Five years of advanced satellite images show that there is more artificial light at night across the globe, and that light at night is getting brighter. The rate of growth is approximately two percent each year in both the amount of areas lit and the radiance of the light.
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.
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 scientists 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.
“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.
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.
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.”
The British Journal Editors and Wire Services