Nighttime lighting in urban areas is a real nightmare for nocturnal animal species that are sensitive to light pollution.
A Wall of Nighttime Lighting
Indeed, the vast majority of cities, if they have not eliminated nighttime lighting or at least reduced its intensity to a minimum in the most natural areas, light their streets at night with LEDs whose white light is a true ordeal for these species.
Among the species on the front line of this wall of nocturnal lighting are, of course, bats. Whether it’s the common pipistrelle (Pipistrellus pipistrellus) or the brown long-eared bat (Plecotus auritus), these flying mammals are highly sensitive to short wavelengths (blue and UV). Result: white LED lighting, rich in blue light, literally saturates their retinal receptors. This makes them easy prey for natural predators, such as the long-eared owl and the common kestrel.
Red Monochromatic LEDs
Recently, a municipality on the outskirts of Copenhagen, Denmark, conceived a simple yet smart idea to help save their lives and the night: replace white lighting with red public lighting. Thus, one of the main arteries leaving the city center, Frederiksborgvej, now features red lighting.
It is an almost unprecedented experiment in adapting the city’s rules to the animal world, and not the other way around, for once. The light from the new streetlights, equipped with red monochromatic LEDs, concentrates only on wavelengths above 620 nm. Since bats lack photoreceptors sensitive to long wavelengths, they will hardly perceive this light anymore.
A European Program
Thus, instead of being somehow confined by light in an open space along the roadside, they will once again be able to return to their roosts or hunting grounds, reclaiming the freedom that urban lighting had blocked up to now.
Another benefit of such lighting, by the way, is helping to reduce the city’s energy consumption. This urban initiative is part of the European program Lighting Metropolis – Green Mobility. A cross-border project spanning eastern Denmark and southern Sweden. Its aim: to position this region as a global leader in smart lighting and sustainable mobility.
