Artificial light at night disrupts the behaviour, physiology, and ecology of nocturnal and twilight species. As light pollution spreads to cover 83% of the world population, its welfare impacts on wildlife have become increasingly significant.
Light pollution causes welfare harm through disruption of fundamental biological rhythms and behaviours. Sea turtle hatchlings that travel inland rather than to sea die of dehydration and exhaustion. Birds that fly into lit buildings experience trauma and death. Nocturnal animals that cannot forage effectively face nutritional stress. Insects attracted to lights die there in vast numbers. The welfare scale of light pollution is enormous: billions of insects and millions of birds are killed annually by artificial light in the US alone. Mitigation is technically straightforward — shielded downward-pointing lights, motion sensors, amber rather than blue wavelength LEDs, and switch-off policies for non-essential lighting. The welfare case for these relatively low-cost interventions is compelling.