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Artificial light sources can be deadly traps for insects that are active at night: They circle round the lamps until they die of exhaustion. Can reducing the duration or the brightness of the street lighting help to keep down the losses? How does this influence insect-hunting bats? WSL biologists working with Janine Bolliger tested this with the help of the EKZ (Elektrizitätswerk des Kantons Zürich EKZ), Canton Zürich’s municipal electricity utility, who installed sensor-controlled LED street lighting in Urdorf und Regensdorf. When no cars are driving past, the lamps automatically dim their light by about two thirds.
Less light means fewer victims
During the pilot phase in the summer of 2017, the lighting system was set to alternate at weekly intervals between dimmed and full lighting. Traps were mounted on the LED lamps to catch flying insects while a recording device registered bat calls. Early each morning a WSL staff member collected the insects.
It was the weather – in particular the temperature and precipitation – that was found to largely determine the number of ‘night lovers’. But dimming the lighting also had an effect: the number of trapped insects and bat calls dropped to half those with full lighting. Bugs, moths and hymenopterae are especially sensitive to light at night, whereas flies, mosquitoes and beetles are less affected. For bats, usually only the most common species benefited from the well-laden table around the lamps, while more sensitive species did not venture into the light. Janine’s conclusion: “Dimming street lamps and leaving them on for shorter periods of time can help to make well-lit streets less harmful for creatures active at night.” (Beate Kittl, Diagonal 1/18)