Flying insects often use celestial cues, such as moonlight, to navigate during the night. Because the moon is consistently positioned above them, insects orient themselves so that the light shines on their backs to maintain upright flight. However, moonlight contains ultraviolet (UV) and infrared (IR) wavelengths because it is reflected sunlight. When artificial lights transmit UV, insects can mistake these sources for the moon, causing them to orient toward the light and circle it. This biological mechanism explains why traditional lighting has historically drawn massive swarms of insects.
The primary difference between older and newer lighting technologies lies in their spectral output. Incandescent bulbs, which use a tungsten filament, naturally transmit UV light. In contrast, light-emitting diodes (LEDs) are designed for energy efficiency, converting electrical energy almost entirely into the visible light spectrum (400–700 nm). Because LEDs generally do not emit UV wavelengths, they do not trigger the same navigational responses in insects. A 2016 study by the University of Bristol confirmed this, finding that LEDs attracted significantly fewer insects—including flies and midges—than incandescent or compact fluorescent lights. Interestingly, the study found no significant difference in attraction between 'cool-white' and 'warm-white' LED varieties.
This image illustrates the transition from traditional incandescent bulbs to modern LED technology discussed in the text.
This graph provides visual data supporting the study's findings on how different light types affect insect behavior.
This shift in lighting technology has potential ecological benefits. Because UV artificial light can distract insects and disrupt their natural behaviors, the move toward LED lighting may help mitigate disturbances to wildlife and reduce the occurrence of insect-borne diseases. However, the transition is not universal; some observers still report seeing moths and bees attracted to specific home LED setups. This suggests that while the absence of UV is a primary factor, individual bulb types, environmental variables, or specific light intensities may still influence insect behavior in different ways.