Light pollution is now pervasive in our world. Experts and governments more often recognize it as a form of environmental pollution. The tide of public awareness continues to rise. Both light pollution and dark skies are topics of media stories, television shows and podcast episodes. One finds in them clear messages: artificial light at night (ALAN) threatens the natural world.

Yet stories and presentations tend to consider the matter at only a shallow depth. Detailed 'deep dives' are few. It can be difficult to understand the topic very well by only consuming those media. At the same time, access to accurate and reliable information is more important than ever. And both decision makers and the public need that information now more than ever.

This month we look at the latest global view of light pollution and ALAN science. We highlight some key research findings published in 2025 and consider the most important unanswered questions. 

In 2022 DarkSky International released the first report called "Artificial Light at Night: State of the Science". It aimed to present the best of what we know about light pollution in a way that the public can understand. It surveyed a landscape of almost 4,000 published papers and studies in the ALAN Research Literature Database.

The text distilled decades of scientific research into a few pages of understandable language. Hundreds of source citations supported its conclusions. The organization published the report under a Creative Commons license to enable its re-use.

Each year DarkSky International updates the report with the latest results from scientific studies of ALAN. It culls through over 500 new papers published on average each year. In these sources it looks for the common threads tying new results to a growing body of knowledge. The search sometimes turns up unexpected results worth highlighting. It also updates existing knowledge with new source citations.
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The annual update ensures that DarkSky International and its dark-sky advocates stay current on new scientific developments. The report is a valuable resource for the advocates in communicating with both the public and policy makers around the world. It also adds credibility to their advocacy.

The report for 2026, released last month, finds light pollution a bigger social and environmental concern than ever. Studies published in 2025 both build on previous knowledge and reveal some surprises. Here we highlight some notable examples.

Our understanding how ALAN lights up the night sky is now very sophisticated. Miro Kocifaj (Slovak Academy of Sciences and Comenius University, Slovakia) and co-workers published the first model of night sky brightness that accounts for various cloud types and coverage. Their model "can be used to explain observational data collected by light pollution monitoring networks, particularly at sites where the combination of amplifying and darkening effects of clouds generates ambiguous brightness outcomes."

Light pollution has distinct synergies with other pollutants. Yongbin Wang (Xinxiang Medical University, China) led a team that explored links between ALAN and air pollution. They found that the combined effects elevated the risks of high blood pressure, heart and liver disease. They conclude that "policy interventions targeting light pollution reduction and air quality improvement are urgently needed to mitigate environmental health risks."

ALAN is causing ecological changes with profound effects, especially in cities. Lvlv Wang (Wuhan University, China) and coauthors examined the competing effects of light pollution and urban heating on plants. Plants exposed to ALAN experienced a longer growing season compared to those affected only by warm nighttime temperatures. They argued that "ALAN is a critical driver of vegetation dynamics in cities, one we should consider during urban management and development."

ALAN may affect entire ecosystems. It was long believed that light pollution had local-to-regional effects on segments of natural systems. But a Nature Climate Change paper by Alice Johnston, Jiyoung Kim and Jim Harris (Cranfield University, UK) found something very different. ALAN seems to influence the cycle that governs the exchange of carbon between the living and non-biological worlds. This has serious implications for a planet that continues to rapidly warm.

Public acceptance of outdoor lighting policies finds its roots in perceptions of darkness. Two papers provided new social science data assessing the public's attitudes toward nighttime darkness. Richard Jedon (Eindhoven University of Technology, Netherlands) and colleagues showed that increased anxiety experienced by pedestrians in dark areas of cities "made participants less willing to allow lower levels of streetlighting".

Meanwhile, Solène Guenat and Nicole Bauer (Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Switzerland) demonstrated that study participants "who lived or grew up in high-sky brightness regions were more likely to feel unsafe". They also have a more favorable view of ALAN as having social benefits, decreasing its recognition as a pollutant.

Space light pollution continues to rise. As the orbital space around the Earth fills with tens of thousands of new satellites, researchers expect the night sky to get brighter. Rockets and satellites shedding debris in space are especially concerning. In a study of low-Earth orbit space, Miro Kocifaj , František Kundracik and Stefan Wallner reported projections "an increase in night sky background brightness of 5 to 11 per cent above natural levels" by 2035. In some parts of the world, this increase could exceed the amount of ground-based light pollution.

