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Synthesis of Studies on the Effects of Artificial Light at Night

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1978-2019, with 2020 update

Project Summary

The Natural Resource Stewardship and Science Directorate (NRSS) develops, utilizes, and distributes the tools of natural and social science to help the National Park Service (NPS) fulfill its core mission: the protection of park resources and values. For scientific topics experiencing rapid growth in knowledge, producing a balanced summary of this knowledge is challenging, especially because the most recent articles may contain crucial, relevant information for management of resources and visitor experience. This project addresses the challenge of realizing balanced coverage through a stringent application of a systematic, comprehensive queries of the scientific literature.

Changes in the nocturnal environment– arising from expansion of human populations, transportation networks, and resource extraction activities– is a global issue1 with implications for human health and ecosystem integrity2 (Figure 1). Light presents diverse threats to species and ecosystems and important patters are emerging in the literature useful for resource management3. To provide relevant updates on existing literature documenting the effects of artificial light at night, this project summarizes the results from our systematic query of the literature. The intent is to provide park managers with an accessible perspective of the size and scope of the relevant scientific knowledge.

We emphasize the distinction between our approach and the results from an ad hoc query using Google Scholar or a related tool. Our query was developed and tested – by experts in the field – to ensure that the results encompassed all the relevant literature. This query was reviewed and improved in an iterative process. Though no query can guaranty it will capture every relevant paper; our current query delivers results that are far more comprehensive than our initial searches. We are confident that our present query is the best tool to identify the pertinent papers.

Four maps show growth in artificial sky brightness in Continental U.S. over time from 1950s, 1970s, 1997 and prediction in 2025. Night sky gets brighter through time and east coast brighter than the west.
Figure 1. Simulation of light pollution growth in the United States4.

Purpose of Brief

This resource brief represents a knowledge of light effects on wildlife and people in an accessible format. The focus here is on the size of the literature, the kinds of light sources that were studied, and the breadth of documented effects.

We believe the value of this brief to NPS managers is to raise awareness of the extent of scientific support for park planning and management, and identification of distinct subsets of this literature that may be of special relevance for specific locations or management actions. The authors will assist parks with more detailed and specific analyses of this literature upon request.

Finding Relevant Studies

We conducted a peer-reviewed literature search using Thompson’s ISI Web of Science (WOS). The search included papers published after 1977 to ensure all relevant literature was captured. The search was optimized to capture a known list of relevant studies. Ninety-two percent of the known studies were captured using our search criteria.

The final search for papers published between 1978-2018 resulted in 353 studies. We conducted additional searches following the same protocol in subsequent years up to and including this year 2020. All papers were reviewed by a subject matter expert such that only studies focused on documenting the effects of artificial light at night were included in the final data set (N = 316 relevant studies from 1978 to 2020). Papers that were not relevant included those that summarized light levels without documenting a response. For the papers deemed relevant, the subject matter expert labeled each paper with a light source category (e.g. transportation, resource extraction) and effect category (e.g. human, wildlife). Additionally, studies were automatically labeled using key words that appeared in the title of the publication (e.g. sleep, bats, turtles, insects).

Number of Studies, 1978-2020

Even though our literature search began in 1978, the first relevant papers were not found until 1991 for wildlife and 1995 for humans. Although some laboratory studies were found before 1991, but not included in Figure 2. For wildlife, there has been an increase in the number of studies published each year beginning in 2011 (Figure 2). For humans, few studies were available before 2011 and no increase in publications per year. In 2016, the first studies on the effects of artificial light at night on plants was published. Review papers are less common for humans, with a few in 2013 and 2015. For wildlife, review papers were the most numerous in 2018.

The number of peer-reviewed studies published each year (1978 - 2020) documenting the effects of artificial light at night based on our WOS search criteria and manual verification. Note: this graphic excludes studies using laboratory animals.
Figure 2. The number of peer-reviewed studies published each year (1978-2018) documenting the effects of artificial light at night based on our WOS search criteria and manual verification.  Note: this graphic excludes studies using laboratory animals. For an alternative way to read this data, see the table at the bottom of this page.

