Artificial Light At Night: State Of The Science 2024

Image credit: NASA's Goddard Space Flight Center  
1135 words / 5-minute read

Summary: Knowledge is power, but only if it's accessible. The "Artificial Light At Night: State Of The Science" report improves access to the knowledge in thousands of papers about light pollution and its effects. This post explains how the report was written and is updated each year, and it presents some research highlights from 2023.

Accessible scientific information about light pollution and its consequences is key to combating this growing environmental problem. But until recently there were few accessible summaries about artificial light at night (ALAN).

This prompted DarkSky International to publish the first "Artificial Light At Night: State Of The Science" (SOTS) report in 2022. SOTS considers the contents of thousands of published papers, theses and reports. It summarizes the current scientific consensus view on various aspects of ALAN. Written in non-technical language, it includes a comprehensive bibliography to support its content. 

​Each year, DarkSky International updates this report. Such regular updates help keep track of the hundreds of new studies published each year. We are excited to share State Of The Science 2024, which includes the most recent studies and papers published in 2023. 

How SOTS came together

SOTS is in many respects a 'summary of summaries'. The report authors considered almost 5,000 pieces of scientific literature listed in publicly available Artificial Light At Night Research Literature Database, or ‘ALANDB’.

Scientific literature about ALAN is growing quickly. Rising attention to the problem of light pollution has led to a rapid increase in the number of papers published on this topic. The chart below shows the number of papers published each year for the past 20 years that were included in ALANDB. In recent years, the database contents have grown by an average rate of 15 percent per year.

ALANDB contains a variety of kinds of literature, from journal papers to government reports. SOTS prefers peer-reviewed studies as sources. The scientific community holds this kind of material in the highest academic regard. But where appropriate, SOTS includes references to white papers, student theses, and other sources.

Each source added to ALANDB receives one or more of 22 top-level keywords describing the contents of the paper. These keywords help group papers into a set of seven broad categories: the night sky; human health; wildlife and ecology; public safety and crime; energy and climate; and social and environmental justice. In recent years, SOTS included papers about “space light pollution” from swarms of satellites orbiting the Earth. As the database entries are sorted, quality checks weed out sources that have methodology problems . Sources with the most significant results are highlighted for inclusion in the resulting report.

Using ALANDB as source material, the process of composing SOTS is like completing a jigsaw puzzle. Relationships among the topics become clearer as one looks at the 'big picture'. Drawing connections among topics, and sources within a topic, helps reveal underlying trends. We then better understand the state of light pollution science. But we also begin to see where the missing pieces are. Updating the report each year requires only looking at the “new” pieces and seeing where they may fit.

SOTS has several target audiences. One of them is the scientific research community. New researches to this field, in particular, enjoy an accessible introduction. Issue advocates become more knowledgeable about the facts supporting their cause. Policy makers better understand the issues they must decide. And the public finds an entry point to learn about a major social and environmental challenge.

2023 ALAN research developments

2023 was an eventful year for light pollution research. In July, the journal Science for the first timefeatured light pollution on its cover, exactly 50 years afterthe first mention in its pages. The special issue featured five comprehensive review papers. Also, the Royal Society's Philosophical Transactions B publisheda 'themed' issue on ecological light pollution. Its papers "investigate light pollution ecology at various environments and scales, from single processes to whole communities, to better understand the relationship between light pollution, ecological balance, and human influence."

​​The 504 ALANDB sources published in 2023 that were considered for SOTS report break down by major keyword as shown in the pie chart below.

Fully 75% of the papers are about wildlife, remote sensing (of ALAN), or human health. They have been the leading topics for the past few years.

Certain key points emerge from the survey of papers published in 2023:

• Few studies break completely new ground, but scientific conclusions about light pollution grew stronger. Most studies simply add weight to previous conclusions.
• New remote sensing tools and techniques give unprecedented views of the Earth at night. This provides more granular data about the distribution of ALAN on land and through time.
• Understanding how light pollution affects global biodiversity is a top priority. In particular, the role of ALAN as it interacts with influences like climate change is becoming clear.
• Health researchers sounded the alarm about ways in which ALAN exposure affects older people. In particular, they found connections to neurodegenerative diseases like dementia and Alzheimer's.
• The nature of the relationship between ALAN and crime remains very unsettled. Past research on ALAN and crime incidence yielded ambiguous results. But newer work focuses on users of outdoor spaces and how lighting influences their perceptions of safety.
• Interest in how light pollution may influence air quality is rising. Some studies found further evidence that ALAN alters the nighttime chemistry of air, linking to poor air quality over cities. In turn, certain kinds of air pollution affect the formation of skyglow.
• The impacts of satellite 'megaconstellations' on the night sky are still poorly understood. Researchers now look at factors beyond only the brightness of individual satellites.

Prospects for 2024 and beyond

Recent research achievements mark a clear advance in our knowledge about light pollution. But many questions remain. SOTS concludes with a list of some of these questions, such as:

• How does ALAN contribute to species population decline or extinction?
• To what extent is outdoor ALAN harming human health and wellbeing?
• Of known light pollution mitigations, especially policy solutions, which are most effective?
• Which kinds of legal mechanisms may help solve the satellite problem?

We expect that researchers will wrestle with these and many other questions in 2024 and beyond. New kinds of light-sensing devices are becoming available, as well as new platforms on which to place them. Computer models of skyglow grow more sophisticated and their outputs more realistic. Possibilities for engaging citizen scientists in research abound. And a new generation of young scientists is enriching the field.

Yet it remains difficult in most cases to get adequate support for light pollution studies. It's a multidisciplinary subject, and many funding agencies don't know where to place it. Full funding of large-scale, complex projects is still unusual. This often leads to 'siloed' knowledge that may hold major advances back. But as the field gains mainstream recognition, it becomes more attractive to potential funders. Expect new breakthroughs as access to resources improves.

Want to learn more about the SOTS 2024 report? Have a look at this presentation from our own John Barentine to the DarkSky International advocate community introducing the report and reviewing its highlights: