Depending on where you live in the world, you may have seen them already. Some look like small computer monitors in shop windows showing opening times. Others are larger-than-life roadside billboards that seem like oversized televisions. They all use electronic displays to convey information, and at night they emit light. While these illuminated signs have different trade names, they are displacing earlier means of communicating messages at night. What does this mean for light pollution? Can these signs actually be good for the night?

There is no doubt that illuminated signs are in demand by advertisers and other users. They allow broadcasting messages, commercial or otherwise, at all hours of the day and night. To make messages legible at night, signs use various types of illumination. "Conventional" illuminated signs often involve upward floodlighting that can spill light past the sign edges and into the night sky. While a better approach lights from the top down and uses shielded luminaires, light spill and trespass can be a problem. Even light fully captured by the sign surface ends up, in part, lost to the sky due to reflection and scattering.

Digital signs make the sign surface itself luminous, usually through the controlled use of light-emitting diodes (LEDs). The light is not only bright and colorful, but also dynamic. The brightness of the message can vary to remain legible in conditions ranging from full daylight to total darkness. The displays can synthesize any color and rapidly change the assignment of light to individual pixels. The sign face can reconfigure to show a new message within a fraction of a second. Some displays can even show full-motion video.

These displays are big business. Market Research Future estimates that the digital billboard market will be worth almost $42 billion worldwide by 2030. Grand View Research expects that market value to increase by about 8% a year through the 2020s. LED technology is driving this growth. As equipment prices fall, more advertisers adopt LED for its configurability and high energy efficiency. It enables them to serve more ads at a lower cost of operation. In short: the future of outdoor advertising is digital. It's a future that consists of more lighted signs at night.

Like LED technology generally, this could be good or bad depending on the details. For this lighting application, as for others, LED has a lot of desirable characteristics. Its light is very directional, meaning that it doesn't tend to spread out much as it travels. Owners of displays can thus target the light in space to reach more of its intended audience with less waste. Further, the brightness, timing, and color are controllable, serving advertisers' needs with attention-catching visuals. This can mean using less light to convey messages compared to conventional sign lighting techniques.

But, like in many area lighting applications, LED is often deployed with little concern for light waste. Digital signs often have very wide angular fields of view in the name of maximizing visibility. They're often over-bright given the strong directional nature of LED. Results of a 2010 study suggest that owners of digital signs operate them at brightnesses several times higher than those of most conventional illuminated signs. [1] Viewers can perceive them as harsh, yielding a lot of glare that makes it difficult to read the message.

Digital signs broadcast their light sideways at angles that are bad for skyglow. Unlike other kinds of lighting, shielding isn't a convenient option for limiting this impact. Shielding would be so large to impose unacceptable wind loads on structures. Lack of vertical controls is the big problem. Designs direct much of the surface light upward and not toward advertisers' potential customers.

We don't have much in the way of hard data on these signs' contributions to skyglow or light pollution on the ground. But we can make some educated guesses based on what we know about them. While it is arguable that they may become an important new source of light pollution, the jury remains out on their exact effect.

There are concerns about the impact these signs may have on public safety, given their typical brightnesses. Data suggest that digital signs are more effective than conventional ones in drawing drivers' attention away from the road. [2] When messages displayed on digital signs change very rapidly, drivers may be further distracted. [3] Yet we still do not have definitive evidence that implicates digital signs in raising the incidence of vehicle crashes. [4]

It is important to distinguish the source of any presumed distraction. Is it the illumination, or is it the (changing) messages? Again, we don't know. The situation resembles that of road safety involving the use of mobile telephones. While hands-free equipment was first thought to be a safer approach, studies have not shown this to be always true. [5,6] It may be that talking on the phone while driving, rather than the manner in which one uses the phone, is most distracting.

