Typically, when people think about pollution, it’s a question of air quality. But there’s another kind that poses a threat to humans and animals: light pollution.

Multiple studies have shown that the abundant nighttime light found on streets and in buildings can adversely affect animals — altering migration patterns — as well as insects. There’s also been increasing evidence that it can disrupt the circadian rhythm of humans, an important biological process that regulates our sleep cycle.

For these reasons, many people have advocated finding ways to reduce light pollution. But it’s not always clear which sources are creating the most light. 

A recent study published in the journal Lighting Research & Technology examined streetlights in Tucson, Ariz., over a period of 10 days. The city dimmed the lights at 1:30 a.m. every day during that period. Using satellites to monitor the light that seeped upward into space, the study found that light pollution dropped by just 13 per cent, suggesting that there are other sources of light that are causing pollution. (They suspect it could be things like billboards, car dealerships and parking lots.)

The importance of the study is to illustrate that cities can conduct similar research to determine ways to reduce light pollution from sources other than streetlights, said Christopher Kyba, a scientist with the GFZ German Research Center for Geosciences in Potsdam, Germany, and lead author of the paper. Kyba acknowledges more research is needed to determine exactly where that excess light pollution comes from, something that he hopes to examine in another study.

Finding out more about this could help cities design strategies to address the issue. But there’s another benefit to reducing light pollution: less light means less energy production.

“All the light that we have is paid for by someone, and basically at the end of the day, it’s us,” said Kyba.

“We need the energy to produce all that light,” he said, which could mean building environmentally unfriendly structures like a nuclear power plant or a hydro dam. “Or you have to burn coal or something and we all know that’s bad for all kinds of reasons.”

Kyba said, “anything we can do to reduce energy consumption is basically alleviating this other problem associated with energy production.”

Robert Dick, former chair of the light pollution abatement committee at the Royal Astronomical Society of Canada, said light pollution should concern everyone.

“[People] should care about light pollution the same way they should care about reducing environmental pollution and designing cities to be sustainable,” he said. 

“Light pollution is one of those extra stressors you put on the environment.”