"Artificial Light at Night: State of the Science 2026" closes with a summary of the most pressing research questions of our time. New additions this year include:

• Which lighting policy interventions are most effective in reducing skyglow? Are lighting policies effective? If not, why?
• Are organisms evolving responses to light pollution?
• Can any reliable ‘dose-response’ relationship be defined between outdoor ALAN and safety and/or security?
• How are some measures of ALAN such as skyglow specifically related to a suite of undesired outcomes (e.g., adverse ecological, health, or astronomical outcomes)?
• Is it possible to define an overall efficiency metric for outdoor lighting that considers both its energy efficiency and unintended, negative environmental/social consequences?
• How will novel uses of outer space, such as the deployment of orbital sunlight reflectors, change nighttime conditions on Earth?

The expanding body of artificial light at night (ALAN) research published in 2025 represents a turning point. Our understanding of the profound ecological, physiological, and cultural impacts of light pollution is deepening. We recognize that the gap between scientific consensus and public policy must close.

The task of science now is to address the remaining unanswered questions. Its findings can help translate data into actionable local, national and international protections. In turn, we can begin to reverse the tide of global skyglow and safeguard the nocturnal commons for generations to come.

For as much as we know about light pollution, there is still much we don't. Scientists all over the world struggle to understand the details. Although we frame our work as an effort to preserve "dark skies", there is much more to it than that. On the surface it seems like a matter of whether we can see the stars at night. Below that surface, it's about managing a massive public resource that affects everyone.

Every other year, researchers gather to discuss the latest results and find ways forward. These include the social and public policy dimensions of our work. The recent Light Pollution: Theory, Modelling and Measurement (LPTMM) conference attracted astronomers, lighting designers, ecologists, public officials and others. This year's edition of LPTMM focused on standardizing how we measure light pollution. It's clear that lacking a common vocabulary is holding back scientific discovery.

​This month we look at the case for standardization in light pollution research and why it matters. It's much more than a dry, pedantic matter of academic bookkeeping. Rather, it's a vivid and logical problem with many practical effects. And it may be the missing key to making our neighborhoods safer and lowering our taxes in the process.

As a form of environmental science, light pollution research has immediate applications. Artificial light at night (ALAN) harms our world in many ways. It is a known hazard to almost all living things including humans. It brightens the night sky, hampering our views of the cosmos. It has some kind of interaction with crime and public safety. Most importantly, it represents a waste of energy and of money.

We didn't start out with that in mind. Early lighting technologies were very inefficient. As our understanding of human vision improved, so did our lighting. But the last quarter-century has seen a revolution in how we light the world at night. Light-emitting diodes (LEDs) have made outdoor lighting cheap to own and operate. As a consequence, there is now much more outdoor lighting than ever before. That has sent light pollution skyrocketing worldwide.

​Many people are afraid of the dark. Various influences conditioned them to believe that a brighter space is always a safer space. The availability of cheap and highly energy-efficient outdoor lighting caters to that perception. But it also validates a fear that people feel viscerally even if it isn't always rational. Any attempt to change the trajectory of light pollution must confront this reality. 

Bright lighting creates harsh shadows where threats can hide. Its glare can be blinding to motorists, pedestrians, bicyclists and others. While intended to make the night more like the day, it can also leave people feeling exposed in outdoor spaces. But smart, well-designed lighting often yields a different response. It can help people feel secure and reassured when outdoors at night — even empowered. And it can achieve that by simply reducing or eliminating waste.

Outdoor light at night is a kind of shared public resource like roads or water. Poor-quality outdoor lighting is a colossal waste of energy and money. It is light paid for by taxpayers that often shines into bedroom windows or escapes into outer space. The goal of understanding light pollution is to design better lighting installations.

​Done well, this protects the fiscal bottom lines of towns and cities. It's also of interest to the world of private enterprise. There are reasons to believe that light pollution influences climate change. As "sustainability" is top of mind for many people nowadays, this matters more than ever. Demonstrating the true sustainability of good lighting design can be a powerful motive for change.

