The analysis is based on several assumptions. The transparency of the atmosphere, how much light from cities goes upwards, the time of night, and the light spectrum are all variables that were set by the researchers, so the atlas might not always reproduce the real world correctly.
Even considering the potential uncertainties, the situation remains quite severe. Artificial light strongly influences our sleeping patterns and there are parts of the world, like Singapore, that never experience true night. Light pollution could not only stop us from seeing the sky, but it could be negatively affecting our health.
In particular, the reduction of blue light has been seen as a particularly important issue. Blue light boosts attention, reaction times, and mood, which is great during the day but not so much at night. To save energy, there has been a significant move towards LEDs, and while they are much better for the environment they emit a significant amount of blue light. If all street light were LEDs, the sky would become twice as bright.
While the study might not come across as very optimistic, the researchers suggest several ways to reduce and mitigate the effects, such as light shielding, turning off and limiting public lighting when not necessary, and a significant reduction of blue light emission from LEDs.
Speaking to IFLScience, lead author Falchi discussed what can be done to reduce light pollution. "In Italy cieloBuio Association was able to contact directly regional politicians and convince them of the opportunity to enforce laws against light pollution. In this way, at least, we got a stop in the increase of light pollution. We need, as for almost all other pollutants, to lower them with time, so we need to increase action. And the first step is to increase the awareness of the problem."
The Americas in New World Atlas of Artificial Sky Brightness, as seen in Google Earth. Provided by Fabio Falchi et al
Although a recent study showed no relation between lighting and road safety, some people still don't think living cities completely in the dark is safe.
"Most people think that lighting our environment as much as possible will lower crime and traffic accidents. But first of all these claims must be proven, before using them to spend billions of Euros annually to power public and private lighting," added Falchi. "For now the proof is missing."