Analysing 86 sites across North America and Europe, scientists found that artificial light at night (ALAN) led to higher ecosystem respiration — meaning plants, microbes, and animals emitted more carbon dioxide — without any increase in photosynthesis to balance it.

"Brighter nights lead to greater carbon release, which is bad news for our planet," said Dr. Alice Johnston of Cranfield University, the study's lead author. The findings suggest that light pollution is altering the "fundamental energetic constraints" of natural ecosystems.

Researchers argue that light pollution is one of the easiest environmental problems to fix. "Unlike climate change, we could reduce light pollution almost overnight with better lighting design," Johnston said, calling for dimmable, directional, and spectrally sensitive lighting. Since lighting accounts for over 15% of global electricity use, such measures would also reduce energy demand.

Co-author Professor Jim Harris warned that a quarter of Earth's land surface now experiences artificial illumination at night, potentially shifting the global carbon balance "if left unaddressed."

While some European countries — including France, Croatia, Slovenia, and the Czech Republic — have national laws limiting light pollution, regulation remains fragmented. Initiatives like the International Dark Sky Places programme are helping protect naturally dark areas, from Cévennes National Park in France to Rhön Biosphere Reserve in Germany.

Experts say addressing light pollution offers a "rare win–win–win" — improving environmental health, energy efficiency, and human wellbeing simultaneously.