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This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., The nighttime is undergoing unprecedented change across much of the world, with natural light cycles altered by the introduction of artificial light emissions. Here we review the extent and dynamics of artificial light at night (ALAN), the benefits that ALAN provides, the environmental costs ALAN creates, approaches to mitigating these negative effects, and how costs are likely to change in the future. We particularly highlight the consequences of the increasingly widespread use of light-emitting diode (LED) technology for new lighting installations and to retrofit pre-existing ones. Although this has been characterized as a technological lighting revolution, it also constitutes a revolution in the environmental costs and impacts of ALAN, particularly because the LEDs commonly used for outdoor lighting have significant emissions at the blue wavelengths to which many biological responses are particularly sensitive. It is clear that a very different approach to the use of artificial lighting is required. © 2022 by Annual Reviews., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

We are grateful to C. Whelan and the two anonymous reviewers for helpful comments. KJG and DTCC were supported by the Fragments, Functions and Flows in Urban Ecosystems project (no. NE/J015237/1) funded under the Natural Environment Research Council (NERC) Biodiversity and Ecosystem Services Sustainability (BESS) thematic program,and DG was supported by grant no. CGL2015-68963-C2-2-R (MinECo).

A large body of work over the past few decades has revealed the manifestly dramatic impacts of urbanization on species’ distributions and ecologies, many of which result from gross changes in land use and configuration. Less well understood are the rather more direct interactions between people and biodiversity in the urban arena. While there is a general concern that urbanization impoverishes human contact with nature, daily interaction with biodiversity in urban greenspaces and the widespread provision of food and nesting resources for wildlife form a part of many city-dwellers’ experience. Using data from the UK, we show that supplementary resource provision aimed explicitly at enhancing avian populations can result in high levels of additional foraging and nesting opportunities, particularly in urban areas. However, our data also indicate that levels of such resource provision are strongly positively correlated with human population density at a regional scale, and within a large city. The proportion of households participating in bird feeding depends on social and economic features of the human population, suggesting that strong covariation between human and ecological communities will result. Indeed, we demonstrate that the abundances of some urban-adapted bird species are positively related to the density of feeding stations across the urban landscape, although such relationships were not apparent for other species that commonly use garden feeding stations. It has been suggested that interactions with nature, such as feeding birds, could have beneficial consequences for human health. A better understanding of this potential feedback is required.