Our night sky is getting brighter and brighter — not because of the moon, but due to artificial lighting.
While outdoor lighting is a necessary part of modern society, its widespread use has reshaped natural darkness, affected human and animal health and made the night sky harder to see.
According to a new study that analyzed a combination of satellite images, artificial nighttime lights have brightened Earth by 16% between 2014 and 2022. Researchers from University of Connecticut found that nights are gradually becoming brighter worldwide, though trends vary by region, particularly in areas affected by war or natural disasters. The findings were published in Nature.
In 2022, the United States had by far the highest total luminosity of any country, followed by China, India, Canada and Brazil.
“For decades, we’ve held a simplified view that the Earth at night is just getting steadily brighter as human population and economies grow,” said senior author of the study Zhe Zhu, director of the University of Connecticut’s Global Environmental Remote Sensing Laboratory. “The planet’s lighting footprint is constantly expanding, contracting and shifting,” Zhu said.
The glow: Earth’s light pollution
In the United States, nearly 80% of people reside in urban areas. In many locations, the brightness of artificial light sources obscures the beauty of the night sky. Due to city lights, only the brightest stars, planets and other celestial objects are visible, according to DarkSky International, a nonprofit organization dedicated to protecting night skies.
In the Nature study, researchers also identified areas where artificial light levels had decreased. This dimming was attributed to the Russia–Ukraine conflict in 2022, which triggered a regional energy crisis and caused European nights to darken dramatically.
Built from a decade of daily NASA satellite imagery, the image below compares 2012 with 2023 and highlights shifts in human nighttime activity.
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What is light pollution?
Excessive artificial lighting outside is known as light pollution and according to DarkSky, there are four ways that light pollution can happen:
- Glare: The intense, uncomfortable light that shines directly at the viewer and obstructs their eyesight.
- Skyglow: The brightening of the night sky due to light distributed in the atmosphere by human-caused lighting.
- Light trespass: Unwanted artificial light spilling onto another person’s property or space, such as light from a streetlight shining in a bedroom window.
- Clutter: Intensely bright lights, which cause visual discomfort. Common examples include extremely bright streetlights or poorly aimed spotlights.
How much light pollution is in your area?
Excessive lighting is a common feature of cities, suburbs and urban towns. These light sources include parking lots, streetlights, advertisements and both internal and outdoor lighting.
The brightness of the night sky can be measured by using the Bortle scale. The scale has nine levels, with Class 9 representing the highest level of light pollution.
To easily check for artificial light pollution in where you live, visiting the Light Pollution Map to gauge the amount of light is near you.
How too much light can impact wildlife and humans
Both animals and humans are affected by artificial light.
In animals, research shows that light pollution disrupts a wide range of behaviors, including migration patterns, sleep–wake cycles and habitat development. Species that rely on natural light cues are particularly vulnerable.
According to DarkSky International, sea turtles and birds use moonlight to navigate during migration. Artificial lighting can disorient them, causing them to stray from their routes and often leading to death.
Artificial lights also attract large numbers of insects, which are a primary food source for birds and other animals. Many of these insects are quickly killed when they come into contact with light sources, reducing available food and further disrupting ecosystems.
For humans, artificial light at night can disrupt the body’s natural circadian rhythm by suppressing melatonin, a hormone that helps regulate sleep; this disruption may in turn interfere with biological processes such as hormone regulation, cell growth and DNA repair that help protect against cancer.
In a 2024 peer reviewed study published in ScienceDirect, researchers found that higher exposure to outdoor artificial light at night (ALAN) was associated with a modestly higher risk of breast cancer.
Save energy: Things you can do to help lessen light pollution
The good part of light pollution is that it is entirely reversible. Anyone is capable of making a difference by using these easy light-dimming tips:
For additional tips to help reduce light pollution, visit DarkSky.org.
SOURCE Nature, NASA, Reuters, DarkSky International, National Park Service, Space.com and USA TODAY research
CONTRIBIUTING Ramon Padilla/USA TODAY
This story has been updated to fix punctuation.
