An experiment conducted in Germany demonstrated that lamps emitting warm light attract significantly fewer insects compared to cold light sources. Over two years, the study was carried out at six railway stations located within a nature park. The results showed that replacing cold lamps with warm ones reduced the mortality of nocturnal flying insects caused by artificial lighting by about half.

Global Decline in Insect Populations

In recent decades, there has been a significant decrease in arthropod populations worldwide. For example, a 2017 study in Germany recorded a 75% drop in the biomass of flying insects over 27 years. Similar trends have been confirmed in other countries as well. The mass disappearance of insects could lead to the loss of pollinators, the collapse of food chains, and disruptions in ecosystem functioning.

The main causes of insect decline are considered to be the use of pesticides and the loss of natural habitats. Another contributing factor is artificial night lighting (ALAN), which disrupts the orientation of insects such as moths and beetles that use the moon and stars for navigation. Streetlights can disorient them, causing them to circle the light source for extended periods, which leads to exhaustion and death.

The Impact of Light Spectrum on Insects

Cold white light with a temperature of around 4000 Kelvin, which contains short-wavelength blue light, is considered the most harmful to insects, as their compound eyes are especially sensitive to this spectrum.

The study tested three types of lamps: high-pressure sodium lamps (HPS, 2000 K), standard white LEDs (4000 K), and experimental amber-colored LEDs with a reduced blue spectrum (1800 K). A total of 36 insect traps were installed on the platforms, which automatically opened only at night to exclude daytime species.

Experimental Results

The analysis showed that warm LEDs (1800 K) attracted 45% fewer insects in the first year of the experiment compared to standard white lamps (4000 K): an average of 96 versus 175 insects per trap per week. In the second year, the difference increased to 51%—25 versus 51 insects—and the biomass of attracted insects dropped nearly fourfold.

Older yellow-orange sodium lamps (HPS), despite their low color temperature, proved to be just as attractive to insects as cold white LEDs. This is because sodium lamps generate significant heat, which attracts blood-sucking insects such as mosquitoes.

Conclusions and Practical Measures

The experiment confirmed that the mass mortality of nocturnal insects can be significantly reduced by adjusting the emission spectrum of streetlights. As a result of the study, new warm-colored lighting fixtures have already been installed at the six railway platforms.