Street lamps and the like are increasingly being equipped with energy-saving white light-emitting diodes. As a result, artificial light in Europe has increasingly shifted towards the bluish spectrum over the past ten years, a study shows. The extent of this trend is now becoming clear for the first time from evaluations of photos taken by astronauts on the ISS, which also show radiation components that have not been recorded before. The scientists emphasize that nocturnal light pollution and above all the increased blue component can have a negative effect on people and nature.
Where once only the moon and stars shimmered, street lamps and other human sources of light are turning night into day in many places. However, the brightness that we find helpful and often pleasant has its price: artificial lighting not only consumes a lot of energy, it can also upset the biorhythms of humans and animals and, above all, damage insects with fatal attraction forces. In this context one speaks of light pollution. It is particularly impressive when viewed from space: the densely populated areas of the world in particular shimmer at night.
Satellite imagery has also been used to study the extent and development trends of artificial nighttime lighting. However, as the researchers led by Alejandro Sánchez de Miguel from the University of Exeter report, there is a problem: so far, most studies that have examined the extent and effects of artificial night light have been based on data from satellite sensors, which have a broad range of data Capture the light spectrum, but not an important frequency range: the blue part in the range from 380 to 450 nanometers.
So far limited spectral view
However, these radiation areas are known to have particularly negative effects on the biorhythm and animal orientation. In addition, it was already assumed that the bluish components in light pollution were increasing. In order to save energy, in recent years many places have switched from conventional light sources to lighting with a "broad white" spectrum using light-emitting diodes (LEDs), which emit more short-wave radiation.
Since previous satellite images could only give limited indications of the extent of light pollution, de Miguel and his colleagues used an alternative that seemed unusual: photos taken by astronauts from the ISS with their digital cameras. As the researchers explain, these recordings also contain information about the low-frequency radiation ranges. "We used a synthetic photometry approach to estimate the spectral properties of the sources from the color relationships in the photographic images," the researchers write. They focused on nocturnal images of Europa made by astronauts from 2012-2013 and 2014-2020.
Underestimated blueshift trend
As the researchers report, their maps now document the trend in artificial lighting in Europe in detail for the first time: At the beginning of the time period under investigation, a radiation profile emerges that is still comparatively closely associated with conventional lighting, which often emanates from high-pressure sodium vapor lamps . In the course, a widespread spectral shift to the profile that is typical for the white glowing LEDs and the associated stronger blue emissions then becomes apparent. This trend was particularly pronounced in Italy, Romania, Ireland and Great Britain, the researchers report. In Germany and Austria, on the other hand, comparatively small changes were recorded. According to the scientists, this reflects the previously less pronounced conversion to LED lighting in public spaces.
One might think that the switch to more economical lighting technology would at least save energy. However, according to the researchers, it is becoming apparent that this is not the case. Because light generation and thus probably ultimately energy consumption have increased in many places in the course of the changeover. One possible explanation for this is a "rebound effect", the researchers write: the increase in energy efficiency and the associated supposed drop in economic costs have led to an increased demand for lighting. The bottom line was that any savings from increased light consumption were nullified.
Ultimately, exposure to light pollution has increased as Europe has switched to new lighting, the researchers said. Their results now show above all that this trend has been significantly underestimated up to now due to the limited spectral detection possibilities of the satellite sensors. On the basis of previous investigations, the scientists show again in their study how negatively the increasing exposure to more and more bluish artificial light can affect people and nature.
Your approach could now help to capture the development of the problem more precisely. “Systematic, high-resolution, multispectral satellite images for the night would be ideal. But until they are available, images from the ISS can provide a unique resource for monitoring and mapping environmental risks from light pollution,” the researchers write.