Regular readers of the blog know that light pollution is a growing problem around the world. Each year, nights get brighter as humans deploy ever more outdoor lighting. This makes it harder to see the stars at night. It can also harm wildlife, threaten human health, and diminish the natural nighttime environment.

We know that much of this problem comes from wasted light. Lights are often too bright, shine where they are not needed, or stay on when they are not useful to users of outdoor spaces. Of course, this does not mean all outdoor lighting is bad. Lighting is important for safety, work, and amenity in public spaces. The challenge is using the right amount of light in the right places and at the right times.

Public policies can help reduce light pollution, but only if people support them. Many people want darker skies, but they also want safe streets, active businesses, and control over their own property. Any workable solution must balance these needs.

​One possible solution is the use of Lighting Zones. Lighting Zones guide limits on outdoor lighting based on the type of activity on a property and expectations for the availability of light at night. Different places have different lighting needs, and Lighting Zones try to match lighting levels to those needs. This month, we explore how Lighting Zones came to be, what their benefits and drawbacks are, and what new developments in this area mean for urban planning.

Lighting Zones emerged from ideas long used in city planning. Cities often divide land into zones, such as residential, commercial, or industrial areas. An overlay zone adds extra rules to these areas without changing the original zoning. The intent of land-use planning is to promote desirable development outcomes as well as more efficient uses of resources.

The idea is to match allowable activities on land parcels to their geographic situation. Compatible uses tend to cluster together. Zoning tends to isolate and restrict activities the public finds objectionable. In short, planners believe that zoning influences patterns of human behavior. Furthermore, the resulting changes are beneficial to society.

As applied to outdoor lighting, each Lighting Zone has its own rules for new buildings and outdoor spaces. City planners can then check if a new project follows the rules for its zone. This approach allows cities to focus on lighting without rewriting their planning laws.

But zoning rules can be hard to design and use correctly. Also, many urban planners don't learn about outdoor lighting in their formal education. They often know little about lighting technical information. As a result, outdoor lighting policies like ordinances and bylaws can be ineffective.

​The creation of Lighting Zones intended to make lighting rules easier to understand and apply. The idea originated from international standards promoted by the International Commission on Illumination, known by the French abbreviation "CIE". The Environmental Zones first appeared in a 2003 CIE publication intended to reduce obtrusive light at night. In 2011, these ideas were later expanded in the Model Lighting Ordinance (MLO). The result offered local governments a clear way to regulate outdoor lighting.

Lighting Zones are divided into five levels, from Zone 0 to Zone 4. These cover a wide variety of situations from areas with little or no outdoor lighting to very bright places, such as busy city centers or entertainment areas like the Las Vegas Strip. The table below shows the definitions of the Lighting Zones and how they relate to the CIE Environmental Zones.

Lighting allowances tend to scale up as the Lighting Zone number increases. The goal is simple: allow more light where people expect it, and less light where darkness is important. This system helps planners and decision makers set clear limits. Instead of arguing about every new light proposed, they can use the zone rules to guide their choices.

Lighting Zones have several benefits. They are flexible, easy to explain and match well with existing land-use zones. In some cases, local governments map them to their existing zoning systems. Lighting Zones help communities set clear lighting expectations for different areas. They can mediate dispute resolution as land uses change over time. And they are a tool local governments can use to push back against requests for exceptions or adjustments to development rules.

But there are also some drawbacks. Some places do not fit neatly into one zone. If zones are applied carelessly, areas may be given higher lighting limits than they really need. Over time, this can lead to brighter nights instead of darker ones. Some people also worry that Lighting Zones are too simple and do not capture real-world needs. Others may resist them because they do not want new rules or limits on outdoor lighting.

Many communities do not make use of Lighting Zones in their planning systems. At some level this is because of a lack of awareness that they exist. But even when planners know about Lighting Zones, they may hesitate to embrace them. They may find the distinctions between Lighting Zones unclear. In turn, they find it difficult to know when and where to apply them. Elected officials sometimes turn away from adopting policies they don't completely understand. They may also sense a lack of public support for this kind of zoning. 

