Red is the new black for night sky

Washington -  The colour of night-time skyglow may be about to undergo a radical change worldwide, suggest scientists of the Freie Universitat Berlin and the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Germany. 

The team predicted that with increasing use of LED street lamps, the colour of the night sky would become bluer.

To track this change, the researchers developed a prototype measurement device, and used it to show that the sky currently contains far more red light on cloudy nights compared to clear nights.

Christopher Kyba, physicist at the Freie Universitat and lead author of the study, explained that innovations in lighting technology would result in changes in the colour of streetlights.

“The current worldwide trend of replacing gas discharge lamps with solid state lighting, such as LEDs, will affect the radiance and spectrum of urban skyglow,” he said.

In order to understand the potential impacts of this change on ecology, it will be essential to monitor the sky over the long term.

The scientists developed a prototype measurement device and used it to study how clouds affect sky brightness in urban areas.

“For almost all of evolutionary history, clouds made the night sky darker, just like they do in daytime,” said Franz Holker, ecologist at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, study author, and leader of the project “Verlust der Nacht” (Loss of the Night).

In areas with artificial light the effect of clouds is now reversed, and the size of the effect depends on colour. The researchers found that in Berlin the blue portion of skyglow is 7 times more radiant on cloudy nights than on clear, and 18 times more for the red part.

In the visual range used by most animals, the researchers said that cloudy skies are now thousands of times more radiant near cities than they were throughout most of history.

They expect that the addition of this extra light affects predator-prey relationships where the predator hunts using vision, for example between owls and mice.

Their report has been published in the journal Monthly Notices of the Royal Astronomical Society.