We know a lot about the effects of light pollution on wildlife, the night sky, and in other areas but not as much about what it does to people. One can find some evidence for impacts having to do with physical health, wellbeing, and even social justice. Studies on mental health in particular are few, and most are about whether artificial light at night (ALAN) influences the occurrence of mental illness.

Meanwhile, as humans concentrate into cities, they become distanced from nature. Some scholars speculate on whether separation from nature can have an adverse effect. Might something similar exist having to do with loss of nighttime darkness and routine access to the night sky?

Social science has started to ask whether people experience a sense of grief or loss at environmental destruction.  The Australian philosopher Glenn Albrecht invented a word for it in 2005: solastalgia. Describing it as "the homesickness you have when you are still at home", Albrecht composed it from Latin and Greek words meaning 'comfort' and 'pain'/'suffering'/'grief'. It refers to both anxiety about the state of the environment both now and in the future.

In June 2023, the journal Science published an issue with a special section about light pollution. Some 50 years after the term first appeared in its pages, light pollution appeared on its cover. Six review papers presented a summary of what we know about this issue from scientific, social and legal perspectives.

In recent years, dark-sky activism and what is now called "community engagement" forged new connections among activists, researchers and others. Through this work I met Dr. Aparna Venkatesan, an astronomy professor and Co-Director of the Tracy Seeley Center for Teaching Excellence at the University of San Francisco.

Besides her passion for the the study of the early universe, Aparna is a tireless advocate for diversity, equity and includion (DEI) in science and society. We also share a keen interest in the social consequences of space policy, about which we co-wrote a paper published last year in Nature Astronomy.

We have had many discussions about these issues particularly since the dawn of the large satellite constellation era in 2019. We talked about all this in the broader context of loss of humanity's connections to the night sky. We also came to realize that the night sky makes up a kind of intangible cultural heritage, one worth protecting.

Aparna suggested a word that parallels solastalgia in its derivation and meaning. "Noctalgia" is a  neologism that combines roots for "night" and "pain" to suggest the sense of loss associated with the brightening of the night sky due to light pollution. In a broader sense, it encompasses any influence that changes the character of the night, including on the ground.

In August we published an 'e-letter' in Science reacting to the articles in the earlier special section and introducing noctalgia to the world. We also posted the e-letter to the arXiv, a repository of scholarly literature on astronomy and other subjects. The media picked up on the idea shortly after and ran with it. The amount of coverage surprised us (see here, here, here and here). Clearly noctalgia struck a chord.

Naming things can be an opening to talking about them with more honesty and authenticity. But we also hope that giving a voice to what some people now feel will help move them to take action. That action results from awareness that becomes a demand of society to take on and solve a problem. In turn, that relates to something called the 'issue attention cycle'.

Anthony Downs was an American economist who specialized in public policy and public administration. In 1972 he wrote an influential paper called "Up and Down with Ecology — the Issue-Attention Cycle". In it, he argued that to solve social and environmental problems they had to capture and maintain public attention. He also described a cycle of steps from identification of the problem to post-solution effects that can start the cycle over again. 

As people discover light pollution, awareness rises. According to Downs' theory, some of them will decide that a real problem exists. If it maintains prominence for long enough, a critical mass will form and people will begin demanding solutions from decision makers. Yet it's arguable that the global dark-skies movement is still climbing the "hill of awareness" and that we are not at the peak yet.

Even among those who become aware of light pollution, there's no guarantee that they will become part of this movement. Some who experience light pollution may write off the loss of the night as a consequence of progress and modernity. For example, people in developing economies may cite a need for outdoor lighting to enable safe transit at night and a nighttime economy. Given the colonial history in many such places, it's difficult to argue that they shouldn't have access to it. That's true even as we recognize the many ways that ALAN harms humans and nature.

Some people might be motivated to do something about light pollution once they give voice (and a name) to the loss they have experienced. But that presumes that they have something to lose in the first place. As the world continues to urbanize, fewer people grow up in places where they can see the stars at night. It remains to be seen whether people who never had access to dark night skies grieve something that to them was never 'lost' in the first place.

