tl;dr: Insects are drawn to incandescent lights because they emit UV wavelengths that mimic moonlight, which flying insects use to orient themselves. LEDs convert energy almost entirely into visible light without UV emissions, making them far less attractive to insects—a 2016 University of Bristol study confirmed LEDs caught significantly fewer insects than incandescent or compact fluorescent bulbs. The widespread switch to LEDs may reduce ecological disruption to insect populations, though it also means fewer bugs (and the geckos that eat them) congregating around porch lights.