The Illuminating Engineering Society, a U.S.-based professional organization of lighting engineers, promotes various lighting recommendations. Among its 'recommended practices' is RP-43 ("Lighting Exterior Applications"). 2026 will see a major update to this document. It's relevant to this discussion because RP-43 maintains the Lighting Zone definitions that first appeared in the MLO.

While the new recommendations are not yet published, they are public by way of the American National Standards Institute (ANSI) review process. We know that they contain a few amendments to the Lighting Zones. One major change is the addition of a Natural Conditions Zone. At last, this recognizes that the goal in some places should be to keep them naturally dark. These are places where the human presence at night is small or nonexistent. As a result, there is no expectation of permanently installed outdoor lighting. Where lighting deemed necessary, it should take the form of flashlights/torches and similar portable lighting.

​This is a turning point for the lighting engineering and design community. Before this update, the zone with the most restrictions was Lighting Zone 0. The definition of that zone calls for "little or no lighting" but does not exclude lighting altogether. Establishing the Natural Conditions Zone acknowledges that some situations call for a total prohibition of permanent outdoor lighting installations. As a result, the new RP-43 brings clarity to the Lighting Zone 0 definition. While Lighting Zone 0 still allows the installation of permanent lighting, its use is minimized by design. These updates help protect places where darkness is especially important, while still allowing bright lighting where it is legitimately needed.

Lighting Zones are a useful tool for managing outdoor lighting. When used carefully, they help protect dark skies while keeping places safe and usable at night. But for Lighting Zones to work well, they must be applied thoughtfully and supported by the public. As lighting technology and community needs change, the zones and their rules will also need to change. Right now, the biggest challenges are that many people do not know about Lighting Zones, and some resist new regulations. Better education and clear communication can help show that smart lighting benefits everyone.

​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.

Light pollution is increasing almost everywhere in the world. [1,2] We know that this has serious consequences for society and the environment. [3] Its rate of increase is faster than that of population growth in many countries. This implies that the rate of consumption of artificial light at night is growing. [1]

Researchers think that this results from the lower cost of operating light-emitting diode (LED) lighting compared to earlier lighting technologies. If this is true, it undercuts the claimed environmental benefits attributed to the high energy efficiency of LED. We don't yet know what this means for differences in energy consumption, if indeed energy savings are offset by the growth of new lighting.

​We also know that harms associated with light pollution are reversible. It does not persist in nature like other forms of pollution. When we deploy proven solutions, we see the reductions in light pollution that we expect. [4] Through concerted efforts, we can imagine a future in which it reduces in intensity according to predictions.

This is not only limited to slowing the further growth of light pollution. Activists are beginning to talk about 'restoring' natural nighttime darkness in some places. But what does this mean, and what would the world look like if it were successful? This month we look at the notion of nature restoration and what lessons the broader conservation movement has for dark-skies advocacy.

When we talk about 'restoring' nature, it's important to agree on what that term means. It is often discussed in the context of another word, 'rewilding'. It refers to reverting to environmental conditions resembling those that existed before human manipulation. One finds the term applied often in situations in cities where removal of development traces encourages natural processes to return. [5]

It is important to distinguish rewilding from another kind of restoration referred to as "Nature-based Solutions". [6] The International Union for the Conservation of Nature defined this term in 2006 as "actions to protect, sustainably manage, and restore natural and modified ecosystems that address societal challenges effectively and adaptively, simultaneously benefiting people and nature." [7]

But it's not always synonymous with ecological restoration. In contrast, one definition of 'ecological restoration' is "assisting in the recovery of ecosystems that have been degraded or destroyed, as well as conserving the ecosystems that are still intact". [8] The authors who suggested the definition argue that the rising use of the term 'Nature-based Solutions' "may partially be a rhetorical response to shifting priorities and terminology by funders of research and practice". Yet they say that Nature-based Solutions "reflect a genuine commitment to achieving societal benefit." While the terms are distinct, they "are similar and can be mutually supportive."