But that loss is especially acute for some people who have long suffered from deprivation. Indigenous, Aboriginal and First Nations people often live in places where the night sky is still accessible. In many instances, it looms large in their culture, folklore and religion. But these people often have little to do with creating the conditions that lead to light pollution. They also often have the least amount of political power in their countries and hence little ability to do anything about it. For many, the sense of loss is all too familiar.

There is an old saying about how the pace of change determines outcomes: Toss a frog into a pot of boiling water and it will leap out to save itself. But toss a frog into a pot of cool water, gradually warming it up, and the frog will swim around until it boils to death.

People often recognize the severity of problems at different points in time. Some are 'early adopters' of such ideas, while others are laggards that don't get on board until late in the game. And as our world changes, what society considers acceptable levels of risk may shift.

The loss of the night can prompt real, palpable grief in some people. But can noctalgia really prompt more people to take action on the problem of light pollution? We don't (yet) know whether the same is true of environmental problems more generally, or the role solastalgia plays. Meanwhile, people everywhere are straining under the weight of the many problems humanity faces. 'Crisis fatigue' is real, and it undermines efforts to solve those problems in definitive ways.

But solving the problem of light pollution turns out to be remarkably simple and cost-effective. We don't lack a technological solution — one is in hand right now. It enables us to light the world at night well for human needs while minimizing the negative effects all that light has on the environment. By reducing or eliminating wasted light, we could get a handle on the situation in short order.

Of more significance is that humanity desperately needs a win in the environmental realm. Were we to solve the problem of light pollution within a generation, the result might inspire confidence in out ability to take on bigger issues like climate change. But first, we have to finish climbing that 'hill of awareness' that moves people to action. If we do, it could be one of the defining environmental moments of the 21st century.

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

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

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

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

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

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

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

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

As usual, the scientific presentations were all high-quality and stimulated lively discussion. The main takeaways from the posters and talks include:
​

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

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

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

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

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

Like other social and environmental concerns, light pollution sits at the confluence of three streams. It has a technical aspect, informed by science and engineering. Activists pursue its solutions, in part by raising public attention to the issue. And it has direct input from the world of public policy, as solutions become laws.

To communicate with the public and decision-makers, dark-sky advocates must have access to the results of the latest research on artificial light at night (ALAN). But science results can be difficult for non-specialists to understand. It is particularly true of light pollution research, which borrows from many academic subjects. A newly released summary of papers published through 2022 aims to meet advocates' needs. It brings them up to date and helps them understand the latest research results.

To make scientific research more accessible, in 2022 DarkSky International published “Artificial Light At Night: State Of The Science.” The report distilled the contents of over 300 scholarly papers into a short, easy-to-read briefing. It grouped results into seven broad categories: the night sky; ecological impacts; human health; public safety; energy use and climate change; light and social justice; and space light pollution. It concludes by listing open questions that may guide research in coming years, explaining briefly the methodology by which the report was written, and providing bibliographic information for all sources of information.

When the report was first published, DarkSky understood the need for regular future updates. The number of papers on light pollution and related subjects published in recent years has steadily increased. We can see this in the number of papers added to the Artificial Light At Night Research Literature Database (ALANDB). This is a collection of citations curated by a group of light pollution researchers in Europe and North America since 2014. ALANDB entries include peer-reviewed academic papers, theses, selected technical reports, and conference papers.

Totals from the past 20 years of papers added to ALANDB show that, on average, the contents of the database have increased by roughly 22 percent per year:

In recent years, curators added an average of 430 publications to the database each year. The papers' diverse subjects cover several physical, biological, and social science topics.

A breakdown of the papers published in 2022 (below) shows that biology studies and papers about remote sensing of artificial light at night account for about 80 percent of all publications added to the database.

The updated report includes a survey of 457 papers published in 2022. We highlight a few results here:
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• ALAN in cities may disrupt the process that scrubs harmful ozone pollution from the air during overnight hours. Sunlight breaks down air pollutants to make ozone, but natural processes remove it during the overnight hours. Outdoor lighting may thwart this 'scrubbing' process and increase daytime ozone concentrations. (Shith, S., et al. Atmosphere, 13, Issue 11, p. 1844.)
• Mental and physical illness may be linked by a ‘broken’ circadian rhythm due to ALAN exposure. Circadian rhythms control many aspects of human biology. Interruption of these rhythms caused by nighttime light exposure may harm both physical and mental well-being. (Su, K., et al. Brain, Behavior, Immunity – Health, Vol. 26, p. 100533.)
• Residents of U.S. residential neighborhoods subjected to past racial ‘redlining’ practices are disproportionately exposed to ALAN. Satellite remote sensing observations suggest that certain neighborhoods in U.S. cities are exposed to more ALAN than others. Previous results shows that racial minorities comprise the bulk of the population of these areas. New work suggests that this may result from racist housing policies in historical times. (Motairek, I., et al. Local Environment, Vol. 28, Issue 4, pp. 518–528.)
• Switching off street lighting during overnight hours can reduce instances of theft from vehicles parked along streets. Petty theft from vehicles parked along streets at night decreases when routine overnight illumination of those streets ends. New evidence indicates that theft moves from those streets to others with overnight lighting. While lighting changes decrease overnight theft, they may simply "displace" it to daytime hours. (Tompson, L., et al. Journal of Quantitative Criminology, Vol. 39, Issue 3, pp. 603–623.)
• Light pollution threats to astronomical observatories are growing worldwide at alarming rates. The rapid proliferation of white LED lighting produces in the last decade explains at least some of this change. Protection of observatory sites relies on both effective regulation and increasing public awareness of the threats. (Green, R. F., et al. The Astronomy and Astrophysics Review, Vol. 30, Issue 1.)

The report finds evidence of significant harm to the night sky and wildlife ecology from light pollution on local to global scales. There are major concerns about how ALAN effects traffic safety during  overnight hours. While decades of laboratory studies established a link between ALAN exposure and human health, the influence of outdoor light sources remains unclear. And to the extent that roughly 80 percent of world electricity production relies on burning fossil fuels, wasted light at night from outdoor sources remains linked to climate change. This remains true despite the ongoing adoption of energy-efficient solid-state lighting.

DarkSky intends the State of The Science report to communicate these ideas to readers along with extensive source citation. It published the document under a Creative Commons 4.0 license, allowing users to adapt and reproduce its text. Its language is plain and non-technical, and its contents are arranged around seven main topics. In this way, users can read and understand the contents of any particular section in isolation from the others. And the report is available through the Zenodo open science preprint server. Users can cite the document by its Digital Object Identifier (10.5281/zenodo.8071915).

'State Of The Science' is a useful tool for dark-sky advocates and the public alike. It can help anyone better understand what scientific research results tell us about light pollution. In turn, it can bring the significance of the problem into sharper focus and inform actions taken to bring about change. 

Here we review the main elements common to many outdoor lighting policies and suggest contents that aim higher in each step up. We label these "Good", "Better" and "Best", where "Best" contains all of "Better", and "Better" contains all of "Good". We intend the suggestions here mainly for U.S. contexts, but the ideas may be adapted to legal systems anywhere in the world.

These lists are not prescriptive. In other words, there are combinations of items drawn from the different categories that might suit one place better than another. Careful consideration of local needs and preferences will tend to reveal them. Also, the lists are not exhaustive in their contents.

Statement of purpose

This is a short explanation, in plain language, of why the local authority establishes the policy. It can also contain recitals, otherwise known as "whereas" clauses. Although the stated purpose of a policy isn't legally operable, it helps guide its future interpretation. That helps judges in civil cases implement the law as its framers envisioned.