When researchers across disciplines can't understand each other's work, we lose real opportunities. The light-pollution research community experiences this now in an immediate way. To illustrate this, consider for whom we characterize the nighttime environment.

Light pollution research began decades ago in the astronomy community. As the most impacted "early adopters", astronomers considered skyglow a real threat to their profession. Long before there were space telescopes, astronomers built observatories far from cities. Clear, dry air on mountaintop sites was already good for their observations. Moving further from cities isolated their telescopes from interfering city lights.

The human perception of the night sky became centered in astronomers' measurement systems. They used tools tuned to the physiology of the human eye. Their goal was to characterize the night according to how people see it. That was a natural consequence in a science that began with the human eye as its only detector of light.

Of course, that happened long before we began to understand how ALAN affects other organisms. Our human experience of light at night can be very different than that of other animals. A migrating bird, a sea turtle, or a nocturnal insect doesn't care about human vision metrics. They can sense specific colors of light, like blue or ultraviolet, that humans may not register at all.

Lighting scientists and engineers largely adopted the astronomers' human-centric approach. They devised measurement quantities and units tied to the human visual response. Again, this makes sense if the point is to light the world to cater to human needs. But we're not the only ones who inhabit outdoor spaces at night. Biologists studying light pollution found themselves awash in the wrong measurement tools. To this day, they tell other researchers to stop measuring light like (and for) humans.

Astronomers publish their skyglow data using "human-eye units". Biologists can't use that data to figure out if, say, a local ecosystem is in danger due to ALAN. Meanwhile, skyglow researchers don't understand the metrics ecologists throw back at them. This breakdown stalls scientific progress. Biologists can't explain a species' needs to lighting engineers in accessible language. Engineers can't design better street lights that keep neighborhoods safe while protecting wildlife. Everyone becomes stuck in a never-ending loop of guessing. 

In everyday speech, "standard" means "basic" or "normal". But in science and technology, a standard is a kind of superpower. It is an official, universal prescription that everyone agrees to follow. And they don't happen by accident or simple acclamation. Instead, bodies like the International Organization for Standardization (ISO) bring together global experts to write the rules. Then, the public gets a chance to review them before they become official.

Standardizing measurements has a particular goal in mind: creating accountability. If a city or a scientist says "we are following the ISO standard," everyone on Earth knows exactly what that means.
As a kind of a rulebook, technical standards are only useful if people actually use them. Standards that don't get enough buy-in from end users risk being disregarded or even ignored. At the same time, no standard is agreeable to everyone. By design they are re-evaluated every few years. If users see a need for change, a process follows to revise the standard. In each case, the first version is just a jumping-off point.

To do this, technical standards rely on the International System of Units (SI), a kind of modern metric system. The SI is the ultimate global dictionary for measurement. It uses 7 base units and 22 derived units to measure everything in the universe. There's no need to invent strange new units to fix the light pollution language barrier. We need only take care to root our light measurements in a system the global scientific community already trusts.

In turn, standardizing measurements can improve public confidence in scientists and their work. High-profile disagreements among scientists can lead to belief the scientific method is failing. Yet disagreement isn't a sign of weakness. It’s how we test, break, and improve our ideas. In fact, it's science's greatest strength.

​But there's a big difference between arguing over theories and arguing because your rulers are different. Current confusion in light pollution science happens because researchers use different measurement tools. Standardizing our methods and reporting units helps clear up these unnecessary misunderstandings. When scientists speak the same language, it eliminates false disagreements. It also gives the public well-deserved confidence in the safety and resource advice scientists provide.

Standardizing measurements isn’t only neat bookkeeping for scientists in lab coats. It has practical, real-world effects that everyone should care about. If scientists standardize their language, they can give unassailable data to city planners. Decision-makers can in turn write better outdoor lighting policies. Those policies, if implemented well, can save money, reduce pollution, and improve public safety. It's much harder to reach these goals if scientists keep talking past each other.

How do we actually fix this scientific Tower of Babel? We can't expect everyone to wake up tomorrow and agree on a single language. So we need a plan.

