Conference report: Artificial Light At Night 2025

Image credit: ALAN Steering Committee
1588 words / 6-minute read

​At the end of October we traveled to Westport, Ireland, for the Ninth International Conference on Artificial Light at Night ("ALAN 2025"). This biennial event brings together scientists, lighting experts, environmentalists, and community leaders to hear the latest in both research and practice relating to outdoor lighting and light pollution. This edition of the meeting series saw attendees from 42 countries on six continents, making it the most internationally diverse ALAN conference yet. The focus of the event was simple but powerful: How does artificial light at night affect our world, and what can we do about it?

The big picture: Light at night is pollution

A major shift in thinking became very clear this year. Many experts now agree that all artificial light at night counts as a form of environmental pollution. This doesn’t mean that we must cut all nighttime light emissions. Rather, the emerging sense is that we should treat nighttime light with the same consideration we apply to other forms of pollution. We should use it only when needed and then in the most responsible way possible. And although the field hasn’t settled on a single definition of “light pollution,” most people at the conference argued that we already know enough to start taking action. What’s missing isn’t information, but rather political will.

Dara Calleary, Irish Minister for Rural and Community Development and the Gaeltacht Minister for Social Protection, opens the proceedings on the first day of ALAN 2025.

A growing, but not yet global, movement

​One of the most exciting moments at ALAN 2025 was the official launch of the European Light Pollution Coalition, a new alliance working to protect natural darkness across Europe. Its creation may signal a shift toward a more globally balanced movement less dependent on its traditional centers. But the conference also revealed gaps. For example, no researchers from China attended, despite the country’s sizable influence on research. So while the movement is growing, there’s still work to do to make it truly international.

Highlights From ALAN 2025

How we measure nighttime light is changing

Researchers are getting better at understanding what the night actually looks like. A few standout developments:
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• New computer models are making it possible to simulate how light spreads through the atmosphere with much greater accuracy.
• Elena Maggi (University of Pisa) described development of a fully submersible underwater camera system to be used to characterize the ambient light field at night.
• Understanding the significance of measurements continues to evolve. Maggi also noted that "measuring [in general] is not ‘measuring’" to an ecologist. Researchers must define different measurement regimes depending on the relevant ecological context.
• Experts say the most useful measurements now include both color and direction, not just intensity. That's true even as single-channel/panchromatic devices like the Sky Quality Meter remain the de facto workhorse instrument for measuring night sky brightness.

Prof. Zoltán Kolláth (Eszterházy Károly Catholic University and Konkoly Observatory, Hungary) presents work recently published in the Journal of Quantitative Spectroscopy and Radiative Transfer.

Satellite remote sensing: Great potential and big limitations

Satellites are essential for tracking how bright Earth has become at night. But some widely used platforms are missing key information. The most common satellite sensor used in studies can’t detect many modern LEDs because it isn’t sensitive to color. Alejandro Sánchez de Miguel (Instituto de Astrofísica de Andalucía, Spain) noted that lighting "trends based on DNB images are wrong", referring to the NOAA Visible Infrared Imaging Radiometer Suite Day-Night Band instrument. Satellite sensors like the DNB that are not color sensitive simply do not detect all light emissions from certain sources.

Better satellites now exist. An example is the Chinese SDGSAT-1 mission used to create a new European map of nighttime lighting that includes color. Conference attendees heard that researchers are pushing for a dedicated European “night lights” satellite. Yet even a successful mission proposal means it won't launch until at least 2036. Some presenters also warned that valuable U.S. satellite data could be at risk if long-term funding and storage aren’t secured.

Wildlife and ecosystems: Light pollution is a bigger deal than we thought

Light pollution is increasingly defined as one among many important human-made influences. Researchers argue that it should be part of a multi-stressor approach. Elena Maggi presented this as a “more-than-the-sum-of-the-parts result.” There’s growing interest in:

• Understanding how ALAN harms “ecosystem services” (the benefits nature provides to humans);
• Calculating the economic cost of losing those services;
• Deciding which species to focus with limited resources for conservation; and
• Finding better ways to measure how light affects animals—not just humans.

On that last point, a new "biological V(λ)" is in development intended to better quantify lighting impacts on non-human biology. This is a representation of the sensitivity of different organisms to light according to its color.

