Light pollution has emerged as a burgeoning area of scientific interest, receiving increasing attention in recent years. The resulting body of literature has revealed a diverse array of species-specific and context-dependent responses to artificial light at night (ALAN). Because predicting and generalizing community-level effects is difficult, our current comprehension of the ecological impacts of light pollution on complex ecological systems remains notably limited. It is critical to better understand ALAN's effects at higher levels of ecological organization in order to comprehend and mitigate the repercussions of ALAN on ecosystem functioning and stability amidst ongoing global change. This theme issue seeks to explore the effects of light pollution on complex ecological systems, by bridging various realms and scaling up from individual processes and functions to communities and networks. Through this integrated approach, this collection aims to shed light on the intricate interplay between light pollution, ecological dynamics and humans in a world increasingly impacted by anthropogenic lighting. This article is part of the theme issue 'Light pollution in complex ecological systems'.