The brightness of the night sky has increased by an average of 10 percent each year, according to new research. That’s a significantly higher number than estimates made using satellite data — putting that figure closer to a 2 percent annual increase.
In other words, light pollution — which makes sleep and many daily tasks more difficult for humans and other living things — has been deteriorating much faster than expected. And just as LED lighting has become popular around the world, the satellites typically used to measure light pollution have not been able to fully track it.
At the rate at which we now know that light pollution has increased – a result of human light pollution – the brightness of the night sky is doubling approximately every eight years. A child born in a place where 250 stars are visible at night would be able to see only 100 of those stars at age 18.
Tens of thousands of individual stargazers around the world contributed to the discovery, which was published yesterday in the journal Science. The citizen scientists were able to make up for the blind spot of satellites when it comes to LEDs, which have come to be a major contributor to the problem.
A child born in a place where 250 stars are visible at night would be able to see only 100 of those stars at age 18
The discrepancy has to do with the inability of older satellites to accommodate LED lights that have become common in the past decade. LEDs save money and energy, so they have replaced more inefficient light bulbs in many places. They’ve also flooded more outdoor locations with light that used to go unlit at night due to the relative affordability of the technology.
But older generations of LEDs tended to emit light that falls in the blue end of the spectrum (although it’s often marketed as “white” light), which spreads across our sky more effectively. In addition, those “white” LEDs have shorter wavelengths that older satellites fail to detect.
On the other hand, humans are more sensitive to those shorter wavelengths than longer wavelengths of more orange light. The new paper is based on 51,351 citizen scientist observations made between 2011 and 2022 through a National Science Foundation program called “Globe at Night.”
The program asked people to rate the brightness of the sky by comparing what they saw at night to star charts. However, the study collected more data from North America and Europe than other regions. That means it could actually be underestimating the problem, because it lacks information from economically developing countries where light pollution is steadily increasing.
There are many different ways that pollution affects life on Earth, including humans. Bright light can mess with our sleep hormone melatonin. And there are many documented negative health effects associated with less peaceful sleep, such as an increased risk of chronic disease.
Artificial light can also interfere with pollination by potentially distracting or deterring insects, which can harm agriculture. Some birds navigate by starlight, which is harder to see in a clear night sky. Light pollution makes it harder for fireflies to send signals to each other with their own light, and it can pacify coyotes — which howl loudest during the dark skies of a new moon.
There are relatively easy ways to deal with those kinds of problems caused by too much bright light at night. Motion sensors can dim or turn off lights when no one is around to need them. Newer LED bulbs that aren’t as blue can replace the older generation bulbs. The UK even saw a reduction in light pollution during the pandemic as offices kept their lights off at night. And newer generations of satellites might better track the world’s light pollution. While we know what to do, the action just hasn’t kept up with the speed and magnitude of the problem, the new study shows.
People need to rethink our awe of city lights, write physicists Fabio Falchi and Salvador Bará in a related article commenting on the new research published in Science. “They don’t see that these are images of pollution,” says the newspaper. “It’s like admiring the beauty of the rainbow colors gasoline produces in water and not recognizing that it’s chemical pollution.”