LULU GARCIA-NAVARRO, HOST:
The world is getting brighter, which is not necessarily a good thing. Scientists say artificial light from cities and other human settlements across the world may have a negative impact on humans and animals. NPR's Nell Greenfieldboyce reports that researchers are now able to measure exactly how much brighter the globe gets each year.
NELL GREENFIELDBOYCE, BYLINE: Light pollution can keep people from seeing the stars. It might affect wildlife, like migrating birds. And Christopher Kyba says it just keeps increasing.
CHRISTOPHER KYBA: My mom, for example, grew up on a farm in Saskatchewan in a time before they had electrification. So she grew up with an amazing, starry sky. And now she lives within one lifetime under a very light-polluted sky.
GREENFIELDBOYCE: Kyba studies nighttime light at the German Research Center for Geosciences. He and some colleagues knew that a satellite launched in 2011 had a new instrument, one that gives scientists a more reliable way to measure how much brighter the world is getting. The research team looked at five years of data.
KYBA: And we saw an increase of an average of 2.2 percent per year, which is pretty close to 10 percent over the study period. That's globally.
GREENFIELDBOYCE: The night glow only decreased in war-torn countries like Syria, according to a report in the journal Science Advances. And the light increased the most quickly in developing countries.
KYBA: So a lot of places in South America, Africa and Asia are brightening really, really rapidly up to 10 percent or more per year even in some cases.
GREENFIELDBOYCE: The United States didn't show much change, but Kyba says lots of places in this country are switching to LEDs for light. And this satellite cannot detect all the kinds of light that LEDs put out.
KYBA: And that means that, actually, the United States is almost certainly getting brighter in terms of how people see the world with their human eyes.
GREENFIELDBOYCE: Kyba says what he'd like to see is more well-designed lighting that lets people on the ground feel comfortable and safe without needlessly lighting up the night sky. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.