Why is light pollution a problem?

The consequences of light pollution are wide-ranging and can pose serious risks to many aspects of life on Earth. Here are a few of the associations that are proven or under investigation:

1. Light pollution interrupts wildlife patterns and harms biodiversity

Birds, bats and insects are among those in the natural world affected by light pollution, studies show.

Migratory birds rely on natural light to guide them and interruptions can lead to collisions and incorrect navigations on their long-distance journeys.

Artificial light disrupts nocturnal moths and may have reduced the number of caterpillars by half, according to another study. This has knock-on implications for those that feed on them. It can also tamper with the habits and reproductive cycles of bats.

The patterns and habits of other animals that are active at night - including owls, badgers, mice and frogs - are also affected.

2. Light pollution is associated with risks to human health

Humans are not exempt from the effect artificial light has on animals, with studies showing that it sends the body’s biological clock off, hampering sleeping cycles.

What’s worse, artificial light was found in a study to be “significantly correlated for all forms of cancer” including lung, breast, colorectal and prostate cancers individually.

“Immediate measures should be taken to limit artificial light at night in the main cities around the world and also inside houses,” the authors of one study wrote.

3. Light at night wastes energy and money, contributing to climate change

Conserving energy is one of the easiest ways to combat climate change. Leaving artificial lights on - for example in offices or stores after hours - is called “over illumination” and curbing it is one of the easiest ways to cut back on light pollution and save energy.

A European Commission study showed that city lights decrease the nighttime cleansing of the atmosphere, and reduce the ways nitrogen oxides are removed.

So what can we do about light pollution?

The good news is that light pollution is reversible - and this sets it apart from many other forms of pollution.


So what steps can be taken? The International Dark-Sky Association has the following tips:

1. Reduce the use of light, installing it only where it’s really needed and at the lowest brightness possible

2. Use controls like dimmers, timers and motion sensors to make the lights as efficient as possible

3. Use shields to direct light toward the ground, reducing glare

4. Use warm colour lights where possible and limit the use of blue wavelength lights, which are thought to be the most disruptive.

"Unlike many other environmental issues facing the world, solving light pollution is straightforward, saves money, and delivers immediate results," says Ruskin Hartley, Executive Director at International Dark-Sky Association.

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