Synthesis of Studies on the Effects of Artificial Light at Night

1978-2022, with 2022 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 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 patterns 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 guarantee 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.

Figure 1. Simulation of light pollution growth in the United States.

Finding Relevant Studies

In 2018, we established 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.Since then, we have conducted yearly literature searches following the same protocol, up to and including 2022. 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 = 477 relevant studies from 1978 to 2022). Papers that were not relevant included those that just 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, 1978-2022

Even though our literature search began in 1978, the first relevant papers were not found until 1991 for wildlife and 1995 for humans. 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 were published. For wildlife, review papers were the most numerous in 2021.

Figure 2. The number of peer-reviewed studies published each year (1978-2022) 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, 1978-2021

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.

Figure 3. Proportion of studies within different artificial light at night source categories. Human studies N = 23; Wildlife studies N = 275. These graphics exclude studies using laboratory animals. Data for figure 3 is included in the alternative text below.

Keyword Trends from 1978 to 2022

In the 33 studies on human response to light, 8 studies looked at the effect on sleep, and 5 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 (Benfield et al. 2018), had direct implications for management of lights in park settings.In the 310 studies on wildlife response to artificial light, there were:

• 50 on birds
• 22 on turtles
• 25 on insects
• 29 on bats
• 20 on plants
• 3 studies in parks or protected areas

The animated GIF shows word clouds of topic trends for wildlife publications from 1990-1999, 2000-2009, 2010-2019, and 2020-2022. Early wildlife publications focused on turtle hatchlings, while later studies included more diverse taxa (e.g., bats, insects, fish). Human studies not included.

Trends in Topics, 1978 - 2022

To examine different topics discussed in the literature, we generated word clouds for wildlife studies from the titles and abstracts for all publications (1978-2022).The animated GIF below shows word clouds of topic trends for wildlife publications from 1990-1999, 2000-2009, 2010-2019, and 2020-2022. Early wildlife publications focused on turtle hatchlings, while later studies included more diverse taxa (e.g., bats, insects, fish). Human studies were not included in this analysis because of the low number of publications on a decadal scale.

2022 Update

The search for publications in 2022 produced 69 papers deemed relevant by a subject matter expert. There were 10 new studies on humans (2 of which were reviews), and 31 new studies on wildlife (3 of which were reviews). (Additional studies were laboratory studies, which are not described in this summary.)In the 31 studies on wildlife response to artificial light at night, there were:

• 3 on bats
• 4 on insects
• 3 on birds
• 5 on plants
• 1 on turtles
• 1 studies in parks or protected areas

Figure 4. The number of peer-reviewed studies published each year (2001-2022) 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.

Suggested Reading

This year’s suggested articles address ALAN impacts on urban areas, marine ecosystems, and plant productivity. Katabaro et al. (2022) reviewed the impact of light pollution in urban areas. They found that nocturnal species were susceptible even to weak and temporary lighting (in addition to high-intensity urban lighting). In plants, artificial lighting prolongs day length, which has downstream impacts on the entire ecosystem. ALAN also can encourage growth out of season, affect leaf on/leaf off timing, and impact plant ability to synchronize with environmental changes. Not all ALAN impacts were negative, however; the review showed that nighttime artificial light had nuanced effects on urban ecosystems and green spaces (for example, ALAN may hurt ecosystem function, but positively impact green spaces that have high plant density and a lack of natural light). Marangoni et al. (2022) examined the impacts of ALAN in marine ecosystems, filling a necessary gap in a research field that has largely focused on terrestrial effects The article reviewed 202 papers. The authors summarized ALAN effects on marine biota, seashores/coastal areas, sea turtles, intertidal zones, shallow coral reef ecosystems, and vertical aspects of oceans. This work includes a separate section on seabirds due to the mobility of the species. There were ALAN impacts to all reviewed topics, with some species and/or ecosystems more influenced by ALAN than others. The paper also discusses where additional research is needed. Lastly, the review incorporates an inclusive management strategy that presents mitigation support, conservation guidelines, and strategies for protecting dark sky environments.Finally, Liu et al. (2022) examined how ALAN affected the performance of common and rare alien and native plant species in Germany. The authors examined both direct impacts and indirect impacts (via flying insects). The study found that common plants produced more biomass than rare ones under ALAN conditions. This might lead to competitive exclusion of rare species, which could have further cascading impacts. Additionally, the alien plants benefitted more from ALAN than the native plants, potentially suggesting that ALAN increases the risk of invasive plants.

• Katabaro J.M., Yan Y., Hu T., Yu Q., & Cheng X .(2022). A review of the effects of artificial light at night in urban areas on the ecosystem level and the remedial measures. Front. Public Health 10:969945. doi: 10.3389/fpubh.2022.96994. Open Access.
• Liu, Y., Speißer, B., Knop, E., & van Kleunen, M. (2022). The Matthew effect: Common species become more common and rare ones become more rare in response to artificial light at night. Global Change Biology, 28, 3674– 3682. https://doi.org/10.1111/gcb.16126. Open Access.
• Marangoni, L. F. B., Davies, T., Smyth, T., Rodríguez, A., Hamann, M., Duarte, C., Pendoley, K., Berge, J., Maggi, E., & Levy, O. (2022). Impacts of artificial light at night in marine ecosystems—A review. Global Change Biology, 28, 5346– 5367. https://doi.org/10.1111/gcb.16264. Open Access.

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.

For a summary of past suggested reading, please click here.

Project Contacts

Sharolyn Anderson, PhD; Cathleen Balantic, PhD. Natural Resource Stewardship and Science Directorate, Natural Sounds and Night Skies Division. Email: [e-mail]

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 figure 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 shows 1950s, second panel shows 1970s, third panel shows 1997, and fourth panel 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 & 5:

• 1991: 1 wildlife study;
• 1992: 1 wildlife study;
• 1993: 1 wildlife 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 study; 4 human studies; 0 review-human studies; 2 review-wildlife studies; 19 wildlife response studies;
• 2021: 6 plant studies; 4 human studies; 0 review human studies; 2 review wildlife studies; 55 wildlife response studies
• 2022: 5 plant studies; 8 human studies; 2 review human studies; 3 review wildlife studies; 28 wildlife 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 2022. Human studies N = 33; Wildlife studies N = 310. For human studies, there were 16 studies on light from generic/built sources, 2 on recreation light, 2 on resource extraction light, 5 on transportation light, and 7 on light from other sources. For wildlife studies, there were 173 studies on light from generic/built sources, 8 on recreation light, 8 on resource extraction light, 19 on transportation light, and 100 on light from other sources.