Why does this matter? Some scholars have criticized Nature-based Solutions as a relic of colonialism or even a form of greenwashing. [9] It centers humans, in the sense of achieving social benefits, over any intrinsic value nature may have on its own. It relies on truly sustainable environmental management, which is rarely achieved in practice.

It also implies that humans won't conserve something unless they value it, presumably for selfish reasons. In this sense, it follows the implications of a famous quotation from the Senegalese forest engineer Baba Dioum. In 1968, Dioum said "In the end we will conserve only what we love, we will love only what we understand, and we will understand only what we are taught." [10]

All these ideas proceed from the assumption that there is some value to nature restoration, whether for humans or nature itself. Appeals to human wants and needs may be a means to an end in this regard. Dark-sky advocacy often focuses on the purported human benefits of improved outdoor lighting, such as security, public safety, human health and more.

While advocates also point out the harm that light pollution poses to ecosystems, they tend to frame the argument in a way that caters to human motivations. Examples of this include focusing attention on so-called 'charismatic megafauna' like sea turtles or nocturnal insects that pollinate food crops. In this sense, advocacy efforts seem to align with Nature-based Solutions as a matter of pragmatism.

Efforts to bring dark night skies back to areas affected by light pollution usually take the form of "landscape scale nature restoration". The Scottish Nature Agency defines this term to mean "land managers working together to restore nature on a large scale, across multiple land holdings and resulting in multiple benefits for nature and people." [11] It further suggests that "this approach is more effective at achieving environmental, economic and social benefits than working in isolation, on smaller, single sites."

DarkSky International has pursued this for years through its International Dark Sky Places program. [12] The program can be described as Nature-based Solutions with two main goals. First, it aims to increase public awareness of light pollution and reward participating sites for taking steps to address the issue. The second goal — restoring natural nighttime darkness over typically large geographies — is more outcome-based.

The evidence for success in achieving the restoration goal is mixed. [13,14] In recent years it has put increasing emphasis on cities as a source of both problem and solution. Through new designation categories like its "Urban Night Sky Places", it advances the idea that restoration of darkness in more distant sites depends on changes in the lighting of cities. But this approach is still so new that we don't yet know if it works as advertised.

Would a stronger appeal to Nature-based Solutions still result in meaningful restoration of dark skies? One might look toward Attention Restoration Theory for clues. It holds that a connection exists between access to nature and total human wellbeing. [15] But for one thing, we don't know for certain whether the natural nighttime space is a "restorative environment".

It's also unclear whether experiences in nighttime darkness helps move the needle on nature restoration initiatives. That's particularly true given a broad (and maybe innately human) fear of the dark that stokes hesitation toward some nighttime restoration initiatives. It might be an obstacle to moving people to care about this aspect of nature to the point where they would give up something else they valued to protect it.

​Other social concerns can override the human valuation of natural spaces. A recent example is the U.S. migrant detention center popularly known as "Alligator Alcatraz". In mid-2025, this facility opened at a disused airstrip in Big Cypress National Preserve, a federally protected land in south Florida (and an International Dark Sky Park). Aside from concerns about light pollution due to detention activities at the site[16], activists alleged other environmental harms that were not subject to review or meaningful oversight. One might well ask whether the American public would have accepted this activity in a higher-profile U.S. national park like Yosemite or the Grand Canyon.

​Although public attention to light pollution has risen steadily for decades, it is still climbing the "hill of awareness". We have identified a collection of best conservation practices, and there is some evidence for their efficacy. Yet we're a long way from implementation in many parts of the world because it's just not a priority for most of the public.

This argues for a more top-down approach as compared to countries like the U.S., where outdoor lighting policy is distinctly local in flavor. At the same time conservation is often focused on larger landscapes where few people live. To not only slow the growth of light pollution around the world but also reverse the trend requires different ways of thinking.

What about tying restoration to legal requirements? The recently enacted EU Nature Restoration Law aims to do so, obligating EU member states to develop plans to restore at least 30% of habitats in "poor condition" by 2030, 60% by 2040, and 90% by 2050. It even contains some language about light pollution. [17] For now the law is forward-looking, and we don't know if it will yield good results.

