Light pollution is now among the most chronic environmental perturbations on Earth. In 2016 scientists estimated that 99 percent of the continental United States and Europe suffer some amount of light pollution.
Their study found that a third of humankind—including nearly 80 percent of North Americans—cannot see the Milky Way. And data from the Suomi NPP satellite suggest that worldwide, light pollution increased by roughly 2 percent a year from 2012 to 2016.
All lights, but especially LEDs, are to blame. Because they’re much more energy-efficient than incandescent and CFL bulbs, LED lights are left on for longer periods, casting cheap light in all directions.