If you're thinking that it seems a little less dark at night these days … well, you might not be imagining things. According to a new study led by Dr. Christopher Kyba of the German Research Center for Geoscience, Earth's artificially lit outdoor areas grew in size and radiance by 2.2 percent per year – on average – from 2012 to 2016.
For the study, Kyba and his team analyzed data gathered by the space-based Visible Infrared Imaging Radiometer (VIIRS), comparing annual readings for different geographical regions over the four-year period. The VIIRS is installed on the NOAA (National Oceanic and Atmospheric Administration) satellite Suomi-NPP, and is the first such device designed specifically for imaging night-time lights.
Although the overall trend was definitely upward, changes in lighting intensity varied a lot by country, with developing nations leading the way. Particularly bright places like the US and Spain remained relatively stable over the four years, for instance, with larger increases occurring in most nations within South America, Africa and Asia.
Globally, it was found that increases in lighting corresponded closely to increases in the Gross Domestic Product. Lighting radiance decreased in only a few countries, such as Yemen and Syria, which are both in the midst of wars.
It should be noted that the VIIRS doesn't detect light at wavelengths below 500 nanometers. This "blue" light can be seen by people, and makes up a significant portion of the light given off by LED streetlights. Essentially, this means that as cities have replaced older orange streetlights with more efficient LED models, the radiometer may have detected a decrease in visible light that didn't really happen – at least, not as far as the human eye is concerned.
A paper on the research was recently published in the journal Science Advances.