Globally, the successful strategy may well instead be to "bend the curve" of light consumption per capita. That is the amount of light emitted in a territory per head of population. In earlier times, that figure seemed to be stable. The advent of LED, with its extreme energy efficiency, seems to have prompted its increase through what economists call "elastic demand".

But human behavior proves difficult to change through heavy-handed regulation. Instead, the more appropriate goal may be to change the human relationship to ALAN. We recently wrote about a combination of hard and soft law in the form of so-called "lightshed management" as a possible approach. It sets targets for light pollution reduction while engaging in extensive community outreach to nudge people toward different behaviors in terms of how they use outdoor lighting. Here, too, the idea remains a theoretical one only for the moment.

​Without targets — preferably binding ones — it is going to be difficult to achieve true restoration of nighttime darkness. Considering the motives for restoration carefully and asking critically whom they benefit is an important step. The implementation best practices remain mostly to be determined. The stakes remain high if we do nothing, but our confidence in successful results once we apply suitable efforts is equally high.

Light pollution is increasing over much of the world. It is a trend that goes back decades and shows no sign of slowing down. We wrote here about the situation as recently as early 2023. At that time, new research showed that skyglow was then increasing at a worldwide average rate of 10 percent each year. A much newer notion is the idea of 'light pollution' from space. We also wrote about that situation in 2023. The concern was then about the changing appearance of the night sky. 

Fast forward only two years, and a completely new concern is now emerging. What happens when satellites can turn night into day? The result is a novel threat we explore in this month's post.

We live in an era some that some call "New Space". This describes activities in outer space dominated by private commercial actors. It contrasts with previous decades when only national space programs could pay the high cost of launch.

That cost plummeted in the 2010s, enabling private companies to launch payloads into space. At first, the main service private satellites provided was global telecommunications. But as investor money poured into the industry, entrepreneurs began to come up with audacious new ideas.

One of those ideas is to harness solar power in space and send it to the ground. This takes different forms including converting sunlight to radio waves. A simpler concept would deploy large reflective surfaces in orbit around the Earth. These would redirect sunlight to the ground to illuminate solar power stations on the ground. The scheme only works near sunrise and sunset, when the reflectors are in sunlight but the sun has set on solar farms.

Proponents of this technology note that it can provide light for other uses. For instance, they say, it could function in place of street lighting over cities. It would provide an illumination level about four times the brightness of full moonlight. That could aid in disaster recovery when utility power is unavailable.

You would be forgiven for thinking this is the first time anyone has proposed such a thing. But it's not. In the Second World War, a group of German scientists at the German Army Artillery proposed building a Sonnengewehr ("sun gun"). They designed a focused beam of sunlight from an orbital reflector as an offensive weapon. And they expected the devastation to be akin to what the world later saw resulting from the U.S. atomic attack on Japan.
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In October 1992, the Russian Federal Space Agency launched the Znamya 2 satellite. Designed as a 'solar sail' testing a new kind of propulsion, the RFSA repurposed it as a 20-meter-wide solar mirror. It consisted of panels of stretched, highly reflective film that deployed after launch.

During a demonstration of the technology, it successfully directed a beam of sunlight to the ground. It yielded a spot 5 kilometers wide with the intensity of full moonlight. The beam swept across Europe from southern France to western Russia at a ground speed of 8 kilometers per second. Though weather along much of the ground track was cloudy, some observers reported seeing bright flash of light as the beam swept past them.

The RFSA tried another test of this technology in 1999 with a larger spot size and a brighter beam. The test failed when the reflective film panels tore after snagging a piece of the Progress spacecraft used to deploy the object. Although the RFSA planned future satellites with even large collecting surfaces, the 1999 failure was the death knell for the program.

More than 25 years later, the concept is again inching closer to reality. An American company called Reflect Orbital applied for clearance to launch and operate a test satellite in 2026. It consists of a thin-film reflector 18 meters on a side and a system to control its orientation in space. By changing that orientation relative to the direction of the Sun, it can direct a beam of sunlight toward Earth.