An idea that emerges is a simple, two-part strategy. First, we propose forming specialized expert working groups across different sciences. For roughly a year, these teams will draft the basic ground rules for measuring light in their specific fields. Next, everyone will gather at an international pre-standardization congress. Think of this as a global peace summit for science. There, researchers can debate these ideas and hammer out a shared compromise. The result would be ready for submission to international bodies like the ISO to become an official, global standard. It’s a transparent, human process designed to get everyone speaking the same language.

​Ensuring an inclusive process, one that is both flexible and scalable, is crucial. If a durable standard results, the real work begins. We must then lobby for acceptance of the outcome in the research community. We must also socialize the results to encourage uptake and practical use of the standard. We'll know if we're successful by every scientific paper and government report showing adherence.
Achieving this result will take years, and it starts with admitting we need to try something different. The road to a standard for light pollution measurements leads toward a direction in which nights are better, safer, and maybe just a little darker.

Images of the Earth at night from space are an important tool to understand light pollution. They allow us to see the "big picture" across our planet at night and how it is changing. But satellite images aren't perfect by any means. Last year we wrote here about the limits of what those images can tell us. We also sometimes struggle to understand what the images mean in relation to the brightness of the night sky. And their designs and capabilities are far from ideal.

Still, satellite measurements are indispensable method in the researcher's kit. In the past decade they told a compelling story. In the mid-2010s, nighttime light emissions seemed to rise worldwide at about 2% per year. There were reasons to think this was a very low estimate. In 2023 an analysis of visual observations of the night sky showed the rate must be much higher.

​According to new research, the picture is even more complicated than we once believed. This month we dive into a recent paper led by Tian Li (University of Connecticut) that gives an unprecedented look behind the curtain. What the authors found was not entirely surprising.

The workhorse instrument for measuring "nighttime lights" is the Visible Infrared Imaging Radiometer Suite, or VIIRS. One of its cameras, called the Day-Night Band (DNB), has a sensitivity that allows it to measure very faint light. As its name suggests, it works well on both the day and night sides of the Earth. At night, it sees the glow of our cities as well as the light of natural phenomena like wildfires and the aurorae. Scientists used information about the artificial lights to learn about patterns of human activity.

The DNB has some limitations. It can only resolve areas on the ground about the size of a city block, nothing smaller. It flies over every part of the Earth at least once a night, but only at certain times. Most important, it does not see light in the blue-green part of the spectrum well (or at all). As modern outdoor lighting emits a lot in these colors, this sense of 'blindness' is significant. In particular, the DNB cannot see much of the light emitted by white light-emitting diode (LED) sources.

Previous studies published in 2016 and 2017 offered some insight despite these flaws. Artificial light at night (ALAN) is widespread across the world. In many respects, it has completely transformed the nighttime environment in some places. And it is growing in brightness and intensity faster than the growth of the human population. Still, until now our view was fragmented in time and space. And an analysis of a longer data series offers fresh insight.

The new paper by Li and coworkers considers the changes of every pixel in every DNB image from 2014-2022. Previous studies dealt only with long-term (monthly or yearly) averages to filter out influences like clouds. Irregular sampling of light data like this tends to "smooth over" short-duration changes. It also makes it difficult to sense whether changes are happening slowly or quickly. Earlier papers thus focused only on long-term changes, almost all appearing as increases.

Li's innovation is a new way of filtering out clouds and other contamination from nightly DNB images. Also, they accounted for the changing angle between the spacecraft and light sources on the ground. This better handles situations like light emitted 'sideways' from illuminated windows of buildings. And thanks to the orbital properties of the spacecraft, the DNB data include virtually all inhabited parts of the world.

What the researchers found is interesting, if not very surprising. Global light emissions increased 34% during the study period. But that surge masks large areas of dimming, which offsets about half of the brightening. The net result? Artificial lighting at night increased worldwide by about 2 percent each year. That is exactly the same rate measured with the same equipment during 2012-2015.

As a global average number, the result doesn't quite capture how dynamic nighttime lights are. According to the Guardian, "night-time light 'surged' in China and northern India along with urban development." Space.com noted volatility in places like Palestine (due to war) and Puerto Rico (due to natural disaster). Big apparent decreases in countries like France may be the result of policies meant to reduce light pollution (although the new research can't say for sure). And not all the change is due to the behavior of electric light. Citing NASA, the Guardian pointed to "intense gas burn-offs, or flaring, over central US regions" of oil and gas production. In short, the picture is complicated at best. 

