European nights are getting bluer. In addition to a sharp increase in light pollution from nighttime artificial light, there is a shift from red-orange outdoor lighting to bluer light. Researchers conclude this based on photos of astronauts Their findings appeared on Wednesday in Science Advances.
The color shift indicates that more and more countries are using energy-efficient LED bulbs. Their light is often bluer than that of traditional lamps. “Our research shows that light pollution is increasing, including where it appeared to be declining according to previous measurements,” said astrophysicist Alejandro Sánchez de Miguel of the University of Exeter. This is because almost all previous research into nighttime artificial light has been done with satellite measurements and the satellite sensors used are blind to the blue light.
Sánchez de Miguel and his colleagues had long suspected that the increase in nighttime artificial light was greater. For example, light pollution in the United Kingdom, for example, seemed to be decreasing, while that was not the case. So they decided to look at color photos taken by astronauts from the International Space Station.
From warm red to cold blue
The researchers compared photos of European nights in 2012 and 2013 with those in 2014 to 2020. They then saw the color of the emitted light shift from warm red to cold blue. This effect is most evident in the United Kingdom, Italy and Romania. This is where the use of LED lamps has increased most. Sánchez de Miguel: “Milan was the first major city in Europe to completely replace its street lighting with LEDs, and in the United Kingdom, at the beginning of 2019, more than 50 percent of all public street lighting consisted of LEDs.”
The Netherlands, Germany, Austria and Belgium seem more conservative; there the color changed less between 2012 and 2020. Belgium in particular has a striking orange glow. There are still many low-pressure sodium lamps.
Artificial light has negative consequences for nature
Kamiel Spoelstra biologist
Both the increase in nighttime artificial light and the shift to bluer light are a cause for concern to the researcher. “Light pollution not only means that we hardly see any stars at night,” says Sánchez de Miguel. “Artificial light, especially blue light, has negative consequences for nature and human health.”
Kamiel Spoelstra, biologist at the Netherlands Institute of Ecology (NIOO-KNAW), agrees: “For example, the biological clock of humans and animals reacts relatively strongly to blue light, which can disrupt the sleep rhythm. And the eyes of animals that are active at night, such as mice, are adapted to the relatively blue background light at night. If outdoor lighting becomes bluer, they experience the ambient light more intensely, making them feel less safe because they are easier prey.”
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According to Sánchez de Migue and Spoelstra, less or no outdoor lighting would be best. And if lighting is needed, opt for warm white light that is a bit redder. This is also possible with LEDs. The cold, white LED light with a relatively large amount of blue is often slightly more energy-efficient, but you can also create warmer, redder LED light. Spoelstra: “Perhaps people should also learn to be less dependent on light.”