Our species seems programmed to love the light and fear the dark. But like sugar and screen time, too much light can be harmful – for ourselves and the other living things it touches.
Our ancestors made use of nighttime skyscapes to orient their lives: the position of the stars and moon helped some navigate across oceans and told others when to try their luck at fishing or put crops in the ground.
Yet today, most of that information – and that source of connection to cosmological and biological cycles – is hidden from many of us.
Over 80 percent of the world’s population lives under light-polluted skies. A third of us can’t see the Milky Way from where we live. (Use this interactive map or the Blue Marble navigator to see just how bright your town looks from above).
And all that glow and glare is getting worse: the average night got 9.6 percent brighter per year from 2011 to 2022 – essentially doubling the sky’s brightness every eight years.
Light pollution is the excessive or misdirected artificial light produced by human activity, which brightens the night sky and disrupts natural cycles of light and dark. It encompasses various forms, including:
The brightening of the night sky over inhabited areas, caused by the scattering of artificial light by dust and gas particles in the atmosphere.
Excessive brightness that causes visual discomfort or impairs vision.
Unwanted or intrusive light that spills beyond its intended target, such as into neighboring properties or natural habitats.
An excess of unnecessary, overly bright or poorly directed light sources.
All this extra light impacts our bodies’ circadian rhythms – our internal 24-hour body clocks that tell us when it’s time to wake, eat, sleep, digest and more.
Light at night lowers the production of the ‘sleep hormone’ melatonin, resulting in health impacts such as sleep deprivation, impaired memory, obesity and increased cancer risk.
Not all light impacts us equally. Many of us know intuitively how different it feels to walk into a blue-lit room to one with a yellow or ‘warm white’ light.
And science is backing that up: blue light, which is the most common kind emitted by cellphones and computers, as well as in LEDs (popular for their low cost and energy efficiency), has been shown to particularly impact human melatonin levels.
Many animals, especially nocturnal ones, are also thrown out of kilter by light pollution.
Migratory creatures, for instance, often rely on moon- and starlight to guide their way and can become confused by multiple light sources.
Hatchling sea turtles have been recorded confusing the glow of street lights with the moon over the sea – and heading for the highway instead of the ocean, with grim consequences.
Atlantic salmon fry exposed to street lights are hatching out of sync with each other, exposing them to predation.
Cook’s petrels (tītī, Pterodroma cookii) are fledging from a forested island off New Zealand, all set to travel thousands of kilometers to the North Pacific Ocean. But instead, they set off for the bright lights of nearby Auckland, where they’re vulnerable to cats, dogs and cars.
Meanwhile, many insects are drawn to light sources and die on contact with hot bulbs. Insectivorous bats, in turn, are attracted to the insects buzzing around bulbs, where they often make well-lit prey for their own predators.
Fireflies, for their part, are having less sex – and thus fewer offspring – in brightly-lit areas, because females can’t see males’ luminescent courtship signals with all of the electric competition.
Plants are also impacted by light pollution, which causes some to grow too much, while others disappear due to light impacts on pollinators.
Deciduous trees growing under street lights, for instance, hold onto their leaves a lot longer than they would otherwise, and they’re also budding earlier in spring. Grasses may also flower for longer under lots of light, extending hay fever seasons.
Many animals, especially nocturnal ones, are also thrown out of kilter by light pollution.
Migratory creatures, for instance, often rely on moon- and starlight to guide their way and can become confused by multiple light sources.
Hatchling sea turtles have been recorded confusing the glow of street lights with the moon over the sea – and heading for the highway instead of the ocean, with grim consequences.
Atlantic salmon fry exposed to street lights are hatching out of sync with each other, exposing them to predation.
Cook’s petrels (tītī, Pterodroma cookii) are fledging from a forested island off New Zealand, all set to travel thousands of kilometers to the North Pacific Ocean. But instead, they set off for the bright lights of nearby Auckland, where they’re vulnerable to cats, dogs and cars.
Meanwhile, many insects are drawn to light sources and die on contact with hot bulbs. Insectivorous bats, in turn, are attracted to the insects buzzing around bulbs, where they often make well-lit prey for their own predators.
Fireflies, for their part, are having less sex – and thus fewer offspring – in brightly-lit areas, because females can’t see males’ luminescent courtship signals with all of the electric competition.
Plants are also impacted by light pollution, which causes some to grow too much, while others disappear due to light impacts on pollinators.
Deciduous trees growing under street lights, for instance, hold onto their leaves a lot longer than they would otherwise, and they’re also budding earlier in spring. Grasses may also flower for longer under lots of light, extending hay fever seasons.
As the planet has become artificially brighter, there is growing awareness of the problem and attempts to mitigate it.
The global dark-sky movement began in the 1980s with the founding of the International Dark Sky Association (IDSA), which works to restore nighttime environments and protect communities from the harmful effects of light pollution through outreach, advocacy and conservation.
One of its efforts in this regard is promoting and certifying International Dark Sky Places that preserve and protect dark sites through responsible lighting policies and public education. There are currently over 160,000 square kilometers of protected land and night skies in 22 countries on six continents, and the list is growing every year.
In 2020, the Pacific Island nation of Niue was designated the world’s first ‘dark sky nation.’ It’s made an island-wide commitment to tracking light levels and replacing all of the country’s street and domestic lighting with orange bulbs – a move facilitated by the country’s small size and tiny population of just 1,600.
Try finding your home and comparing it to Niue, the world’s first ‘dark sky nation.’ What’s the difference in light pollution?
Proponents hope this will help protect the habits and health of key nocturnal native species such as the seed-dispersing Pacific flying fox (Pteropus tonganus tonganus) and the coconut crab (Birgus latro), which is a prized traditional food source.
But they also warn that efforts to conserve night skies in the Global South must be careful to ensure they don’t become neocolonial in nature. Instead, they should continue to make space for communities to pursue economic development as they see fit.
Safety is another consideration for people seeking to change light levels in urban areas, though it doesn’t necessarily play out the way you might imagine.
It’s a common assumption that brighter lighting correlates to greater safety, especially for women and girls walking at night in urban areas where sexual harassment and gender violence are prevalent.
Yet a 2019 study of the most unsafe ‘hotspots’ identified by women in Melbourne, Australia, found that “high illuminance – or very bright and overlit spaces – does not correlate with young women’s perceptions of urban safety.”
In fact, places with higher light levels were more likely to be perceived as unsafe because the glare and contrast meant it was difficult to see who was coming, and the sharp shadows left key areas obscured from view.
So, what can planners, regulators and residents do to bring our love affair with light back into balance?
A recent review outlines five key strategies to reduce lighting globally without compromising its benefits. These include:
A big part of changing nighttime skyscapes for the better is simply employing better planning so that we’re not sending wasted electricity up into the sky. The following diagram shows an example of smart street lighting – and its more-polluting counterparts.
So, on the bright (or indeed, dark?!) side, light pollution is one of the few environmental issues for which the solutions are relatively clear, simple, and inexpensive.
The night sky is one of the very few natural resources that’s “100 percent restorable,” said Bob Meadows, a physical scientist with the U.S. National Park Service, in a 2022 Grist article.
“We’re just masking our ability to see it and experience it.”
Text by: Monica Evans
Illustrations and design by: Inês Mateus
Produced by: Eden Flaherty