Success in dealing with these concerns is a combination of technological innovation and common-sense regulation. Advertisers have an interest in ensuring that viewers see and read their messages. This can contribute in a positive way to reducing light pollution from digital signs. At the same time, viewers will not read messages on very bright signs. In fact, such signs may annoy them, causing them to form a negative opinion of advertisers.

There are some signs that sign manufacturers understand this. Some companies are testing technology that limits the range of angles in which digital signs are directly viewable. This is in part due to increased municipal regulation of digital signs in the U.S. An important Supreme Court decision in City of Austin, Texas v. Reagan National Advertising of Austin, LLC (2022) affirmed the right of cities and towns to regulate these signs.  Regulation ensures adequate stakeholder input and public oversight. And further design innovation will make for more efficient sign operations, lowering costs.

There are emerging best practices for how to operate digital signs in ways that don't harm the night sky. In 2019, the International Dark-Sky Association released its "Guidance for Electronic
Message Centers (EMCs)". This document suggests ways to operate and regulate digital signs to reduce their impacts on the nighttime environment. In the same year, the Illuminating Engineering Society introduced similar standards in its RP-39-19 document.

A body of knowledge is also emerging around how to regulate digital signs in the U.S. municipal context. For example, Scenic Utah offers a "primer" for communities that seek to enact ordinances regulating these signs. The ideas are simple: Limit digital sign brightness and size; the product of these is the total light emission of the sign. Place strict constraints on allowed sign brightnesses. Impose curfews prohibiting sign illumination during overnight hours. And wherever possible, restrict digital displays to single-color messages on black backgrounds. These rules reduce light pollution from digital signs while ensuring that their messages are clearly legible.

The rising market dominance of digital signs is an indicator of progress. As with previous lighting technologies, they present a challenge: to balance user needs against the equally valid need to protect the night from light pollution. Dark-skies advocates are working with municipal officials and advertising representatives. They are finding solutions that work for all involved.

Many communities have no rules on the books governing the use of digital signs. It is preferable to put such rules in place before digital signs arrive in your city or town. Contact us today to find out how we can help craft durable ordinance language regulating digital signs.

[1] Luginbuhl, C., et al. (2010). Digital LED Billboard Luminance Recommendations How Bright Is Bright Enough? White paper. http://www.illinoislighting.org/resources/DigitalBillboardLuminanceRecommendation_ver7.pdf

[2] Dukic, T., Ahlstrom, C., Patten, C., Kettwich, C., & Kircher, K. (2013). Effects of Electronic Billboards on Driver Distraction. Traffic Injury Prevention, 14(5), 469-476. https://doi.org/10.1080/15389588.2012.731546

[3] Belyusar, D., Reimer, B., Mehler, B., & Coughlin, J. F. (2016). A field study on the effects of digital billboards on glance behavior during highway driving. Accident Analysis & Prevention, 88, 88-96. https://doi.org/10.1016/j.aap.2015.12.014

[4] Oviedo-Trespalacios, O., Truelove, V., Watson, B., & Hinton, J. A. (2019). The impact of road advertising signs on driver behaviour and implications for road safety: A critical systematic review. Transportation Research Part A: Policy and Practice, 122, 85-98. https://doi.org/10.1016/j.tra.2019.01.012

[5] Lipovac, K., Đerić, M., Tešić, M., Andrić, Z., & Marić, B. (2017). Mobile phone use while driving-literary review. Transportation Research Part F: Traffic Psychology and Behaviour, 47, 132-142. https://doi.org/10.1016/j.trf.2017.04.015

​[6] Caird, J. K., Simmons, S. M., Wiley, K., Johnston, K. A., & Horrey, W. J. (2018). Does Talking on a Cell Phone, With a Passenger, or Dialing Affect Driving Performance? An Updated Systematic Review and Meta-Analysis of Experimental Studies. Human Factors: The Journal of the Human Factors and Ergonomics Society, 60(1), 101–133). https://doi.org/10.1177/0018720817748145

Many of us have heard of "light pollution", but we don't know much about it. For the most part, we associate it with the phenomenon called skyglow, which is the tendency of city lights to make it difficult to see the stars at night. In turn, skyglow tells us something about the amount of light at night we're using on the ground.