When considered alongside earlier studies, the emerging picture is clear: they all point to a brightening world. The Nature paper by Li and colleagues doesn't change that broad conclusion. And a brightening world involves many social and environmental consequences.

In understanding this, there is an important analogy to global climate change. An objection to the evidence for climate change one hears sometimes is that certain places seem to be getting colder. And that's true: even in a world that gets warmer on average with time, some places get colder. But others get a lot warmer than the average. This is an expected consequence of adding energy to the Earth's atmosphere, raising the average temperature.

​The main takeaway from the Li paper is that patterns of change in light emissions over time and geography vary, and by a lot. The surprising conclusion is that "both brightening and dimming have markedly intensified over the past decade." That's one thing we didn't expect, nor can we quite explain it. And in many parts of the world, rates of both brightening and dimming are increasing together. More research is needed to understand why this is.

We need to keep beating the drum about ALAN and light pollution. The new data make clear that the world is leaning on the accelerator, not the brakes. There is a growing realization in the scientific community that light pollution is real pollution. It has harmful effects that can be mitigated through simple actions. When we undertake those actions, we know that they produce the expected results.

To the extent we might ever know what is a "safe" dose of ALAN, if such a thing exists, maps like these are our only way of knowing on a global basis which regions are exceeding it. This has meaningful value for everything from public health to ecological conservation.
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It also underscores the value of satellite data in this effort. Being able to say on the local level what's happening is crucial to inform lighting policy development. When we examine the data after the fact, it helps us understand whether policies work, and if so, how well. The images can even catch scofflaws as the ultimate "eye in the sky". 

Analysis methods will continue to improve and grow in complexity. There is every reason to believe that more insights wait to be extracted even from historical measurements. Yet we already have plenty of information in hand to know that it's time to move from study to action. For decades, satellites have helped characterize the problem. In the future they can show us which solutions work best.

But we need a new satellite mission whose design is driven by unanswered scientific questions. It should also have characteristics that make it best for testing our models and checking progress on light pollution-reduction actions. If those actions aren't working as intended, future studies like this may help explain why.

The new results for countries like France suggest how this might work. If the study analysis is right, decreasing light emissions there may mean that policy interventions are working. That, in turn, shows that long-term reduction of outdoor ALAN is possible. It's a pollutant that moves across jurisdictional boundaries with ease. Village-by-village policy making and planning is unlikely to ever get ahead of it.

Master lighting planning on regional scales may be the solution. That could extend to international agreements as well. We don't yet know if that will work, but the chances might be better if coupled to changes in environmental law. Europe is prime territory to test these ideas. One possibility is through the EU Nature Restoration Regulation. This requires EU member states to "stop, reduce or remediate light pollution in all ecosystems” as part of their national restoration planning. Satellite data can be an important part of assessing the status quo and checking up on how well actions are working.  A new European 'night lights' mission has been proposed and now awaits a funding decision.
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However that situation shakes out, it's worth staying tuned to this story. We still have much yet to learn.

The global dark-sky movement has achieved some notable victories. We have largely won the outdoor lighting hardware battle. The push for fully shielded luminaires has been successful. We have shown the efficacy of shielding as our best lever on reducing skyglow. But during the same period we saw a revolution in lighting technology nearly on par with the invention of artificial lighting itself. The arrival of light-emitting diode (LED) technology on the commercial market was a game-changer. LED has wonderful properties, controlling when lighting is on and where its light goes. It should have been a boon to light-pollution reduction efforts. Yet mostly that's not how it actually worked out.

Hardware has its limits. Shielding dictates where the light goes, but it doesn't control how much light is generated or when it is used. To make further meaningful reductions in skyglow, we have to look beyond the physical fixture and look at behavioral usage. Adaptive (or "smart") controls were intended to be that change. Carefully controlling the timing, intensity and color of lighting could be as much of a game-changer as LED itself. Yet few end-users implemented adaptive controls, leaving energy savings on the table.
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AI is everywhere right now. For better or worse, AI has some place in technology of the future. It is now paired with adaptive controls to optimize light use. This month we examine whether this phenomenon may help increase the uptake of adaptive controls.

