​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?

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.

​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.

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.

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?"

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.

​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.

Our world is one of generally complicated problems that lack simple solutions. Reality is often messy and confusing. Yet politics gravitates toward easy fixes and even promises them. Ill-conceived attempts to solve such problems can make things worse by generating new ones.

Such is the case where the interaction of outdoor lighting and crime are concerned. We have written here in the past about that interaction. We pointed out how inconsistent the data are. And we explained why "feelings of safety" may have more to do with lighting and crime than any other underlying relationship.

New research by Paul Marchant and Paul Norman published in Applied Spatial Analysis and Policy challenges the narrative again. They challenge the underpinnings of much of the scholarly literature on the subject. They also show in a well-researched case study how 'common sense' assumptions about lighting and crime may be flat wrong. This post is as much about how scientists do research as it is about the result of the specific study used as an example.

Marchant and Norman examined data from the city of Leeds, UK, during a massive municipal street lighting retrofit. Between 2005 and 2013, Leeds replaced some 80,000 street lights over its administrative territory. The city exchanged its old sodium-vapor lighting for ceramic metal halide luminaires.

First, in 2022 the pair looked into whether changing to white light street lamps improved road safety. They found "no convincing evidence ... for an improvement (or detriment) in road safety by relighting with white lamps, despite the extensive, city-wide installation efforts and associated costs." In other words, there was no evident effect one way or another. The study did not find evidence that the new lighting had affected traffic safety despite there being over 19,000 road traffic collisions in the data set.
To secure UK Private Finance Initiative funding for the retrofit, the city touted expected benefits due to crime reduction. A key claim involved a 20% reduction in night-time crime. This, in turn, would lower social and economic opportunity costs associated with crime. And it would yield a Benefit to Cost Ratio (BCR) of 3.75 — an impressive return on investment. The retrofit cost was borne at least in part by this forecast.

The Leeds case is one of the largest-scale municipal lighting retrofits studied rigorously to date. But the results show that its influence on crime was close to zero. "The upshot of all the fitted models," the authors wrote, "is that the effect of the new replacement white lamps on crime is small."

We recently interviewed lead author Paul Marchant for more on his paper and its significance. His illuminating (!) answers below are lightly edited only for length and clarity only.


​DSC: Can you briefly summarize the method used in your paper for a lay audience?

​Marchant: The study analysed the weekly counts of crimes that were recorded by the police in each of the 107 geographical areas comprising the whole of the UK city of Leeds, as streetlighting was changed from orange to white light, over a period of nearly 9 years. The method uses the fact that the replacement new white lighting is introduced into each of the 107 areas in different amounts at different times.

Therefore, each area is at a different stage of completion at any given time and so it is possible to assess what these differences in lighting between areas lead to in terms of differences in the occurrence of crime.

Different areas suffer different amounts of crime, with some experiencing a lot whilst others only a little. The multilevel analysis treats the 107 series as a ‘family’, so that the overall levels of crime can be modelled as coming from a statistical distribution with a certain average weekly crime rate and a certain spread in rates. Similarly other distributions are formed for aspects of the underlying area-specific trends that are either increasing or decreasing the amount of crime, due to causes other than the nature of the streetlighting.

Crucially the modelling involved a term for the amount of new lighting each area had received at a given time point. This allows the effect of the new lighting to be separated from the underlying trends in crime in the different areas. Therefore, the effect on crime of the full complement of new lamps can be determined.


DSC: At the same time it was important to you to show why earlier reports in the literature are often unreliable. You point to several factors, from 'untrustworthy controls' to unavailability of the source data. Do you think something nefarious is going on with respect to lighting and crime studies? Does it have something to do with who funds the research?

Marchant: Frankly I don’t know, but it certainly needs to be guarded against. Transparency and openness are paramount for good science. There are concerns about such as conflict of interest bias even in the regulated clinical trials area, as outlined in the Cochrane Collaboration Handbook. Anyone interested in issues around the matter of lighting and public safety, and associated concerns of poor quality research, might like to read my article ‘Investigating whether a crime reduction measure works’. It explains how and why I started pursuing the issue.


DSC: Given the many effects that complicate light/crime studies, one might assume that getting at underlying relationships is nearly impossible. Do you think anything like a dose-response relationship between light and crime will ever be demonstrated? Or is human behavior just too complex for that?