So if we want to reduce light pollution, we should ask how to go about measuring skyglow. We can not only track the degradation of the night sky but also the evolution of light on the ground by measuring the brightness of the night sky.

Almost 50 years have passed since the last major scholarly review of the causes of night sky brightness and the methods used to measure it. Our new Nature Astronomy review paper presents the latest version of our understanding and brings this science up to date. This month's post summarizes the most important parts of the paper. 

"Night" is the condition referring to the side of the Earth that faces into the shadow cast by our planet, blocking sunlight. Because our planet has an atmosphere, night doesn't begin as soon as the sun sets, nor does it end exactly as the sun rises.

Instead, after sunset and before sunrise an observer experiences "twilight". During this time, the atmosphere scatters sunlight toward the shadow and lights up the sky. Only when the Earth has rotated far enough into the shadow, as seen from an observer's location, does night properly begin.

We say that the night is "dark", but what do we mean? Most people think of a sky that is black, with stars, planets and the Moon superimposed on it. But there's more to it than that. Light from myriad stars in the Milky Way blends together and forms a bright band across the sky. Dust in our Solar System scatters sunlight toward the night side of Earth. In the polar regions, the aurora lights up the sky often during times when solar activity is high. Peering deeper with telescopes, we find even more light from distant galaxies and other sources. Under ideal conditions, the sky is never as black as it is when seen from outer space.

An example unfamiliar to most people is the "night airglow". This faint emission of light can happen on any night and is the result of physics and chemistry of atoms and molecules in the upper atmosphere. In photos like the one above it appears as an eerie green or red glow, sometimes showing a ripple pattern across the sky. Its visibility relates in part to the Sun's ultraviolet light shining on the daytime side of the planet. But unlike the aurora, observers may see it anywhere on the Earth at night.

These are all natural sources of light, but "skyglow" is something caused by human activity. In particular, wasted outdoor light causes it. As seen in the diagram below, rays of light emitted by outdoor light fixtures scatter and reflect from many surfaces. Some of those rays moving upward into the atmosphere scatter back down to the ground and make it difficult to see the stars beyond. 

Professional astronomers have collected data about skyglow for decades. But in recent years, advances in technology have enabled anyone interested in light pollution to make meaningful measurements.

There are several ways to sense the light of the night sky, from human eyes to cameras. The main differences among them relate to the amount of the sky sensed at once. The equipment we use to measure night sky brightness (NSB) falls into two broad categories: sensors that use either one or many light detectors.

"Single-channel" detectors use simple electronics to record the amount of light falling on a piece of semiconductor material. The best known of these is the "Sky Quality Meter" (SQM), an inexpensive device that is easy to use. It yields high-quality measurements and is portable, needing the power of only a single 9-Volt battery. Versions of the SQM and other devices are available that users can install permanently for long-term monitoring.

"Multi-channel" sensors are often some variety of digital camera. They use many light sensors packed into a small area to resolve the night sky in two dimensions. The human eye works in a similar way,  with retinal cells standing in for the electronic sensors of cameras. Human observers recording the faintest visible star make a measurement that is a kind of proxy for NSB.

Cameras give more quantitative information over large swathes of the night sky. The cost of such equipment has come down considerably in recent years. With a little training and inexpensive equipment, anyone can contribute data with clear scientific value.

Depending on the kind of sensor and lens involved, users can measure either the brightness of a small part of the sky or the entire sky at once. Different types of measurements record different information. For example, in any particular location, the main concern may be the growing skyglow influence of a nearby city. In such a case, it may make the most sense to measure only a small part of the night sky. 

Once the data is in hand, what can we learn from it? The answer depends on how many measurements are available.

Often, only one or a few observations are available from a given place on a single night. One might describe these situations as "impressionistic" measurements. They provided a limited amount of information, yet they enable people to draw some very general conclusions.