Sources of Artificial Light at Night, 1978-2020

All relevant papers were labeled by a subject matter expert with a category of light source: light from built environment (all sources together), transportation, recreation, resource extraction (which included industrial sources), military, or other. The other category includes studies where light was added in an experimental setting. We did not find any studies where multiple sources were investigated. Most of the human and wildlife studies are focused on light from the built environment.

The two pie charts display proportions of artificial light at night sources for peer reviewed studies on impacts to humans and wildlife from 1978 to 2020. Human studies N = 18; Wildlife studies N = 218.
Figure 3. Proportion of studies within different artificial light at night source categories. Human studies N = 18; Wildlife studies N = 218. These graphics exclude studies using laboratory animals. Data for figure 3 is included in the alternative text below.

Effects on Humans

In the 19 studies on human response to light, 4 studies looked at the effect on sleep, and 3 of the studies looked specifically at the effects of street lighting. One study, a laboratory study of the psychological impact of light pollution in national parks, had direct implications for management of lights in park settings.

Effects on Wildlife

In the 220 studies on wildlife response to artificial light at night there were:

  • 35 on birds
  • 21 on turtles
  • 14 on insects
  • 20 on bats
  • 9 on plants
  • 2 studies in parks or protected areas
An animated word cloud showing the most used words in the abstracts and titles from the studies on the effects of artificial light on wildlife published between 1978-2020. The most common used words changes with each group of years.
A word cloud of most used words in abstracts on wildlife studies, 1978-2020 (220 papers). The largest words correspond to the most common used words: light, alan light, beach light and nesting.

Trends in Topics, 1978 - 2020

To examine different topics discussed in the literature, we generated word clouds for wildlife and human studies from the titles and abstracts for all publications (1978-2020).The animated GIF to the right shows word clouds of topic trends for wildlife publications from 1990-1999, 2000-2009, 2010-2019, and 2020. Early wildlife publications focused on turtle hatchlings, while later studies included more diverse taxa (bats, insects, fish). Human studies were not included in this analysis because of the low number of publications on a decadal scale.

Suggested Reading

A meta-analysis of the impacts of light pollution on animals was published this year (Sanders et al. 2020). Previous studies have been more focused on a specific species, local community, or area. This paper takes an approach that is more ecological and holistic review approach, a more ecological. They classified 126 publications with hundreds of observations from the peer-reviewed literature. The five major response categories were: organismal physiology; seasonal phenology; life history traits; daily activity patterns; and population/community. The authors used these classes to focus on ecosystem function. The results of this article suggest there are significant implications for the mitigation of the effects of ALAN on the natural environment. Another paper of interest was focused on insects. The Grenis and Murphy (2019) paper entitled “Direct and indirect effects of light pollution on the performance of an herbivorous insect” their findings indicate that light pollution can alter plant–insect interactions and may have important community-wide consequences. Impacts on insects is vital for ecosystem function so this paper is a good introduction to the effects of light pollution on insects as is the last suggested reading by Owens et al. (2020). This paper examines light pollution (ALAN) as a driver of insect declines. A stronger recognition of the ways in which ALAN affects insects can help conservationists reduce or eliminate one of the major drivers of insect declines. An important concept is that ALAN is unique among anthropogenic habitat disturbances and anthropogenic pollutants in that it is easy to mitigate and leaves behind no residual effects.

Where to Find More Information

A searchable spreadsheet of all the relevant studies is available upon request (see contact information below) or on our website. The spreadsheet will be updated annually, and an annual briefing document will be prepared and appended to this summary. The results will be shared with the NPS community and archived on our website. In most cases, NSNSD staff has access to the full text of the publications and can share a link, email a pdf, or assist in finding the reference.

Project Contacts

Sharolyn Anderson, PhD; Cathleen Balantic, PhD. Natural Resource Stewardship and Science Directorate, Natural Sounds and Night Skies Division. Email: SoundscapeSupport@nps.gov

2020 Update

The search for publications in 2020 produced 24 papers deemed relevant by a subject matter expert. There were 4 new studies on humans (0 of which were reviews), and 19 new studies on wildlife (2 of which were reviews).In the 19 studies on wildlife response to artificial light at night, there were:

  • 2 on bats
  • 1 on insects
  • 4 on birds
  • 1 on plants
  • 0 on turtles
  • 0 studies in parks or protected areas

The search for publications in 2019 resulted in 84 papers; 51 were found to be relevant by a subject matter expert. 43 new studies on wildlife (1 review); 1 new study on human response (1 review).