Marchant: In principle it could be possible, as even very small effects can be found and estimated with enough of the right sort of data, sensible modelling and enough computing power to analyse it. Personally, I wonder whether some crime researchers talk of “dose-response” so as to (wrongly) give the impression that their work is just like that of a clinical trial. In a comprehensive study of lighting, one ought also take account of the characteristics of the places in which the different lighting is installed, to make its results more generalisable. One can conceive of a very elaborate study even involving randomisation but such would take a lot of resources!


DSC: The shortcomings of research study design can lead to poor-quality flooding the literature. How much research of a doubtful nature do you think is out there that never gets scrutinized (yet eventually becomes part of the folklore)?

Marchant: In this field, my answer is most of it! Indeed, researchers seem to have never heard of regression towards the mean. They wrongly assume the counts are Poisson [distributed] and this assumption can’t be checked as they only use ‘before and after studies’. I suspect that they may have only done basic statistics courses in which it is only statistically independent events that are analysed.

I believe ‘folklore' is an appropriate term as bad practice is just passed on with no adequate questioning of whether, for example, the method is appropriate or that the assumptions underpinning the method are met. The problem is that it is very easy to put some data into a computer, press the button for an unwittingly inappropriate analysis, get some other numbers out and call that the result. Reviewers of journal articles are also likely to have also been inculcated into the same folklore of the field.


DSC: The conventional wisdom about research is that one way to avoid at least some of these problems is to 'pre-register' study protocols. In this framework, scientists state their intended data collection, reduction and analysis procedures up front. Not only that, but they are further encouraged to publish these plans. This helps keep researchers honest, because any attempts to fit data to models after the fact will be more conspicuous. Yet comparatively few studies do this. Why do you think researchers avoid pre-registering their methodologies?

Marchant: Registration wasn’t always the case for clinical trials and it has taken a while for the practise to diffuse into other areas of inquiry. The ‘replication crisis’ has been a source of great concern about poor research. I think there has been progress in experimental areas in which a planned intervention is made, but registration is less common in observational studies, which just collect observations, when there is no planned / organised intervention. However, things are gradually changing and some organisations, like the Center for Open Science, are encouraging and facilitating the practice. Some journals like PLOS ONE also publish plans for research, which also allows comments like this to be made. The protocol for our study was not publicly registered but was sent to three competent [and] suitably qualified academics.

I am somewhat surprised in these cost-conscious times, that if a policy has been introduced on the basis of alleged evidence more checks are not made that the policy has achieved what it was intended to. I think that a big part of the problem is that the political class tends to be rather poor at statistical thinking.


DSC: What do you think would make for a good way forward in this field of research?

Marchant: To apply this multilevel method to datasets from other places, involving lighting changes, where there is appropriate data for ‘outcome measures’, such as crime or road traffic collisions. [And] get more statisticians involved. Many researchers use statistical analysis but this does not make them statisticians. Try to engage those who ideally have a higher degree in the discipline of statistics, are recognised by a professional body, such as the American Statistical Association and who undergo continuous professional development in the subject. Try to engage statistical epidemiologists as there are parallels between disease and crime in society.


DSC: Is the Leeds example a sufficiently cautionary tale that officials in other cities might think twice before acting more on instinct rather than evidence?

Marchant: Yes! Also, a good rule of thumb is not to believe that a salesperson is giving entirely unbiased information. It would be a step forward if policies were implemented in ways that would make an evaluation straight-forward and that post implementation performance is routinely checked by those who are statistically well-qualified and independent.


DSC: If your work offered one important takeaway message for readers, what would it be?

Marchant: Just because it’s a commonly held belief that lighting beats crime doesn’t mean that the claim shouldn’t be checked out. The recent Marchant and Norman study, which counters some of the shortcomings of other studies on the subject, suggests that any effect of changing to brighter white lighting, either detrimental or beneficial, was at most rather small, and not at all what was expected. There seems to be no reason to expect that the effect of such relighting would be any different elsewhere and so the anticipation of crime reduction is not a sound reason for increasing lighting.


​As we wait to find out where lighting and crime research is going next, this new work offers some appetizing food for thought. We thank Paul Marchant for sharing his insight with our readers.

Summary: A diverse group of the world's light pollution experts recently met at the Artificial Light At Night 2023 conference. The main themes of the conference and important results presented there are reviewed, giving a sense of the research community's current direction.

Many of the world's experts on light pollution recently met in Calgary, Canada, to discuss their latest findings. The Eighth International Conference on Artificial Light At Night (ALAN) was held in Calgary, Canada during 11-13 August 2023. We were there to learn about recent research results and new directions that ALAN science is heading.