As in most situations, when it comes to NSB data "more is better". The real power of NSB measurement and monitoring comes when many hundreds or thousands of data points are available.

With dozens or more measurements, simple descriptive statistics can tell us a lot. These are numbers like the mean (or average) value, the median value, the high/low values, and the scatter (standard deviation) of the measurements. As the number of measurements increases, these statistics become more certain.

In cases where data taken over many months or years is in hand, we can take the analysis further. Complex representations can tell us a lot about how NSB changes both from night to night as well as over many years. Two examples of this appear below: the so-called "jellyfish" plot, and the heatmap.

When measurements taken nightly over a long period are possible, we can properly speak of "monitoring" NSB. This allows searching for trends in the data that can show trouble is on the horizon. Increasing NSB can be due to a single local installation of outdoor lighting, the influence of a single large city, or the collective effect of many nearby towns. In turn, dark-sky advocates can use this information to influence decision making in and near light sources of concern.

In Meditationes Sacræ (1597), the English philosopher Francis Bacon famously wrote that "knowledge itself is power." In confronting any social or environmental problem like light pollution, our ability to create change depends on how much we know about it. Understanding the light of the night sky is the first step in confronting the problem of light pollution. Measuring that light moves us from understanding to assessment. Monitoring its evolution with time adds detail that moves us toward solution.

Night sky brightness measurement and quality assessment are key components of dark-sky conservation. We guide clients toward understand the requirements and challenges of this work and how to get data of the best quality. Contact us today to find out how we can help. (And read our Nature Astronomy paper here.)

When you hear the word "conservation", what comes to mind? Maybe turning off a running water tap, or upping the thermostat a little in summer. We take such actions for a variety of reasons, such as lowering bills and reducing our dependence on natural resources. But what motivates us to do these things in the first place? And how might it be different when the focus of conversation is something intangible?

We sometimes encounter the idea of "conserving" dark night skies. The idea has been around at least since the early 1970s, taking the form of the protection of naturally dark places by astronomers. [1] At the start of the 21st century, the environmental conservation world began to take note. Now, at many parks and on protected lands, conservation professionals monitor the "quality" of night skies alongside the quality of air and water.

Those professionals often refer to the "objects" of their conservation efforts. Air and water are easy to understand as "objects". But what about the beauty of a natural landscape or the historical significance of the ground? Can a dark night sky itself be a "conservation object"?

Understanding that requires a little background in conservation theory. Conservation related to "resources" which are usually natural in origin. Some resources are renewable, and some are not. Some renewable resources lose their renewability due to human interactions. Humans consider something a resource because they assign some kind of value to it. Resources become objects of conservation when one or more influences threaten their integrity. The combination of value + threat makes the "object" a target for conservation to ensure it continues to exist.

In naming the conservation object here, we should consider the value and the threat. It also pays to think about the problem more broadly: the resource is best described as "nighttime darkness". A dark sky is a subset of that, because it's only half the landscape. The other half is the ground, where most concerns about harm to biology (including humans) exist.

Nighttime darkness has value along several dimensions. One model holds that objects fall into a space defined by value to individuals, value to groups, and scientific value. [2] The farther an object is from the origin of this space, the more likely it is to be considered a conservation object. 

People clearly find value in nighttime darkness. For example, dark night skies have inspired humans to create great works of art. Some people report meaningful psychological and/or religious feelings when accessing dark skies. And there is evidence that regular exposure to nighttime darkness supports a sense of wellbeing and better health outcomes. At the same time, dark nights have an "impersonal" value at a level higher than the individual. The relationship between natural darkness and humans is a kind of intangible cultural heritage. It also relates to the welfare of wildlife and ecosystems that depend on it. And as "reservoirs" of darkness, naturally dark places are important laboratories for scientific studies. Some sciences like astronomy are dependent on access to them.