In the 43 studies on wildlife response to artificial light at night there were:

  • 10 studies on bats
  • 6 studies on insects
  • 5 studies on birds
  • 3 studies on plants
  • 0 studies on turtles
  • 0 studies in parks or protected areas
A graph that details the number of peer reviewed studies published each year, 2000 - 2020
Figure 4. The number of peer-reviewed studies published each year (2001-2020) documenting the effects of artificial light at night based on our WOS search criteria and manual verification. Note: this graphic excludes studies using laboratory animals. For an alternative way to read this data, see the alternative text at the bottom of this page.

References

  • 1Falchi, F., Cinzano, P., Duriscoe, D., Kyba, C. C., Elvidge, C. D., Baugh, K., … & Furgoni, R. (2016). The new world atlas of artificial night sky brightness. Science advances, 2(6), e1600377.
  • 2Longcore, T., and C. Rich. 2016. Artificial night lighting and protected lands: ecological effects and management approaches. Natural Resource Report NPS/NRSS/NSNS/NRR—2016/1213. National Park Service, Fort Collins, Colorado, 51 pp.
  • 3Seymoure BM, Buxton R, White J, Linares C, Fristrup K, Crooks K, Wittemyer G & Angeloni L. Global light pollution masks natural light cycles and affects numerous species. Under review.
  • 4Cinzano, P., Elvidge C. 2003. Night sky brightness at sites from satellite data. Mem. Soc. Astron. It., 74, 456-457.

Alternative text for Figure 1:

Maps showing the growth in artificial sky brightness due to light pollution in continental United States. The figures contains four panels each with a map displaying artificial night sky brightness on a color scale, from no light (darkest) to pink (brightest). The first panel is shows 1950s, second panel shows 1970s, third panel shows 1997, and fourth panels shows prediction for 2025. The night sky gets progressively brighter through time with the east coast brighter than the west.

Alternative text for Figures 2 and 4:

  • 1991: 1 wildlife study;
  • 1992: 1 wildlife study;
  • 1993: 1 widllife study;
  • 1995: 3 wildlife studies;
  • 1996: 1 human study; 1 wildlife study;
  • 1999: 1 human study; 1 wildlife study;
  • 2002: 2 wildlife studies;
  • 2004: 1 review wildlife study; 1 wildlife study;
  • 2005: 2 wildlife studies;
  • 2006: 3 wildlife studies;
  • 2007: 1 review wildlife study; 2 wildlife studies;
  • 2009: 4 wildlife studies;
  • 2010: 2 wildlife studies
  • 2011: 1 human study; 4 wildlife studies;
  • 2012: 2 human studies; 1 review wildlife study; 4 wildlife studies;
  • 2013: 2 human studies; 1 review human study; 1 review wildlife study; 8 wildlife study;
  • 2014: 1 human study; 1 review wildlife study; 9 wildlife studies;
  • 2015: 1 review human study; 2 review wildlife studies; 17 wildlife studies;
  • 2016: 3 human studies; 2 plant studies; 18 wildlife studies;
  • 2017: 1 human study; 1 plant study; 34 wildlife studies;
  • 2018: 1 human study; 2 plant studies; 3 review wildlife studies; 33 wildlife studies;
  • 2019: 3 plant studies; 1 review human study; 1 review wildlife study; 39 wildlife studies
  • 2020: 1 plant studies; 4 human studies; 0 review-human studies; 2 review-wildlife studes; 19 response studies

Alternative text for Figure 3:

The pie charts display proportions of artificial light at night sources for peer reviewed studies on impacts to humans and wildlife from 1978 to 2020. Human studies N = 18; Wildlife studies N = 218. For human studies, there were 9 studies on light from generic/built sources, 1 on recreation light, 1 on resource extraction light, 3 on transportation light, and 4 on light from other sources. For wildlife studies, there were 112 studies on light from generic/built sources, 6 on recreation light, 5 on resource extraction light, 11 on transportation light, and 84 on light from other sources.

Last updated: November 10, 2021