Quickly airing the room in summer evenings without turning off the light can attract myriads of insects. Specially moths soon enter a spiralling path around the light. But why is that so?

Nocturnal insects like moths us the moon for their orientation. Keeping themselves in a certain angle to it helps them fly straight. This technique works because the heavenly light source is very far away. Artificial luminaires are closer and consequently during the insects´ flight their angle changes constantly. The permanent course correction ends in a spiral which takes the moth dangerously close to the light source and eventually makes it collide with it. Scientists call this explanation navigation theory – for it has not been finally clarified in detail yet.

Also the color of light affects the insects´ approach. Warm white light of LED attract less animals than for example mercury high-pressure lamps which nowadays are rarely used. Learn more in issue licht.wissen 20 “Sustainable Lighting”.