The threat to this object of value is artificial light at night. It's not new; for at least 2,000 years people have observed the effects of light at night on plants and animals. The significance of that harm increased with the introduction of electric light about 140 years ago.  And an understanding of how it affects people has matured only in about the past half-century. The threat to nighttime darkness materializes in the form of light pollution, which now affects much of the world. [3,4]

This may all seem like an academic exercise. But there is a practical benefit to the kind of analysis that identifies natural darkness as a conservation object. Various bodies of knowledge, from environmental science to philosophy and ethics, help inform how to conserve it. The experience of practitioners over several decades shows us the best practices. And environmental history shows how framing the nature of the object leads to the most effective forms of advocacy and activism to protect it.

The trajectory of a conservation approach can go one of three ways: it can improve the value of the object; "hold the line" in its current state; or see the degradation of the object leading to a loss of value. How it evolves in depends on the severity of the threat; how the nature of the threat changes over time; and how the perceived value of the object responds to the threat. Rarely is all this determined in advance. Rather, conservation is an open system that interacts with the world in complex ways.

Lastly, what does this teach us about protecting the things we care about? Conservation of a resource involves a certain kind of "value proposition". It asks the question: why should people care? People and groups who have been deprived of natural darkness, often for generations, might not find value in the resource. They might decide that conservation efforts are too difficult, and the rewards of success too far away in the future to matter today. In short, they might decide that the perceived risks outweigh the supposed benefits. How can we change this?

To increase the value proposition, we must show clear benefits resulting from the behavioral changes needed to achieve conservation of the object. That may be the positive impacts of astrotourism on stagnant rural economies. Or it may be improved ecosystem resilience in the face of global climate change. People may come to see access to nighttime darkness as a factor that improves their quality of life. It could even be as simple as a desire to leave the world in better condition for the benefit of the generations that follow us.

When people come to see the value proposition of conserving nighttime darkness, they are more likely to support the changes that will achieve its goals. Often these behavioral "nudges" are small, reducing the sense of investment in what may be seen as an uncertain outcome. Yet, unlike in the case of other forms of environmental pollution, improvement of the resource is immediate following actions taken to reduce light pollution. Seeing immediate results can help sustain and further conservation efforts once conditions begin to improve.

The adoption of nighttime darkness conservation by environmental professionals is an important milestone along the road to saving dark night skies for our children and grandchildren. Achieving that goal involved elevating the resource to a high state of value and identifying a clear threat to its long-term stability. From there, the tools of the conservation trade can be adapted to protect it.

Many groups are now considering how they can write these ideas into their plans and actions. We can help articulate the value proposition to stakeholders and devise strategies for dark-sky protection suitable for any size business or organization. Contact us today to find out more.

This month we shine a figurative spotlight on scientific research into light pollution and dark skies. As a field of academic study, it is growing fast. In the past decade it has brought researchers together across many different disciplines and spawned its own conference series.

Two events in June highlight how prominent light pollution research has become. We recap them here.

​
We surveyed almost 4,000 scientific papers and reports in the Artificial Light At Night Research Literature Database. The goal of the report is to empower dark-sky advocates and the public with reliable, factual, understandable information about light pollution.

The report condenses the current scientific consensus on how artificial light affects seven key topics. These are the night sky; wildlife and ecology; human health; public safety; energy use and climate change; social justice; and satellite light pollution. Where gaps exist in our knowledge, we highlighted them as targets of future research.

"State Of The Science" finds the world transformed by electric light in less than 150 years since its introduction. Evidence exists for significant impacts in all the topical areas covered by the report. But it also identifies instances where the evidence is ambiguous and requires further scrutiny.

We used illustrations from the papers we cite to make certain points clearer. Also, we wrote the report in language that avoids jargon to make the contents understandable to more readers. Besides its value to dark-sky advocates in their education and outreach efforts, the report is suitable as a "leave-behind" for lawmakers and their staffers.