The ALAN conference series began in 2013. Starting with the 2018 edition, it occurs every other year, alternating with the Light Pollution: Theory, Modeling and Measurement conference. This year's edition saw its highest level of participation from the largest number of countries ever. 108 people attended in person on the University of Calgary campus and about 50 participated as virtual delegates. 

This year’s attendees represented every populated continent except Africa. The participants represented some 28 countries. One-third of attendees were students, many of whom study ALAN as part of their graduate thesis or dissertation work. Despite some computer networking issues, virtual participation in the conference seemed strong. Besides to the in-person event in Calgary, a virtual poster session took place in late July using the Gather.town environment online.

The ALAN Steering Committee accepted so many of the submitted abstracts that much of the in-person event ran in two parallel sessions. The broad topical content of the tracks was ALAN impacts on wildlife and ecology, and measurements and monitoring of light pollution. These tracks reflect where the majority of the research interest (and funding) are at this point in the field's history. There were fewer presentations about social science and public policy than in past years.

Land acknowledgements were a frequent part of the proceedings. Former Calgary city councilor Brian Pincott explained that this is part of the ongoing truth and reconciliation process in Canada. "We have a lot to do to make sure our future includes everyone," Pincott said during his conference wrap-up on Sunday afternoon.

Jennifer Howse (University of Calgary) gave the banquet talk, "Reclamation Under Alberta Skies", on Saturday night. Howse, a Métis woman, used her time to bridge the worlds of her Indigenous and European ancestry with the modern world in the context of her dark-sky work.  She noted the importance in many Indigenous cultures of asking the question “How will people in seven generations live?” Howse also advised listeners to ponder that question in light of our activities that impact space and the night sky.

It reminded attendees that the next frontier of dark-sky conservation involves social and environmental justice concerns. Diane Turnshek (Carnegie Mellon University) raised the issue of the increasing number of people who have never seen the Milky Way. It is therefore challenging to communicate with them about starry skies when this is not something they have directly experienced.  Waleska Valle (Adler Planetarium) spoke about her experience working with youth in Chicago to identify the ways in which light pollution impacts their communities. And Doug Sam (University of Oregon) used the International Dark Sky Park designation effort at Mesa Verde National Park as a case study to examine such efforts through the theoretical framework of decolonization. “When we designate future IDSPs, we must involve native peoples as a matter of justice," Sam explained. 

As usual, the scientific presentations were all high-quality and stimulated lively discussion. The main takeaways from the posters and talks include:
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• The research community needs standardized protocols for measuring ALAN and reporting data, but we seem no closer to deciding on what those are.
• Our measurement devices are still far from perfect and some show signs of aging in the field.
• Yet as devices and software improve, we are learning more about the detailed distribution of ALAN in 3-D, particularly in urban contexts.
• Understanding how animals behave due to a given lighting environment is of foundational importance to ecological studies of ALAN.
• At the same time, the evidence for ecological harms associated with ALAN exposure continues to mount.
• The next frontier of dark-sky conservation practice involves social and environmental justice concerns.
• As the global population ages, we need to rethink why and how we light our world and so do in a way that is inclusive of the amount of “visual diversity” that now exists.
• Further engagement with those exploring ALAN issues from perspectives from the humanities would benefit the research community.

​Friday night saw a successful public outreach event put on by the ALAN conference in coordination with the Royal Astronomical Society of Canada Calgary Centre. About 300 people attended the event, which included an introductory talk about light pollution and a panel discussion with researchers. Afterward, attendees could view the night sky through telescopes set up on the University of Calgary campus.

As participants began to disperse and head home beginning on Sunday, many reported how refreshing the experience was. ALAN 2013 was the first in-person conference in the series since 2018. The  onset of the COVID-19 pandemic in 2020 caused the organizers to pivot to an online-only format.

For many, the Calgary conference was the first time they saw their colleagues in person since 2019. Given that the research community is still small, the ALAN conferences feel more like village assemblies. A return to meaningful, in-person interactions supports the kind of collegiality that constantly draws students who want to make a career of night studies. It also supports collaborations that become friendships while yielding high-quality research results that push the field ahead. 

It is traditional to name the next host city at the conclusion of ALAN. On Sunday, attendees learned that the next meeting will be held in County Mayo, Republic of Ireland, in October 2025. Already many look forward to their next opportunity to present their work, reunite with old friends and meet new ones.