Artificial Light at Night: State of the Science 2025

Each year, DarkSky International updates Artificial Light at Night: State of the Science, a comprehensive publication that captures what researchers are discovering about light pollution.

First released in 2022, the report distills findings from thousands of scientific papers, student theses, technical reports, and other sources. The 2025 edition is now available to the public at https://zenodo.org/records/15492393.

DarkSky intends this report to be a trustworthy and reliable summary of the best available knowledge. It is designed to inform and support the work of the advocate community. Users of the report can be confident that its contents are presented in a fair and dispassionate manner, offering an honest assessment of what we do—and don’t—yet know about this important topic.

The report is built on the Artificial Light At Night Research Literature Database (ALANDB), a curated collection of research maintained by scientists working in dark-sky studies. Each year, new papers are added, sorted, and analyzed to identify the most important findings moving the field forward. The result is a synthesis that connects many threads of light pollution research, while also highlighting critical gaps and underexplored questions.

Strong and rising scientific interest

The 2025 update reveals that 2024 was another standout year for ALAN research. We added 547 references to ALANDB, bringing the total number of entries to over 5,000. The chart below illustrates how this number has grown over time.

Over the past decade, the number of papers added to the database has increased steadily at an average rate of about 15% per year—with no signs of slowing down. Simply put, scholarly interest in light pollution is stronger than ever.

The field’s two main conference series—Artificial Light At Night (ALAN) and Light Pollution: Theory, Modeling and Measurement (LPTMM)—continue to break attendance records. During the COVID-19 pandemic, organizers agreed to alternate the events annually, allowing more researchers to attend both. 2024 saw another dynamic edition of LPTMM, with papers collected in a special issue of the Journal of Quantitative Spectroscopy and Radiative Transfer.

A major contribution in 2024 came from Hector Linares and colleagues, who published a high-profile review in Nature Reviews: Earth & Environment on how we measure and monitor light pollution. They concluded that “existing monitoring techniques can only perform a limited number of measurements throughout the night and lack spectral and spatial resolution,” limiting our understanding of how light pollution is evolving globally. They echoed a growing call for dedicated satellite missions to provide better “eyes in the sky.”

Expanding research themes

Several important advances were made last year. Researchers published the first self-consistent model of polarized light in the night sky. New studies highlighted synergies between light pollution and other forms of environmental degradation, such as noise and air pollution. Researchers are also increasingly exploring the social and environmental justice dimensions of ALAN, including how lighting can be used in discriminatory ways.

Ecologically sensitive lighting design saw notable progress in 2024. Evidence continues to grow showing that bespoke lighting designs, tailored to meet ecological needs for nighttime darkness, can dramatically reduce the fatal attraction of species to artificial lights. We now have emerging best practices for specific organisms.

Human health research also made strides. One major study found that nighttime exposure to bright light—and insufficient light during the day—can effectively predict all-cause mortality risk. Another study linked higher levels of indoor light exposure at night to increased systemic inflammation. The body of evidence connecting ALAN to neurological disorders also strengthened, including associations with depression, Alzheimer’s disease, and faster progression of mild cognitive impairment into dementia.

Looking ahead: Open questions and next steps

On the topic of space-based light pollution, more research and commentary than ever is being published. From the value of dark and quiet skies to the social cost of their loss, the conversation is growing. While individual satellites may be getting dimmer, concerns remain about their cumulative impact.

What’s ahead for 2025 and beyond? Many critical questions remain unanswered. For example, do public policies aimed at reducing light pollution actually work? How does ALAN interact with other environmental stressors? We still don’t have definitive answers about how outdoor ALAN affects human health—or even the best ways to study such effects. The relationship between nighttime lighting and crime also remains poorly understood. We lack clear thresholds for “minimum safe” lighting levels, or how much light can be reduced without sacrificing public safety. And we still don’t know how the night sky will change as orbital space becomes increasingly crowded.