Germany's nights are getting brighter - partly

Light pollution increases almost everywhere - only in Th ringen it gets darker

Satellite image of Central Europe at night - light pollution is increasing almost everywhere © NASA / SVS
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The light pollution in Germany is increasing - but not everywhere: While the nights have become much brighter in most federal states since 2012, the nocturnal flare in Thuringia has even decreased. Whether this is due to a conversion to LED lamps or actually reflects a decrease in lighting, is so far unclear. By contrast, light pollution has risen particularly sharply in Bavaria and Schleswig-Holstein, as new satellite data show.

Man turns night into day: Lighting the streets, buildings and industrial facilities in many places does not make it dark even at night. 80 percent of humanity live in an abnormally bright night sky. This light pollution not only hinders the observation of the sky, it also disturbs the internal clock of humans and animals. However, despite the negative consequences of the nighttime scattered light continues to increase in most regions, as satellite data show.

Almost everywhere the nights get brighter

How light pollution has developed in Germany has now been determined by Christopher Kyba from the German Geo-Research Center Potsdam (GFZ) and his colleagues. They evaluated data from a special photometer on board the Suomi NPP weather satellite. For the period from 2012 to 2017, they recorded changes in the brightness of the upward scattered nightlight as well as changes in the illuminated area in the individual federal states.

The result: In many parts of Germany, light pollution is following the global trend: Both the illuminated area and the intensity of the scattered light have increased in recent years. This was particularly dramatic in Bavaria and Schleswig-Holstein. There, the illuminated area has grown by 45 and 40 percent since 2012, the brightness of the scattered light increased by 35 and 41 percent, as the researchers report.

Changes in illuminated area and brightness in the various federal states. Kyba et al./GFZ

Only thuringia gets darker

But there are big regional differences: especially with the increase in illuminated areas, there is a clear East-West difference. In all the new federal states, including Berlin, the artificially lit areas are almost the same. Here, light pollution has increased on average by less than one percent per year, as determined by Kyba and his colleagues. display

Particularly striking is a "dark" Ausrei er: Th ringen. In this state, the next ones have evidently even become darker instead of brighter. "Th ringen is dramatically different from the rest of the region, " the researchers report. "Here, the illuminated area has decreased by 18 percent and the brightness by 17 percent.

Are the LED lamps guilty?

What is behind it? The increase in night lighting in most parts of Germany led Kyba and his team back to the increased use of LED lights. These are often brighter than older street lamp sodium vapor lamps, and because they consume less power, more of them are often installed.

However, the researchers have so far no clear explanation for the decrease in brightness in Th ringen. You can only speculate. "Perhaps the data shows that the sodium vapor lamps, which are still widely used there, are aging and fading, " Kyba speculates. But it could also be that municipalities in Th ringen converted more consistently to LED. Because their blue light spectrum is only partially captured by the satellite sensor, such areas may appear darker. "We just need more data, " says Kyba.

Street lighting off at night?

He and his colleagues emphasize, however, that action against increasing light pollution is sensible and necessary. One measure could be to reduce street lighting after midnight, or even switch it off altogether. "Considering the few pedestrians and vehicles traveling in many smaller German locations after midnight, one should ask oneself whether continuous lighting is really necessary, " says Kyba.

Especially since such a temporary shutdown seems to have no negative effects: As the researchers report, a study in the UK has shown that even a complete shutdown of the street lamps after midnight neither increase the traffic accidents still the criminality. (International Journal of Sustainable Lighting, 2018; doi: 10.26607 / ijsl.v19i2.79)

(GFZ Potsdam, 26.02.2018 - NPO)