Lighting design should start with darkness

Lighting professionals at the conference shared a clear message: good design begins with darkness, not light. Chiara Carucci (Noctua) related that the idea is to treat light like a tool, not an end it itself. It should involve only what’s absolutely necessary. Designers should choose lighting that’s gentle on wildlife, human sleep, and the night sky.

Several speakers argued that industry has the technology to do this, but not always the understanding of why it matters. Andy Jechow (Brandenburg University of Applied Sciences, Germany) noted that while industry often has the engineering knowledge to make what we want, it sometimes “doesn't understand the ‘how’ and ‘why’.” For example, at times it struggles with the idea of controlling light with optics rather than added external shielding.
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There is strong interest in standardizing a set of metrics and measurement protocols in light pollution research. Jechow advocated for the ‘utilance’ of lighting (what fraction of light emissions reach the intended target). Julieta Cignaccio, an Aalborg University PhD student, suggested that because visual perception originates in luminance, a luminance-based metric would be most appropriate. And Brian Espey (Trinity College Dublin, Ireland) called for a more general metric characterizing light pollution in the broadest sense: "Is light pollution getting better? Worse? Bigger? Smaller?"

Conference attendees on a nighttime lighting walk around the city center of Newport, Ireland.

Policy: Turning knowledge into action

Policy experts emphasized that we have many untapped opportunities to reduce light pollution. For example, biodiversity laws may can regulate lighting, even when they weren’t written with lighting in mind. Yana Yakushina (University of Ghent, Belgium) suggeted looking beyond traditional policy tools to create “coherent legal frameworks”. This includes leveraging environmental policies that may not seem on the surface to address light pollution.

In some places, like Ireland’s County Mayo, more than a quarter of all nighttime light comes from public streetlights alone. As Laura Dixon (Mayo County Council staff) pointed out, that meaning governments have an outsized influence. But when working with decision makers, nothing beats showing them good and bad lighting in person. Stijn Vanderheiden (Flemish Government) argued from his experience working with decision makers that they need to see good and bad outdoor lighting in context. They can then receive relevant information in a concise and useful way.

New mapping tools are helping communities see both exactly where dark places still exist and how to protect them. Vanderheiden gave as an example the new Belgian Astronomical Darkness Necessity Map. Its purpose is to "identify and map scientific, educational, cultural, recreational locations." The creators plan to make a template version available for others to use.

Several speakers noted that most policymakers aren’t opposed to change; rather, they don’t know how light affects the environment. But, as Vanderheiden pointed out, policy makers must start changes. That is, public pressure alone isn't enough.

Human health: It's not just about blue light at night

You’ve probably heard that blue light at night is bad for sleep. That’s true, but it’s only part of the story. At ALAN 2025, researchers explained that even yellow or orange lights can disrupt our body clocks if they’re bright enough. Rob Lucas (University of Manchester, UK) recounted the development of the newer metric called Melanopic Equivalent Daylight Illuminance (“melanopic EDI”). It does a much better job of describing how lighting affects our circadian rhythms. It's important to “avoid lights that 'look' blue,” Lucas advised attendees. Failing to take into account spectrum can under/overestimate effective ‘doses’ of light. In turn, this may imply false equivalence and fuel inappropriate lighting design.

Culture and community: Rethinking our relationship with the night

Social scientists reminded attendees that while the night is always part of nature, we tend to forget that in our over-lit cities. Nick Dunn (University of Lancaster, UK) argued that darkness has become "provisional" in cities, where we don’t often think of why exactly we use light. Nona Schulte-Römer (Humboldt University, Germany) encouraged communities to think more deeply about why we use light in cities and recognize that different groups of people experience nighttime lighting very differently. She underscored the idea that "There is no one ‘public.’ There may be many." Practitioners and activists should thus avoid approaching engagement as though the public were a monolithic entity.
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Effective change comes from focusing on people first and not just policies. Mike Hawtin (North York Moors National Park, UK) summed it up: “We don’t have 'policies.' This is absolutely about people.” He described "engagement at scale" in his park from the smallest parish councils to largest private landowners.

Looking Ahead: ALAN 2027 in Chile

​The next meeting will take place in Valparaíso, Chile, in July 2027, an important step toward ALAN a truly global conversation. Leading the local organizing committee for the 2027 event, Prof. Sebastian Fingerhuth (Pontifical Catholic University of Valparaíso) welcomed all in attendance to visit his country and and enjoy what promises to be another productive and valuable event.