Artificial Light at Night: State of the Science 2024

by John Barentine
Dark Sky Consulting, LLC

As more people become increasingly aware of light pollution, accessible scientific information is imperative for dark sky advocates, community members, and policymakers to combat this growing environmental threat effectively. However, finding accessible information has always been challenging, especially for those looking for a broad overview of current information regarding artificial light at night (ALAN).

The absence of an accessible and comprehensive overview prompted DarkSky to publish the first “Artificial Light At Night: State of The Science” in 2022, summarizing the scientific understanding of light pollution. Each year, we have continued to update this report.

Before drafting the State of The Science report, DarkSky considers thousands of published papers, theses, and articles, including nearly 5,000 pieces of scientific literature listed in the Artificial Light At Night Research Literature Database. Like assembling a jigsaw puzzle, we identify the most relevant pieces, strategically placing them next to others to create a summary that is understandable and useful.

In a sense, we do the hard work for you, creating a summary that clarifies relationships among topics related to light pollution. This ‘big picture’ approach also helps the dark sky community identify holes in the research or topics that have yet to be investigated.

State of the Science is created with a broad audience in mind, from researchers looking to understand the impact of light pollution on their subjects of expertise to DarkSky advocates in need of concrete evidence to support policy changes at all levels of government. We invite everyone to take a look at this year’s findings to better understand light pollution and the growing environmental threat it has become.

State of the Science 2024
Full Report: https://zenodo.org/records/11431447

2023 was an eventful year for light pollution research. In July, the journal Science for the first time featured light pollution on its cover, precisely 50 years after the first mention in its pages. The special issue featured five comprehensive review papers.

The Royal Society’s Philosophical Transactions B also published a ‘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.”

Clearly light pollution research is coming into its own as a field of scientific investigation.

Several main points emerge from our review of 2023 papers on light pollution. For example:

• Although few studies have broken completely new ground, our conclusions about light pollution have grown stronger. Most studies simply add weight to previous conclusions.
• New remote sensing devices and techniques are giving us unprecedented views of the Earth at night. This provides more granular data about the distribution of ALAN in space and time.
• Understanding how light pollution affects global biodiversity is a top priority. In particular, the role of ALAN in concert with influences like climate change is becoming clear.
• Health researchers sounded the alarm about how ALAN exposure affects older people. In particular, they found evidence for how it interacts with neurodegenerative diseases like dementia and Alzheimer’s.
• The nature of the relationship between ALAN and public safety remains very unsettled. Research into lighting and crime is pivoting. Past research on crime incidence produced ambiguous results. Newer work focuses on users of outdoor spaces and how lighting influences their perceptions of safety.
• Air quality and how it interacts with light pollution was a recurring theme. Some work found more evidence that ALAN alters nighttime air chemistry. This may lead to diminished air quality over cities. In turn, particulate pollution plays an important role in the formation of skyglow.
• Even as concerns rise, the impacts of satellite ‘megaconstellations’ on the night sky are poorly understood. Researchers argue that space companies and government regulators must consider more than the brightness of individual satellites.

These developments mark a clear advance in our knowledge about light pollution. Unfortunately, more questions remain: How does ALAN contribute to species population decline or extinction? To what extent is outdoor ALAN specifically harming human health and well-being? Which light pollution mitigations, especially policy solutions, are most effective? And which kinds of legal mechanisms may be brought to bear on the satellite problem?

While we expect that researchers will wrestle with some of these and many other questions in 2024 and the following years, it remains difficult in most cases to get adequate support for light pollution studies. Being a multidisciplinary subject, most funding agencies don’t know where to place the topic, making total funding of large-scale and complex projects unusual. This often leads to smaller projects, resulting in ‘siloed’ knowledge. However, as the field gains recognition beyond specialized subjects, it becomes more attractive to potential funders.

We end the State of the Science 2024 with a series of questions that we think are most pressing for researchers to answer. We hope that the report will, therefore, benefit researchers, prompting further investigations, as much as we hope it informs researchers outside the world of scientific research.