Artificial night-time lighting has widespread impacts on the natural world, according to a new paper published on 3 November in the journal Nature Ecology & Evolution (1). In particular, night-time lighting disrupts the hormone levels and waking and sleeping patterns of many species. Artificial lighting should therefore be treated as another pollutant and only used where and when it is needed, the authors say.
The team of biologists from the University of Exeter analysed more than 100 previously published papers to gain a deeper understanding of the effects of artificial light in terms of hormone levels, breeding cycles, activity patterns and vulnerability to predators across a broad range of species.
Previous studies have noted reduced pollination by insects, trees budding earlier in spring when exposed to artificial light. Rodents – which are mostly nocturnal – are also becoming less active at night, while daytime birds start singing and foraging earlier, and are active for longer.
The findings were not all negative as some species have benefited from night-time light. For example, bat species seem to thrive and some plant species grow faster. However, the overall effects appear to be “enormously disruptive”. All species exhibited reduced levels of melatonin – a hormone that promotes sleep – when exposed to artificial light.
The human illumination of the planet is increasing by two per cent each year and the problem is comparable to climate change, the authors say.
“Both climate change and night-time lighting are human-driven and enormously disruptive to the natural world”, said co-author Prof Kevin Gaston in a statement.
“Lots of studies have examined the impacts of artificial night-time lighting on particular species or communities of species”, Gaston explained. “Our research brings those studies together – and we find the effects are very diverse and very pervasive.”
“Particularly strong responses are seen in hormone levels, the timing of daily activity in diurnal (daytime) species, and ‘life-history’ traits such as number of offspring.”
“People may imagine this is all about powerful light, but in fact we are seeing a lot of responses at quite low levels of artificial light”.
Another problem is that more expensive soft amber bulbs are being increasingly replaced by cheaper and brighter white LEDs, which are even more detrimental from a biological perspective.
Fortunately, the problem is much easier to solve than climate change. While it may not be realistic to switch off all the lights, the authors suggest limiting the use of artificial lighting to places and times when it is genuinely required. Fewer lights would also mean less electricity is used, which would save money and reduce greenhouse gas emissions.
“Our study shows that we should, as a matter of principle, only use night-time lighting where we need it and no further, and at intensities that we need and no more,” said Gaston. “In effect, we need to view light like any other pollutant”.
(1) Sanders, D. et al. A meta-analysis of biological impacts of artificial light at night. Nature Ecology & Evolution (2020). DOI: 10.1038/s41559-020-01322-x