Where the lights never go out
Heavily populated areas are losing the distinction between day and night, and that could mean health problems.
The distinction between day and night is disappearing in the most heavily populated regions of the Earth, a rapid shift with profound consequences for human health and the environment, according to a recent paper in the journal Science Advances.
“We’re losing more and more of the night on a planetary scale,” journal editor Kip Hodges said in a teleconference on the paper’s findings.
From 2012 to 2016, the artificially lit area of the Earth’s surface grew by 2.2 percent per year, according to the study led by Christopher Kyba of the German Research Centre for Geosciences. Kyba and his team analyzed high-resolution satellite imagery to measure the extent of artificial outdoor lighting at night. The study also found that areas of the planet already lit grew even brighter, increasing in luminosity at a rate of 2.2 percent per year.
“Earth’s night is getting brighter,” Kyba said. One of Kyba’s images shows the change in the amount of nighttime lighting from 2012 to 2016.
Much of the increase is concentrated in the Middle East and Asia. The observed “decrease” in western Australia is actually due to wildfires in 2012 that were visible from space.
These observations probably understate the true increase in lit areas and light intensity because the satellites used in the study are not sensitive to blue light wavelengths emitted by LED lights.
The trend shows no sign of relenting.
“In the near term, it appears that artificial light emission into the environment will continue to increase, further eroding Earth’s remaining land area that experiences natural day-night light cycles,” the paper concludes.
The past few years have seen the rapid adoption of highly efficient LED lights for indoor and outdoor use. LEDs use just a fraction of the electricity of traditional incandescent lights. .
But the rapid increase in nighttime lighting observed by Kyba and his colleagues suggests that people are responding to cheaper lighting options by simply adding more light.
“While we know that LEDs save energy in specific projects,” Kyba said at the teleconference, “when we look at our data and we look at the national and the global level, it indicates that these savings are being offset by either new or brighter lights in other places.”
The shift from incandescents to LEDs has been directly observable from space.
People are particularly attuned to the short-wavelength blue light emitted by most LEDs, but it’s been implicated in sleep deficiencies and other human health problems.
The news isn’t all bad. Studies have shown, for instance, that judicious use of low-level LED lighting can reduce light pollution without compromising peoples’ sense of safety.