LED lighting seemed to hold great promise when its commercial rollout began in the 2000s. In a time of increasing worry about carbon emissions and climate change, LED arrived at just the right moment. It was up to ten times more energy efficient than earlier technologies like incandescent filament lamps. Government agencies like the U.S. Department of Energy (DoE)  subsidized the transition to LED. After a few years, the cost of LED products plummeted.

But promoting energy-efficient lighting had an unintended consequence: it caused a "rebound effect". That is, as a technology becomes more efficient, it becomes cheaper to use, which actually drives up total consumption. [1] This was further fueled by public policy shifts mandating more efficient lighting. Decision makers rushed to install LED, replacing certain lighting systems such as street lighting.

The result fueled an increasing tendency toward over-illumination. The end users no longer felt the financial pinch of leaving lights on all night at full power. Cities directed cost savings into installing new lighting where none existed before. Earth's cities got brighter at night during the 2010s, accelerating the loss of the stars. [2] In the end, LED may have had none of the expected environmental benefits that its proponents claimed. [3]

By 2020, many lighting manufacturers offered hardware controls for new LED lighting. These controls change the state of lighting according to user needs. They range in nature from simple mechanical timers to complex, programmable schedulers. Their benefits seem good in principle. They help optimize efficiency of what amounts to a kind of industrial process. From a dark-sky perspective, this seemed ideal. After maxing out benefits of design changes (e.g., shielding), dimming and turning lights off became the new frontier.

The trouble is that most end-users didn't choose these controls. They were usually offered as add-on options and not integrated into the products. The main reason users opted against them was their added cost. Their low perceived value and high perceived friction further slowed adoption. Buyers tended to view the controls as unnecessary given the big jump in energy efficiency LED represented.
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Adaptive controls have something of a PR problem. The DoE says the main barriers to adopting controls are unfamiliarity with the technology, interoperability issues, and the perceived "fussiness" of programming them. [4] What they want is a tool that lets them turn the lights on and walk away. It has to be understandable to people who know little about lighting tech. They also want something more flexible than a binary on/off switch. 

The way around this obstacle is to take the burden of management off end users. In that sense, Artificial Intelligence (AI) may be the ultimate "set it and forget it" solution. If human hesitation and the annoyance of programming are the bottlenecks, AI is the frictionless solution. It bridges the gap between the need for adaptive lighting and the reluctance to manage it. Manual programming gives way to systems that learn traffic patterns, adjust to weather and predict usage. In this way, AI makes reducing light pollution easy.

Modern, AI-driven "smart" lighting systems use machine learning to process real-time data on their own. They can predict traffic flow, detect pedestrian movement, and even adjust light output according to weather conditions. The systems program themselves by sensing use patterns and applying the information to predict future conditions. As the circumstances change, they adapt. In that sense, "adaptive" controls come full circle and achieve their greatest potential.

If adaptive lighting is autonomous and easy to manage, AI could finally incentivize the widespread adoption of smart controls. This in turn could begin to slow the tendency to "over-deploy" LED lighting around the world. It also addresses the prevalence of full-night lighting in situations where it's unnecessary. [5]

Almost all efforts to reduce or extinguish unnecessary light encounter some resistance. AI-based controls may ease some of this concern. Through the use of dimmers, light remains available throughout the night on the basis of need. This is a more sophisticated approach than the use of motion-sensing switches alone. These tend to trigger at the wrong times and leave lighting on far longer than needed. AI systems can learn more about their environments. They adjust light levels, areas of illumination and other lighting parameters in subtle ways. We know that much of the utility of lighting for security purposes has to do with subjective "feelings of safety". AI could help improve users' perception of outdoor spaces as 'safe'.
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Some early experiments are proving hopeful. The European "SMARTLIGHT" project is  developing predictive, AI-powered adaptive street lighting. It promises 60–80% energy savings and big reductions in light pollution without manual human oversight. In Greece, Tvilight (a smart lighting controls company) installed an AI-powered adaptive lighting system across a major highway. It predicts traffic, expected weather, and road events to automatically brighten or dim over 9,000 streetlights. It does this without compromising driver safety. 