Good: Ensuring nighttime safety and adequate illumination; promoting orderly relations between neighbors; saving energy.
Better: Enhancing quality of life; increasing amenity; establishing nighttime ambience.
Best: Clearly identify dark night skies (and their enjoyment) as a valuable resource; recognizing activities like amateur astronomy and stargazing; protection of wildlife.

Definitions

Outdoor lighting policies inevitably involve the use of unfamiliar technical terms. Concise definitions are important to add clarity to the words of the policy. The Illuminating Engineering Society publishes a useful list of definitions of technical terms. In some cases it may be helpful to illustrate definitions with figures. Even cartoon drawings can reinforce complex concepts. And some jurisdictions add their own definitions of legal terms according to other requirements.

Good: A few basic technical terms such as shielding and color temperature.
Better: Further technical terms; figures illustrating some concepts like shielding.
Best: Meanings of certain common words ("and", "is", etc.) in context.

Applicability

These statements say in which circumstances the policy is operative. This means that where the law is applicable, outdoor lighting must follow it. They may also state when the policy does not apply, in what are usually termed "exemptions". These statements should be as specific as possible to prevent ambiguities that can make enforcement difficult.

Good: All new public lighting.
Better: Some private lighting (with limited exceptions); amortization with limited triggers
Best: All private lighting; amortization with a sunset date

Note that "amortization" means a process by which existing lighting that does not follow the law is brought into compliance. Amortization is "triggered" when one or more events occurs. For instance, if a property owner carries out major renovations, a compliance trigger may require that all site lighting be made compliant. In the best policies, exemptions for existing, non-compliant lighting should end on a future date. This allows property owners adequate time to make changes.

Main provisions

This section contains the real substance of the policy. It prescribes specific standards that lighting must achieve to be lawful. This is where policies often necessarily become technical in nature. Here is where a jurisdiction can enact the requirements we know to be most effective in reducing light pollution.

Good: Full shielding of most light fixtures; light color limitations; 'warranting' of public lighting.
Better: Full shielding of all luminaires; light trespass prohibited above a threshold; public lighting curfew; lumen density limits.
Best: Lighting Zones; light trespass completely prohibited; private lighting curfew; illuminance specifications.

Prohibitions

Certain kinds of lighting are so problematic or objectionable that some jurisdictions forbid their use entirely. This section declares those types of lighting and their applications to be unlawful. Again, clear definitions of terms may be needed to resolve ambiguities.

Good: Unshielded lighting; mercury vapor lamps.
Better: Searchlights and other high-intensity light sources, except as required in emergencies; laser light sources.
Best: Dynamically varying lights.

Communities may want to consider these further provisions for their outdoor lighting policies:

More items in Better policies

• Findings of fact
• Special applications (e.g., car dealerships; flagpoles)
• Permitting process for temporary lighting installations
• Lighting plan review and permits required
• Detailed enforcement process

More items in Best policies

• Explicit regulation of all public lighting
• Inspection process for permitting
• Outdoor athletic field lighting
• Illuminated signs

​In January, we wrote about new research showing that the world at night is lighting up fast. At the same time, something else is happening that may change the nighttime world as much. The orbital region around the Earth is filling up due to increasing activity in the commercial space sector. Thousands of new satellites, and the debris they create, may change the night sky forever. But how significant is the problem, and what can we do about it?

Satellites have been around for almost seven decades. For years, countries launched them one at a time for specific purposes. Most satellites served to relay communications across continents at the speed of light. In the 1960s, engineers began to experiment with flying small, coordinated groups of satellites. Called "constellations", these groups performed specific tasks like relaying time signals. This is the basis for modern conveniences like the Global Positioning System, or GPS.

By the end of the 2010s there were a few thousand satellites overhead. These ranged in altitude from a few hundred kilometers to about 37,000 kilometers. Those highest satellites, in "geosynchronous" orbits, can dwell indefinitely over any particular place. Their distance, coupled with the speed of light, made for somewhat slow communications. But times were changing. The cost of launching payloads into space was dropping.

