U.S. city lights outshine those in Germany when seen from space
German cities at night appear in satellite images as darker than U.S. cities of similar size, according to a new study.
The study, appearing in a recent publication of the journal Remote Sensing, found German cities emit several times less light per capita than comparably sized cities in the United States.
The research team gathered data for 28,804 U.S. cities and 4,492 German cities using the VIIRS instrument (Visible Infrared Imaging Radiometer Suite Day-Night Band) on the Suomi NPP (National Polar-orbiting Partnership) satellite. The pictures were taken at a resolution of about 750 metres, starting about two years ago.
"The size of the difference in light emission is surprisingly large," said lead author Dr. Christopher Kyba of Potsdam's German Research Centre for Geosciences. The study found a typical U.S. city with 100,000 inhabitants is five times brighter than a typical German city with the same population. Chicago and Los Angeles, as examples, were found to have an SOL (sum of lights) per capita that was nine and 3.5 times larger than Berlin, respectively.
The size of the gap grew with city size, with light per capita increasing with city size in the United States but decreasing with city size in Germany. In other words, larger American cities are brighter per capita than smaller towns, while the reverse is the case for Germany.
In addition, newer cities and subdivisions, notably those in the American West, tend to have younger and less abundant tree cover, which could obscure artificial lights.
"A final possibility is that German streets may be simply less brightly lit than American streets," said the study. It did not address what kind of lighting the two countries rely on the most, but said the the findings could be useful in other studies on light pollution, energy consumption and the epidemiology of illness related to light exposure.