City lights drive back the night a little more each year, disrupting ecological cycles. Now, energy-efficient lights could be making light pollution worse.

Earth's total artificial light at night brightened by at least 2.2 percent each year from 2012 to 2016, most notably in South America, Africa and Asia, according to satellite research published in the Nov. 22 edition of Science Advances.

Co-author Franz Hölker of the Leibniz Institute of Freshwater Ecology and Inland Fisheries said these lights place unprecedented stresses on plants and animals, including humans.

"It threatens biodiversity through changed night habits, such as reproduction or migration patterns, of many different species — insects, amphibians, fish, birds, bats and other animals," Hölker said.

The switch from orange-yellow sodium lights to bluish-white LEDs worsens the problem. Blue light scatters farther in the sky and is more harmful to insects and mammals.

That shift also means that the study likely underestimates artificial light emissions in areas lit by LEDs. The Visible Infrared Imaging Radiometer (VIIRS) satellite sensor used by the researchers only detects light in the 500-900 nanometer bands and therefore does not "see" blue light, which occurs at wavelengths below 500 nm.

The authors hypothesized that broad-scale efforts to save energy by transitioning to solid-state technologies like LEDs might be undercut by an economic rebound effect, in which lowered costs spur cities to add more lights.

The American Medical Association issued a health and safety warning last year concerning LED streetlights.

The authors said cities could possibly address these problems by using LEDs with their blue light component removed. They could also switch to true amber LEDs, which shine in a spectrum similar to low-pressure sodium lights and could be especially useful in areas of ecological concern.

Comparison of lighting changes in Calgary, Alberta, Canada in 2010 and 2015 using photos from the International Space Station.