​In 2019, the American company SpaceX launched the first group of satellites representing a new use of outer space. Called "Starlink", the project aimed to provide high-speed Internet to almost every place on Earth. The company plans to deploy up to 35,000 Starlink satellites by the end of the 2020s. Others, following suit, have proposed as many as 393,000 more. These so-called "megaconstellations" are unprecedented in the use of outer space by humans.

There are many concerns about how these activities in space will affect our planet. To maintain these large numbers of satellites in orbit, launches will become an almost daily event. Rocket launches produce materials that foul the air and water, and they can damage launch sites. Satellites coming back to Earth will deposit significant amount of metal in the upper atmosphere. And the current best practice in disposing of what returns to Earth is to dump it in the ocean.

Little in the way of international law governs these activities. The current legal framework descends from the Outer Space Treaty (OST). Signed in 1967, much of the treaty speaks to the peaceful exploration of space. It prohibits territorial claims on other worlds and the deployment of nuclear weapons in space. And it makes countries liable for damages caused by spacecraft launched from their territories.

But the OST does not envision uses of space like satellite megaconstellations. The governance system the OST establishes is slow to act. And countries downplay environmental concerns as they rush to cash in on the megaconstellation phenomenon. All the while, the risks of space debris are growing. Congested orbital space increases the chances of collisions between satellites. The space is also filling with debris shed by satellites and discarded items like used rocket bodies. These objects threaten new collisions and make space more dangerous. Some speculate that the generation of space debris could quickly spiral out of control.

​Astronomers grew nervous after the first Starlink launch. Strings of bright objects appeared in the night sky around the world. Reflecting sunlight to the night side of Earth, the satellites began appearing in telescope data. Radio transmissions from satellite to ground interfered with sensitive radio telescopes. The astronomical community organized a series of conferences in 2020-2021 to discuss the problem. They recruited participation from the space industry to find creative solutions to the problem. One result is the establishment of the Centre for the Protection of the Dark and Quiet Sky from Satellite Constellation Interference.

​There is another way in which these large satellite constellations may affect the night sky. The rules of optics dictate the size of the smallest object that an optical system can resolve. Telescopes on the ground can resolve objects that are a little smaller than a meter in size. Smaller objects are not resolved, but their light still makes it into telescopes (and human eyes) at night. The result is a faint, diffuse glow across the night sky. This raises the brightness of the sky background, much like skyglow from light sources on the ground.

In 2021, researchers published a simple model to quantify how much light this contributes to the night sky. They made estimates for conditions before the first Starlink launch in 2019. The results suggested that by that time, satellites and debris ('space objects') raised the sky brightness by 10% above its natural level.

​As the night sky gets brighter, it becomes difficult to see cosmic light from beyond. Raising the background level lowers the contrast  between the sky and objects like stars and galaxies. For casual stargazers, it means seeing fewer stars at night. They may also miss faint phenomena like weak aurorae and dim meteors. Professional astronomers stand to lose some of their data. This means either they do less science or spend more money to build even bigger telescopes. This may have serious consequences in coming decades.

Another group published a study the following year that identified small debris particles as the problem. While they're much smaller objects than satellites, there are very many more of them. Given their small sizes, even the world's largest telescopes can't resolve them. The scientists concluded that if the generation of new debris can be minimized, the effect on the night sky might be minimal.

​The expected effect from space objects is small for now. Compared to skyglow in and near cities, it's almost negligible. The problem will be most noticeable in the least light-polluted places, like astronomical observatory sites. But that depends very much on what the future of space debris production is like. If satellites don't grind each other into dust through collisions, the worst outcomes may be avoided.

A combination of design and operations improvements and public policy changes is likely needed. This may involve changes to our understanding of what the "environment" is by taking a fresh look at our policies. While some space companies are willing participants in these efforts, others have yet to come to the table.

There is still much about this story that causes alarm. The night sky is changing, both from light pollution on the ground and, to a lesser extent, from space. While the problem of ground-based light pollution has demonstrated solutions, we don't yet have the answers for satellites. In both situations, the decisions we make today as a society will most certainly affect the future of our night sky.