LED-technology increases light pollution across the night sky

Most people would have to travel quite a distance to see a szene like this: Somewhere, away from civilization, at a coast or in the mountains. Whereever there are humans, there are ever more artificial light sources. They make the skies brighter. The result: artificial lights outshine the stars. The stars fade and eventually disappear from view.

The newest generation of lamps doesn't consume much energy anymore. Therefore, people use more of them. And there is another effect: LED-lamps often contain more light with a cold blue wavelength. The glaring color intensifies light pollution.

The European Southern Observatory (ESO) is located in a specially protected zone in Chile. Here, it is forbidden to emit artificial light outside the house. The ESO is far from human settlements. But observatories near cities have to cope with light emissions. That's why these cities try to reduce light pollution by installing yellow and warm, rather than white and cold street lights.

Scientists of the German Research Center for Geosciences, the Leibnitz Institute and the universities of Exeter (UK) and Boulder (Colorado/US) used satellite data and pictures from the International Space Station to observe the changes. This is a view from the ISS of Calgary/Canada in 2010.

The same perspective in 2015. One can see that the lighting system has been changed in entire city districts. The light-color is now whiter. Some roads have been added as well. The radiometre that the scientists used could not properly measure the light intensity in the blue spectrum. This means that the light was even more intense than indicated by the collected data.

The instrument was a Visible Infrared Imaging Radiometer (VIIRS). Its resolution was 750 meters. The data showed that the intensity of artificial light from outside sources increased by an average of 2.2 percent from 2012 to 2016.

Globally, the increase in light was roughly aligned with the increase in gross domestic product for individual countries. The strongest increase in both fields could be detected in emerging economies.

Artificial light changes the lives of animals and plants. Birds living in cities are already changing their natural sleep patterns. Plants that are exposed to artificial light have an extended growth period.

The question remains: Do cities need to have their street lights on all night? Even though LEDs don't use much electricity, we may still switch them off if nobody needs them. Lights that are activated by movement could be a solution. And if nobody is around, a less bright emergency light would be enough.