Industry-standard, fully shielded luminaires were a big win for the dark-sky movement. But hardware alone can't slow humanity's insatiable appetite for artificial light at night. The next great leap in light pollution reduction will come from intelligent control, not just physical fixture design.

The greatest influence AI may yield on the future of lighting is not mere energy savings. Rather, it's about removing the human aversion to engaging with complicated lighting controls. Systems can now predict needs and adjust supply of a public good. End users get their "set it and forget it" solution, and the nighttime environment gets a break. In this sense the solution may be a true win-win scenario.

It may furthermore realize the true cost savings proponents pushed two decades ago. If the cost of AI controls falls, they could finally bring the reduced carbon emission once expected. Decreasing skyglow would then be a fortunate side-effect. For as many problems that technology has solved, it tends to create others. The arrival of AI-controlled lighting systems may mean that the pendulum now swings in the other direction.
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Planning experts dream of cities of the future. They imagine light following human presence with ease instead of blanketing empty streets. Light glides through the urban fabric, creating inviting outdoor spaces. Instead of broadcasting light with reckless abandon, systems guide it with surgical precision. And as urban wildlife returns, there are a few more stars overhead. It brings promise rather than peril, and everyone can sleep a little better at night. 

1. Schulte-Römer, N., et al. (2019). The LED Paradox: How Light Pollution Challenges Experts to Reconsider Sustainable Lighting. Sustainability, 11(21), 6160. https://doi.org/10.3390/su11216160

2. Kyba, C. C. M., et al. (2023). Citizen scientists report global rapid reductions in the visibility of stars from 2011 to 2022. Science, 379(6629), 265–268. https://doi.org/10.1126/science.abq7781

3. Kyba, C. C. M., et al. (2017). Artificially lit surface of Earth at night increasing in radiance and extent. Science Advances, 3(11). https://doi.org/10.1126/sciadv.1701528

4. Poplawski, M. (2014, September). Emerging technology primer: Networked outdoor lighting control systems. U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy. https://www.energy.gov/sites/prod/files/2015/09/f26/ssl_outdoor-lighting-control-tech-primer_0.pdf

​5. Asif, M., et al. (2022). Adaptive Control of Streetlights Using Deep Learning for the Optimization of Energy Consumption during Late Hours. Energies, 15(17), 6337. https://doi.org/10.3390/en15176337

If you feel like automobile headlights have gotten brighter in the last few years, you’re not imagining it. Many now say the same thing. One need only refer to "those" headlights and most people know what one means. In fact, drivers in the United States and the United Kingdom have complained so often that both governments have started looking into the problem.

Most of the attention so far has been on glare and road safety. And to be clear, safety is important. It is, after all, the purpose of automotive lighting. But there’s another part of the story that many people don’t know about. Very bright headlights are impacting nighttime environment. Although lighted vehicles are only a temporary presence in that environment, they can have outsized effects.

​As the world continues to urbanize and vehicle traffic increases, headlights are becoming a source of light pollution. This month we look at how their light emissions move, spread far, and reach places that used to stay dark.

Every night, millions of cars send strong beams of light across the landscape. Unlike streetlights, headlights move and shine straight ahead, not only down. This means they can reach deep into forests, grasslands, wetlands, and other habitats that normally stay dark.

This kind of light pollution is different from the glow of cities or parking lots. It’s sudden, bright, and unpredictable. And because headlights are everywhere, they affect huge areas of land. That is true even for places far from towns or major roads. In some places, headlights are the brightest source of artificial light at night.
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We can even see some of this light from space. Highways trace out faint lines of light in satellite images. The example below shows such an instance.

Scientists already know that artificial light at night can confuse wildlife, change their behavior, and disrupt natural cycles like feeding and reproduction. But most research has focused on fixed sources like street lights. Headlights, which are both mobile and widespread, have been mostly ignored. For animals that depend on darkness to survive, these quick flashes of light can be a serious problem.

Today’s headlights are not the same as the ones from 20 or even 10 years ago. They changed as the arrival of white light-emitting diode (LED) technology revolutionized lighting. Several features of modern lighting make the problem bigger:

1. They’re extremely bright
Auto manufacturers design headlights to help drivers see far ahead. But this means they can shine much more brightly than natural source of nighttime light. Full moonlight has an intensity of 0.1 to 0.3 in a unit called a "lux". Yet a car headlight can reach around 25 lux — more than 100 times brighter. Even a short burst of light can disturb animals that are active at night.

