Mitigating light pollution impacts on arthropods based on light-emitting diode properties.

Light pollution from artificial light at night (ALAN) is a significant environmental problem with far-reaching consequences for ecological systems. Recent innovations in light-emitting diode (LED) technology may offer sustainable outdoor lighting solutions, but scientific evidence is lacking. We investigated the effects of various LED lighting properties (color temperature, light intensity, and luminaire shape), individually and in combination, on flight-active and ground-dwelling arthropods. We therefore conducted a field experiment at 3 forest field sites in Switzerland with standardized LED streetlights. Over the course of 3 summers, we monitored flight-active insects and ground-dwelling arthropods with automated flight-interception and pitfall traps. The absence of light reduced the number of arthropods caught by 91%. However, when lighting was necessary, dimming lights by 50% and using focused luminaires resulted in reductions of 22% and 42%, respectively. Light color influenced arthropod responses only when combined with dimming. Our results underscore the ecological benefits of darkness and the complex interactions among lighting properties. An optimized combination of these properties, particularly well-focused and dimmed LED luminaires, represents a practical and effective measure to reduce the ecological impacts of ALAN and promote the conservation of nocturnal species.