A team of international researchers has found that, despite an increase in energy-efficient LED bulbs, surface light pollution has increased around the world.
That, they say, is due to the so-called rebound effect: lighting has become cheaper and more energy efficient, so people are using more lights more often.
While other studies have tackled the issue of light pollution, lead researcher Christopher Kyba, who is originally from Alberta and is now a physicist at the GFZ German Research Centre for Geosciences, said there is one key difference in this one: "We're looking down versus up."
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The researchers in the study, which was published Tuesday in the journal Science Advances, used data from the Visible Infrared Imager Radiometer Suit (VIIRS) aboard the Suomi-NPP satellite from 2012 to 2016 to study surface light pollution. The radiometer isn't sensitive to blue light — the colour put out by many LED lights — so Kyba expected to find a decrease in light detected.
'It's not just a problem of the west... we're really seeing it all over the world.' - John Barentine, International Dark-Sky Association
What he found surprised him.
"What I had expected to see was that in wealthy places countries — the United States, countries with a lot of lighting, Italy — cities were going to be changing to LED and that would make them look darker," Kyba said. "But it turns out the United States stayed flat, and other countries like Germany became brighter. That means that the increase is actually even larger than what we report here.
"Somewhere else, there's new light."
That new light likely comes from increased use, since it's cheaper.
Over the past four years, the artificially lit surface of Earth at night increased by two per cent annually, or 9.1 per cent in total.
John Barentine, program manager at the International Dark-Sky Association out of Tuscon, Ariz., said the findings aren't a surprise.
"It's not just a problem of the West... we're really seeing it all over the world," Barentine, who was not involved with the study, told CBC News.
"When something becomes less expensive to produce, we tend to use more of it than less," Barentine said. "Some of us had this suspicion that maybe all these cost savings of the better energy efficiency of lighting may just be ploughed back into buying more lighting...and that seems to be what's happening."
The study also found that the increase in light pollution corresponds to increasing gross domestic product (GDP): developing countries show the fastest growth.
Light pollution has been cited by several studies as a potential risk factor for various health issues, including cancer.
"I am concerned about the fact that we now have scientific evidence that the light at night and especially the white light [that contains blue by definition], is linked with many health issues like breast and prostate cancers and sleep disorders," Martin Aubé, who studies light pollution at Quebec's University of Sherbrooke and was not involved in the study, told CBC News. "Even if we know this, we still increase the amount of light at night."
Then there are the effects on wildlife: migratory birds that fly at night can be thrown off course. Many crash into illuminated buildings.
Light pollution has also disrupted the nesting habits and important sea-finding habits of turtles.
Both Kyba and Barentine believe the efficiency is what is causing not just people, but cities to use more lighting.
"Our suspicion to a large extent it's new uses of light that people may not have done in the past. And you see things like the bridge in Montreal," Kyba said. "In the '70s ... we wouldn't have thought to do that, because we'd think, 'That's crazy expensive!' But now it's like, you can do this amazing thing with LEDs. Why don't we just do it? It doesn't cost that much."
In 2016, Kyba was also part of a new world atlas that illustrated the brightness of the night sky. That study, published in the journal Science Advances, estimated the Milky Way is hidden from more than one-third of humanity.
But both Kyba and Barentine wonder if there's a better way to discourage lighting overuse.
"Before we did the study, I was hoping that things were getting darker ... because I thought the message was getting out there," Kyba said. "To some extent, I think it also shows that the very best way would be with a carbon tax."
Those who study light pollution are also looking at ways to improve lighting to make it more practical, including full cut-off lighting, more diffuse lighting and less blue light.
"I think we can provide for all the legitimate human needs for light at night ... in a way that doesn't result in all this excess light leaving in the form of pollution," Barentine said.