2. They shine horizontally
Most outdoor lights point downward to reduce glare and limit light pollution. Headlights point straight ahead. This sends light directly into nearby habitats, where it can travel far beyond the road. By design, headlights also direct some of their light above the horizontal direction. The intent is to illuminate overhead road signs at night. Yet some of that light bypasses signs and goes into the night sky.

3. They affect huge areas
In Great Britain, headlight beams illuminate more than 2,000 square kilometers of land next to roadways. That’s a larger land area than all the natural grasslands in the region. Passing cars can thus affect even very remote places that are otherwise dark at night.

4. They give off a lot of blue‑rich light
Many headlights using white LED and xenon lamps produce a cool, blue‑white color. This is thought to promote driver alertness and aid low-light vision. But the blue component of white light is especially disruptive at night. It affects the secretion of melatonin, a hormone that helps regulate sleep and daily rhythms in both humans and animals. Blue light also scatters more in the atmosphere than other colors. For this reason it has an outsized effect on the brightness of the night sky.

5. They create sudden flashes
Headlights obviously don’t stay in one place. Each passing car creates a quick burst of brightness, followed by darkness again. Many insects and other nocturnal animals can’t adjust quickly, leaving them confused or vulnerable long after the car has passed. Near major highways and motorways, this confusion can persist for hours.

6. The problem is growing fast
Experts expect automobile traffic around the world to double by 2050. Millions of new roads will follow, some in places that have never had artificial light before. Headlights will reach deeper into wild areas, including some of the most important habitats on Earth. And this effect piles on top of light pollution from static sources. For example, many of those same roads will bring new and permanent roadway lighting.

The same features that harm wildlife also affect drivers. Very bright, blue‑rich white headlights can cause glare and make it harder to see at night. The aging eyes of older drivers are especially sensitive to this. This means that improving headlights can help both people and the environment. We don’t have to choose one or the other.

Poor outcomes are not the inevitable result of using the latest lighting technology for this application. As with other kinds of lighting, mindful design can mitigate a lot of the problem.

Let's go back to the premise underlying the existence of headlights. We do we use them? Because drivers need to see well at night. But brighter is not always better. There is no evidence to suggest that very intense, modern headlights are somehow safer than their predecessors. The key is making the best possible use of the latest lighting technology.

First, regulators should revisit existing standards for automotive headlights. Many standards assume the older, halogen-type light sources. Standards should be updated to reflect current technology. And governments should fund rigorous scientific research that supports evidence-based automotive lighting standards. This includes setting appropriate headlight brightness limits.

Second, automotive designs should make full use of adaptive lighting technologies. Modern headlights can dynamically adjust light beams to shine light only where drivers need it. This reduces glare and keeps light from spilling into nearby habitats.

Third, we need to dial back the momentum toward ever-bluer sources of light. Warmer‑colored headlights create less glare and are less harmful to wildlife. Again, research can help regulators craft rules that limit blue-rich light, protecting drivers, pedestrians, bicyclists and the environment.

Fourth, modern roadway design should explicitly consider light pollution. Transportation planners should think about how headlights affect the land around roads. New road projects, as well as upgrades to old ones, can include features that block or reduce light spill.

​And lastly, it may be time to reduce speed limits. Many traffic accidents, whether they occur during the day or at night, result from excessive speed. Lower speeds, especially at night, cater to longer driver reaction times. This, coupled with optimal traffic and automotive lighting design, maybe the recipe for safer streets.

Vehicle headlights are a growing source of artificial light at night. Yet they remain one of the least studied and regulated. As traffic grows and lighting technology changes, this issue will only become more important. It is creating new pressure on both cities and rural areas, as well as inhabitants of both.

But the worst outcomes can be avoided with adequate attention to the ideas discussed here. Further development of cutting-edge automotive lighting technology is one half of the equation. New research and thoughtful regulation of this lighting is the other.

​Protecting the night doesn’t mean giving up safety. With thoughtful design and good science, we can have safer roads for people and a healthier nighttime environment for wildlife.