Satellites show we are rapidly losing our night sky
Wednesday, November 22, 2017, 3:24 PM - According to a new study, light pollution is spreading around the world, taking even more of our night sky from us. The primary culprit? LED lights.
For the past five years, the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite has been orbiting Earth, taking images of both the day and night sides of the planet. While the day-side images have given us the ability to track weather, climate, pollution, dust, smoke, sea ice and other changes happening on the surface, the night-side images have revealed just how much artificial light we are producing, and how much light pollution is spreading.
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Now, a new study, published in the journal Science Advances, has taken all of Suomi NPP's night-side images from the past five years, and examined just how much artificial lighting has spread during that time.
The researchers found that both the amount of lit areas at night, and the brightness of the light, are increasing by roughly 2 per cent per year.
While that is understandable for cities, where continued urban development would cause light to spread, the study found that artificial light is increasing nearly everywhere, even in regions farthest from urban development, which are actually seeing the largest changes.
These maps show the rates of change of the lit areas of the world (left) and the measured brightness of each country (right), from 2012-2016. Warmer colors correspond to higher rates of change. Credit: Kyba et al./Science Advances
"Light is growing most rapidly in places that didn’t have a lot of light to start with," study lead Dr. Christopher Kyba, from the GFZ German Research Center for Geosciences in Potsdam, Germany, said in a press release. "That means that the fastest rates of increase are occurring in places that so far hadn’t been very strongly affected by light pollution."
One of the causes of this spread of light pollution is the global transition away from using outdoor incandescent and fluorescent lights, towards using LED lighting instead.
While LED lights are presented as being better for energy consumption, as they consume less energy to produce the same amount of light as other types of lightbulbs, they do produce more blue light than the other, older lighting methods.
Two nighttime images of Milan, Italy, taken by astronauts on the International Space Station in 2012 (left) and 2015 (centre), along with the amount of increase or decrease in brightness, expressed as a fraction, as measured by Suomi NPP's VIIRS Day-Night Band (right). This comparison captures how the lighting changed in the city core after it switched from using high-pressure sodium vapour lights to white LEDs. Credit: Kyba, et al./NASA
According to the study, Suomi NPP's Day-Night Band (DNB), which the satellite uses to take nighttime pictures of Earth's surface, does not pick up blue light (with wavelengths of between 400-500 nm) very well. So, even though the above images vividly reveal the transition between the yellow-orange high-pressure sodium vapour lights to white LED lights in Milan's city core, the Day-Night Band was unable to capture the corresponding increase in brightness from the new lights.
That increase in brightness would be much more noticable on the ground, both in the direct effect on our night-vision (from light sources that are within our direct line of sight), and in the increase in "skyglow" - the dome of light seen over large urban centres, caused by artificial outdoor light being scattered by the atmosphere.
Artificial outdoor lighting, especially from high-intensity LED lights, doesn't just affect our night vision. Studies have shown that artificial light (especially white LEDs) can disrupt our circadian rhythms, leading to health problems. Widespread artificial light can have a detrimental affect on wildlife as well.
This infographic shows the number of countries experiencing various rates of change of night lights during 2012-2016. Credit: Kyba et al./Science Advances
Another notable find by the study is that LED lights have not yet delivered on their promise of overall lower energy costs, around the world. In fact, the study found that any savings that did occur were immediately reinvested in producing more lights, thus cancelling out the savings.
This isn't to say that LED lights, themselves, are bad, or that we shouldn't put in the effort to make the transition. We simply have to be careful how we proceed.
"There is a potential for the solid-state lighting revolution to save energy and reduce light pollution," Kyba said, "but only if we don’t spend the savings on new light."