New road lights, fewer dead insects – insect-friendly lighting has been successfully tested

In a transdisciplinary study, an IGB-led research team developed insect-friendly street lighting and tested it in the Westhavelland dark sky reserve as well as in three German municipalities. Customized and shielded road lights make the light source almost invisible outside the illuminated area and greatly reduce the deadly attraction for flying insects in various environments. Scientists see this as an important engineering solution to reduce insect mortality.

The study was published in the journal Communication biology.

Road lights can become a trap for insects at night: Flying insects such as moths are attracted by the light and pulled from their habitats (vacuum cleaner effect). Disoriented insects often circle light sources until they die of exhaustion or are eaten.

In order to test insect-friendly road lighting, road lights in a field experiment in the Westhavelland dark sky reserve (AuBe project) and on roads in municipalities in Baden-Württemberg along three selected nature reserves in the Rhine-Neckar, Karlsruhe and Freudenstadt districts (NaturLicht project ) were converted in the before and after experiment. The four sites were chosen to represent a wide range of environmental conditions (urban, suburban, rural) and existing light pollution and cover a large area of ​​Germany.

Light only where needed is much better than dimming

The new LED fixtures provide more focused light, reduce stray light and are shielded above and on the sides to minimize light pollution. And they reduce insect mortality: Catches in insect traps on the lights showed the researchers that the number of attracted flying insects was significantly lower. Previous conventional lights were used as a control.

Surprisingly, dimming conventional lights by a factor of 5 had no significant effect on insect attraction. “In fact, we hypothesized a general dose-response relationship for insect flight behavior in relation to artificial light. However, it turns out that reducing unwanted light emissions using spatial confinement and shading is much more effective than reducing lighting,” explained the IGB researcher. Manuel Dietenberger, first author of the study.

The exact mechanism of how insects react to street lighting is not yet fully understood. It is thought that some insects do not fly directly towards the light for a short distance, but instead tilt their backs towards the brighter hemisphere to maintain flight control.

“Given the results, we therefore recommend the use of adapted and shielded luminaires to protect insects,” said Prof. Andreas Jechow from the Brandenburg University of Applied Sciences and visiting scientist from the IGB.

“This should be used especially in sensitive areas such as nearby nature reserves, freshwater ecosystems or other areas with high biodiversity,” added Franz Hölker, head of the IGB Light Pollution and Ecophysiology research group.