For a closer look at how and why we created this report, click here to watch a March 2022 presentation to the IDA advocate community.

Outdoor artificial light at night has transformed the Earth in ways we still struggle to understand. Despite its many social benefits, wasted outdoor light at night harms the environment and people. In that sense, the issue is a pollutant (outdoor light used with little caution) contaminating a natural resource (nighttime darkness). 

This idea is not news to anyone who has followed the environmentalism movement of the past half-century. Instances of major legislation protecting the environment from pollution have followed a more or less standard script: First, quantify the significance and the severity of the problem. Next, determine a "safe exposure" threshold. And finally, write policies that establish penalties when those thresholds are exceeded. This approach to reducing pollution has achieved success in many parts of the world.

So far, this model doesn't apply well to how the world treats light pollution. There is yet no agreement about what a "safe exposure" is for people, although we know that even tiny amounts of artificial light at night are hazardous to wildlife. For now, the conventional approach to reducing pollution isn't working.

Instead, the usual way that legal jurisdictions try to limit light pollution is by placing limits on the 'source' side of the problem. That is, they enact laws requiring shielding of lights or prescribing limits on light intensities. Some may limit the spectrum of the light to reduce specific environmental harm. Limited evidence exists that this sometimes works to reduce light pollution. But we can't yet point to any specific outdoor lighting policy and say that because of the policy light pollution changed by some amount.

Maybe we need to rethink altogether our notions about how to regulate outdoor lighting. By and large, our policies still cater to human needs first. And our current 'sustainability' paradigm mostly prioritizes the economy and society over the environment. Furthermore, light pollution doesn't respect political boundaries. Light at night emitted in one area can easily affect another place hundreds of kilometers away.

At the same time, dark skies are a manageable resource. The problem we confront is in search of a regulatory solution, not a technical one. What if the center shifted toward the nighttime environment itself, independent of whether any humans were around to experience it?

That's an idea that first took root in Western society about 50 years ago in the form of a legal framework called the "Rights of Nature". Its proponents suggested the best way to save the environment was to give a kind of legal status to nature itself, with human agents acting on its behalf. The Rights of Nature holds that nature has the right to remain in its inherent condition and be remediated if damaged. People not affected themselves by environmental degradation also have a right to bring suit on its behalf. It implies that natural resources are kind of public good worth managing in trust for the benefit of future generations.

A famous example of this is the Whanganui River in New Zealand, sometimes known as "the river that owns itself". In March 2017, the New Zealand government conveyed a legal status on the river like that of a corporation or a natural person. Two officials, one from Māori and the other from the NZ government, represent the river's interests in court.

So what might a dark-skies implementation of the Rights of Nature look like? It could begin with legislatures enacting resolutions identifying the values associated with dark skies. That value, enshrined in law, could one day prompt reconsideration of the current view of darkness as a resource whose exploitability is endless.

Going a step further, legislatures could insert statements of intent into bills, bylaws and ordinances. This provides guidance to judges who interpret laws. In turn, that could build up a body of case law that points toward an elevated legal status for the night. It can also connect dark skies to issues like social and environmental justice.

New international treaties may advance the idea of intrinsic rights for the nighttime environment. Treaties signed by 'coalitions of the willing' help establish the limits of acceptability. They can also impose pressure on holdout countries that brings their own national laws into eventual compliance.

Lastly, there are clear affinities between these issues and those important to Rights of Nature initiatives around the world. Joining forces with organizations dedicated to protecting nature can elevate the conversation. It will be important to keep dark skies in the foreground as world legal thought evolves around issues like climate change, habitat loss and threats to biodiversity.

Dark skies in the Rights of Nature context is a very forward-looking concern. Any gains are likely in the far future. For now, it offers a new way of framing the problem of light pollution and suggests innovative ways forward. There are many ways to address light pollution on the local level that leverage the many existing tools at our disposal. We can help clients navigate these challenges and come up with effective solutions. Contact us today to find out how.