Artificial lights are obscuring the moon and stars, damaging human health, and disrupting the natural environment. Why is this a concern? And how can we address it without sitting in the dark?
A streetlamp directly in front of your home can make it safer to enter at night, but attempting to sleep without heavy curtains becomes a challenge. This is just one illustration of how artificial light serves many purposes in our daily lives while also posing a significant issue.
Our planet is bathed in more artificial light than ever before. A recent US study revealed that nighttime artificial light emissions rose by roughly 16% globally between 2014 and 2022, based on findings published in Nature.
Areas that experienced increased brightening also saw a rise in light intensity, averaging 9%.
Excessive artificial light can make us ill
We can turn off light sources like computers, phones, TVs, and lamps on our own. However, other sources are beyond our control: streetlights, car headlights, illuminated monuments, flashing billboards, and spotlights at construction sites, storefronts, bus stops, parking lots, sports fields, and stadiums, to name just a few.
Being exposed to artificial light to this degree can disrupt our natural sleep-wake cycle, upsetting our hormonal balance and raising the risk of metabolic disorders such as diabetes, depression, and obesity.
The color of light also matters. The colder or whiter the light, the more it mimics daylight—and the more it suppresses melatonin, the hormone that induces sleepiness in the evening.
No other environmental condition has remained as consistent over millennia as the natural light from the sun, moon, and stars. All living organisms have adapted to this rhythm. More than half of all species are nocturnal—if nights become brighter, it could have devastating effects.
Migratory birds rely on the moon and stars for navigation. Artificial light can distract and divert them from their paths, leading to detours and exhaustion. Other birds may be tricked into laying eggs too early in the season, when there aren't enough insects for newly hatched chicks to eat.
Insects like moths and beetles use starlight to find food and mates. But artificial lights are far brighter and inevitably lure them away. They circle the light source continuously until they collapse and die from exhaustion. Billions are killed this way each year, a devastating toll when insects are already threatened by pollution, declining biodiversity, and other dangers.
Nocturnal mammals such as hedgehogs and bats generally avoid well-lit areas; in our brighter world, their habitat is steadily shrinking. Light can also create an artificial barrier that some fish species refuse to cross. For example, lights cast on the water's surface from an overhead bridge can prevent eels from swimming past—a major issue during their migratory spawning period.
The world is too bright
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Brightest night skies in China, India
The Nature study found that the increase in nighttime light emissions since 2014 was highest in Asia, particularly in the economically growing regions of China and India.
In the United States, light pollution increased most on the West Coast due to the growing economy and population in California's cities. The East Coast and parts of the US Midwest, in contrast, have become darker—partly because of a shrinking industrial sector, fewer residents, and more energy-efficient lighting.
In Europe, overall light intensity compared to 2014 decreased by 4%, with researchers noting a drop in light pollution across the region as a whole. That decline was most pronounced in France (33%), the United Kingdom (22%), and the Netherlands (21%).
Unlike in the United States, darker night skies in Europe are not always due to economic decline.
In France, for instance, new bylaws now require lighting on all commercial buildings, storefronts, parking lots, public parks, and cultural heritage sites to be turned off by 1 a.m. at the latest.
Other European nations took on the issue of brightening night skies much earlier. The Czech Republic enacted the world's first law against light pollution in 2002, which stipulates, among other rules, that streetlights may only be directed toward the ground, with fines of over €3,000 ($3,500) for violations.
Slovenia has been combating light pollution since 2007, with a regulation limiting annual electricity consumption for lighting per resident to 50 kilowatt hours. Other rules also ensure that streetlights do not shine too brightly at night in residential areas.
Germany's 'star city,' Fulda, lights the way
Germany has yet to pass any nationwide rules against light pollution. The Federal Nature Conservation Act is, however, currently being updated in an effort to curb it. At the state level, Baden-Württemberg has already passed a law prohibiting facade illumination from April to September—the months when wildlife is most active in Germany.
The city of Fulda, about 100 kilometers (60 miles) northeast of Frankfurt, is a leader in lighting practices. The Fulda Cathedral is illuminated with precisely targeted spotlights instead of standard floodlights. In new neighborhoods outside the city center, walkways and cycle paths are lit to only 20%; when someone approaches, motion detectors briefly bring the streetlights to full brightness.
"Insect traps installed before and after these measures were implemented have shown that the new lights kill 90% fewer insects," said Marcel Cire, environmental engineer with Fulda's city planning department. He noted that Fulda is beginning to install the new streetlights in the city, replacing old lamps as needed to keep costs down.
Fulda has been recognized for its efforts to restore the night. DarkSky International, a US-based nonprofit raising awareness about the harmful effects of excessive artificial light, designated the city as Germany's first "star city" in 2019. It joined 11 other certified locations in the country with "outstanding dark sky conditions and protection practices."
Bringing back the firefly
As demonstrated in the Czech Republic, Slovenia, and Fulda, lights should only illuminate where absolutely necessary—for example, walkways, not the entire night sky. Lights regulated with motion sensors are a good alternative to always-on outdoor lighting.
The warmer the light, the less harmful it is—for humans and other creatures. Conservation organizations recommend using a light temperature of no more than 3000 Kelvin for outdoor lighting, a warm, yellow-white light commonly used in living rooms and bedrooms.
Following these recommendations could help bring fireflies back to our parks and gardens. The firefly is another insect threatened by light pollution, as artificial light prevents male and female insects from finding each other.
Simply closing the curtains in your house at night can help not only to block out annoying outdoor glare but also to prevent indoor light from disturbing the nightlife outdoors.
This article was originally written in German.