Synthesis of Studies on the Effects of Artificial Light at Night

1978-2023, with 2023 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. See footnote 4

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 2023. 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 = 535 relevant studies from 1978 to 2023). 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 1978-2023

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 2023.

Figure 2. The number of peer-reviewed studies published each year (1989-2023) 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, 1978-2023

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 = 39; Wildlife studies N = 346. These graphics exclude studies using laboratory animals. Data for figure 3 is included in the alternative text below.

Keyword Trends from 1978 to 2023

In the 39 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 346 studies on wildlife response to artificial light, article titles contained the following keywords:

• 56 on birds
• 24 on turtles
• 26 on insects
• 33 on bats
• 21 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 2020-2023. 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 - 2023

To examine different topics discussed in the literature, we generated word clouds for wildlife studies from the titles and abstracts for all publications (1978-2023).The animated GIF below shows word clouds of topic trends for wildlife publications from 1990-1999, 2000-2009, 2010-2019, and 2020-2023. 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.

2023 Update

The search for publications in 2023 produced 58 papers deemed relevant by a subject matter expert. There were 6 new studies on humans (3 of which were reviews), and 36 new studies on wildlife (6 of which were reviews). (Additional studies were laboratory studies, which are not described in this summary.)In the 36 studies on wildlife response to artificial light at night, article titles contained the following keywords:

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

Figure 4. The number of peer-reviewed studies published each year (2000-2023) 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 human health, plant diversity, and freshwater ecosystems.Wang et al. 2023 conducted a qualitative literature review on ALAN and human health. Through the narrative, they found the biggest impact is on sleep and the indirect effects of lack of sleep. In addition, they concluded with four findings: 1) there needs to be a detailed methodology developed to deal with scale issues of outdoor nighttime lights, 2) additional research is needed on human health consequences and exposure to ALAN both indoor and outdoor, 3) further investigation with a concentration on mental health and behavior is warranted, and lastly 4) the assumption of the causal relationship between ALAN and human health needs to be backed by additional focused research. Wang et al. 2023 also review the positives associated with ALAN, such as feelings of safety which is a perception, and more research needs to be conducted. Others have also pointed out the positives of ALAN, which is by nature human-centric lighting.A new study by Bucher et al. 2023 looked at plant diversity across different lighting regimes. The team set up 12 individual sites in an indoor facility. They established a gradient in ALAN across all 12 from no supplemental light to 30.313 lx in the most light-polluted treatment – an illuminance large as that at pavement level directly underneath a street light. The background illumination within the facility was 1.4 mlx due to interior lighting (ie technical devices). The experiment found that after planting 16 different species in each unit, the productivity decreased with increasing ALAN in the first harvest and little effect for a second harvest. There was no significant effect of ALAN on the plant species richness but the Shannon diversity declined significantly with increasing ALAN. Overall, the study concluded that plant biomass decreased in every unit measured after first harvest. In addition, they found that ALAN negatively affected diversity and some species functional traits. This study informs plant conservation with regard to light pollution.The last article by Holker et al. 2023 examined freshwater ecosystems as an often overlooked area of inquiry. This is a thorough review of the literature on the effects of light pollution on freshwater wildlife and ecosystems. It presents the intensity and spectra that affect freshwater ecosystems in a clear and concise way. The specific lux are given for different species. For example, white light as low as 0.01 and 1 lux can suppress melatonin in some fish species. Remember that a full moon is 0.03 lx at zenith. The conclusion is that we need additional freshwater ecosystem research and that mitigation of both terrestrial and aquatic lighting is needed.

• Bucher, S. F., Uhde, L., Weigelt, A., Cesarz, S., Eisenhauer, N., Gebler, A., Kyba, C., Römermann, C., Shatwell, T. & Hines, J. (2023). Artificial light at night decreases plant diversity and performance in experimental grassland communities. Philosophical Transactions of the Royal Society B, 378(1892), 20220358. https://doi.org/10.1098/rstb.2022.0358 Open Access.
• Hölker F., Jechow A., Schroer S., Tockner K., Gessner M.O. (2023). Light pollution of freshwater ecosystems: principles, ecological impacts and remedies. Phil. Trans. R. Soc. B 378: 20220360. https://doi.org/10.1098/rstb.2022.0360 Open Access.
• Wang, T., Kaida, N., & Kaida, K. (2023). Effects of outdoor artificial light at night on human health and behavior: A literature review. Environmental pollution (Barking, Essex : 1987), 323, 121321. https://doi.org/10.1016/j.envpol.2023.121321

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
• 2023: 1 plant study; 3 human studies; 3 review human studies; 6 review wildlife studies; 30 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 2023. Human studies N = 39; Wildlife studies N = 346. For human studies, there were 21 studies on light from generic/built sources, 2 on recreation light, 2 on resource extraction light, 5 on transportation light, and 8 on light from other sources. For wildlife studies, there were 198 studies on light from generic/built sources, 8 on recreation light, 8 on resource extraction light, 20 on transportation light, and 110 on light from other sources.