Like Znamya 2, its beam has a diameter of 5 kilometers on the ground, enough to illuminate a large solar power installation. The beam shines for about four minutes before the satellite disappears over the local horizon. The company plans to eventually launch a flotilla of thousands of these reflectors. That would enable continuous sunlight for about an hour after dusk and an hour before dawn.

Will it work? We don't yet know. The Russian test from the 1990s suggests that something like this is technically workable. But if it does, a host of concerns are expected to follow.

Some problems have to do with the idea of shining a beam of light with the intensity of sunlight onto specific locations at night. A simple calculation suggests that the reflectors will appear on the sky as sources several times brighter than a full Moon. Far from the beams, they'll still look like bright stars, and dozens of them may appear in the sky at any moment.

Scattering of light in the atmosphere will make the edges of the beams 'fuzzy'. The mirror-like surfaces of the reflectors will deteriorate with time due to exposure to the space environment. The beams of light they produce becoming more diffuse, spreading out and losing intensity. This may direct light well away from the intended targets of the beams. Some of that light may end up in ecologically sensitive areas.

As described above, the mirrors have to change their orientation in space as they pass over a given location. Although the company claims that the reorientation will happen quickly, it involves sweeping the light beam across the Earth at high speed. A 2000 study published in the Journal of the Royal Astronomical Society of Canada found that "space-mirror experiments reflecting sunlight to Earth can produce resolved images having surface-brightness sufficient to damage human eyes looking through telescopes or binoculars". Even if the flash is instantaneous, it could cause real harm to the viewer.

In a similar vein, these light beams could be a problem for aviation safety. Pilots have for years reported intense flashes of light from laser pointers on the ground shining up at their planes. At the altitudes of commercial planes, beams of sunlight from space will be larger in size and brighter than they appear on the ground. This could become a significant hazard for civilian and military pilots alike.

There is great potential for misuse of this technology. Sunlight could be weaponized in a way that conventional solar power cannot be. It may be directed toward people and communities that don’t want it. It could also be used to convey battlefield advantage in military conflicts. This adds another layer of complexity in deciding how the technology should be regulated.

The reflective material could be subject to fraying or other kinds of damage on orbit. They may shed material that becomes space debris. Over time, the satellites will inevitably fall back to Earth, whether from atmospheric drag or deliberate action to de-orbit them. Where, when and how they will come back down is not clear.
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Lastly, despite prognostications to the contrary, there is no “inevitability” about this or any other idea for furthering renewable energy sources through methods such as sunlight as a service. Improvements in battery storage are slowly improving renewable energy supplies at night. We may be better off deploying more solar panels on the ground, even knowing that there is a life-cycle cost for producing/recycling the equipment. 

"Greenwashing" is a label describing efforts made to persuade the public that an organization's products or actions are friendly to the environment. Usually they are not, and the greenwashing effort is deceptive.

That seems to be happening in the case of sunlight as a service. The sales literature is full of starry-eyed claims having to do with a purported social good. But it focuses on the notion of sustainability in a narrow sense: providing sunlight from space for "clean" electricity generation. It doesn't consider the full lifecycle of the project from launch to de-orbit.

It doesn't account for the negative externalities of directing light to spaces where it doesn't naturally exist at night. There is abundant evidence for the harms associated with artificial light at night. That in principle includes sunlight directed to the night side of Earth. It interferes with natural rhythms as much as sources of electric lighting.

At the same time, there is no national or international prohibition on this kind of activity in outer space. The international legal framework governing activities in space takes the view that 'what isn't forbidden is allowed'. Norms often change to discourage a harmful activity only when the harm has already been inflicted.

In that sense it resembles obtrusive space advertising, which we wrote about here recently. Dangerous activities in space can occur with only an ill-defined liability system on the other side.

It's unclear how serious any of this is, and projects like Reflect Orbital may not fly at all. Many such audacious ideas never become reality. Some are meant only to attract the intention of investors looking to make quick money as companies are bought and sold.
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It remains to be seen whether there is any successful business model for selling "sunlight as a service". Yet the lure of new wealth from space may prove irresistible. This is a challenge for defenders of the night everywhere, and one that is worth watching closely.

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.