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.

We've all been there at some point. You're walking in a dark space at night, alone, maybe to your car in a parking lot. And a kind of fear seizes you. You can't see very well around you, so you don't know if there is someone waiting in the shadows. You get to where you're going as fast as you can, unlock your car door, get in and lock the door behind you. For a moment, you feel safe again.

My friend and colleague Nancy Clanton, a lighting designer based in Colorado, explains how the situation is even more acute for women. She told me about an incident once, some years ago, when she was in an unfamiliar city to attend a lighting conference. She had to walk alone at night along a dark stretch of road between the convention center and her hotel. Even with all her knowledge about lighting and darkness, she still felt uneasy being out there by herself.

She saw two people, both silhouettes, approaching. Like many people in the same situation, Nancy had to make a quick decision. Were they two threatening men? An innocuous couple? Something else? In her mind, at that moment, was born the idea of "lighting for reassurance". With a small amount of well placed light, she could have made a quick friend-or-foe determination. And if circumstances required, she could have made a quick exit. It would have changed the situation in a fundamental way.

There are many reasons that people use artificial light at night. For example, we light sidewalks and pathways to help people orient and find their way from Point A to Point B. We light roadways and "conflict zones" where different kinds of traffic come together, because we know that doing so saves lives. We like to add nighttime amenity to outdoor spaces, making them more inviting for activities like commerce. But we also liked it because many people believe that light at night deters or even prevents the incidence of crime.

Does outdoor lighting yield any real, positive influence on nighttime safety and security? Does it reduce criminal behavior? "The influence of outdoor light at night on crime is mixed," writes DarkSky International in its most recent annual report Artificial Light at Night: State of the Science 2024. "Some of the same studies that looked at lighting and traffic/pedestrian safety also considered nighttime crime incidence. Certain studies reported crime reduction when lighting is added to outdoor spaces. Others find either a negative effect, no effect, or mixed results."

​Whatever the ways in which lighting and crime interact, it's not like the effect of administering a drug to a person. That is, there is no sense that a dose X of the medicine always produces effect Y in the individual.

Crime and lighting seem to have a very context-dependent relationship. There are very many of what researchers call "confounding variables". These are influences unrelated to the study subject that might produce some kind of effect in the system. Without careful control of these variables, the researcher can draw an incorrect conclusion on the basis of observing the intended effect.

To continue the medical analogy, drug researchers try to remove differences among people in patient study samples. These include age, gender, geographic, location, and other factors that might produce a result that mimics what the drug should do. Failure to deal with these "confounders" means that one can be fooled into believing there is an effect from a drug that is in fact, unrelated to its mechanism of action.

It is also very difficult to carry out high-quality, well-controlled studies. Designing reliable (and replicable) lighting studies is challenging. There is not much research funding for this. Sometimes the sources of research funding are questionable. Researchers worry they may want to see some sort of pre-defined result from studies they support.

And there are instances where experimental design is just bad. For example, a 2019 study conducted in New York City housing projects claimed a strong relationship between high levels of light and decreased crime. The study looked at the effect of placing intense light sources on portable towers outside housing buildings and tracking changes in the incidence of crime in the immediate environment around them.

​To the surprise of few, crime dropped. But that's what happens when you treat people like criminals and light up their homes like they were prison yards: you get unreliable results.

What underlies concerns about outdoor lighting, public safety and crime is the unspoken element of fear. It is a powerful and underestimated motivator of human behavior. Our evolutionary heritage has given us limited abilities to see at night. As diurnal animals are active during the day, it made night a dangerous place for our early human ancestors.

Although we tend to think of fear of the dark as something that particularly afflicts children, many people as adults feel a deep-seated sense of terror toward dark places at night. How much we know about a place determines our sense of ease (or unease) about it. Because we are so dependent on our sense of sight, it's easy to feel that we lose control when we cannot see what is happening around us.

Psychologists have long understood that these influences have tremendous power in shaping our perception of the world. In recent years, social scientists have begun investigating what they call "feelings of safety". That is, they try to measure the degree to which people feel safe or unsafe in different situations that may involve danger.

It is important to know that feelings of safety are independent of whether people are actually safe. There are many instances in which people feel unsafe about a situation but the evidence shows that there was no actual danger.

There are ways in which feelings of safety can increase in dark places at night that lead people to accept lower light levels. This relates to a sense in which people feel trapped by their surroundings. They are looking for the exits, so to speak, in case danger suddenly emerges. Research shows that lower light levels are less acceptable to most people in any situation where they feel trapped. If there are clear opportunities to escape if needed, the acceptability of lower light levels begins to rise. Other work shows that most people prefer somewhat higher levels of outdoor light at night. Most prefer light that is cooler than warmer in color appearance.

​But the value of this extra light diminishes very quickly as light intensities increase. The relationship between feelings of safety and light intensity appears to be logarithmic. What that means is that as light levels increase, the amount of an increase necessary to produce some certain amount of increase in feelings of safety becomes larger.

​The biggest increases in feelings of safety happen in moving from situations where there is no light to those in which there is a very small amount of light. To raise feelings of safety by again as much requires increasing the light intensity by much more, often more than a factor of ten.

​The increase in feelings of safety flattens out at highlight levels. We don't quite understand why. One theory is that high intensity lighting makes people feel insecure by promoting the sense that they are on display. Bright lighting can create deep, dark shadows between objects that obscure those spaces. A person moving through an outdoor space at night may not be able to tell whether there is a threat hiding in those shadows.

​The glare from very intense lighting sources also has a disabling effect on the viewer. Glare causes the pupil of the eye to contract, which reduces the depth of field of vision. It conveys a distinct disadvantage to the viewer. And it's the same "prison yard lighting" effect in the New York study mentioned earlier.

That's where "lighting for reassurance" comes in. It's an outdoor lighting ethic still new in the design community. While traditional design holds that more is better, lighting for reassurance asserts that better is better. Often that's less light chosen with a strategy in mind. The goal is to improve outdoor visibility at night and help users of spaces discern where threats might be.

​In particular, it makes use of the incredible properties of human vision, even at low light intensities, to see very small changes in contrast. It ensures that all potential safety hazards are clearly indicated. It also means not going overboard with lighting levels to the point that it becomes a disability for the viewer.

It also makes outdoor spaces at night more inviting to other users of those spaces. People generally tend to feel more unsafe when they are alone in such places at night. As more people fill outdoor squares, streets and other places, they begin to feel more safe in the presence of a crowd. This couples with the popularity of using outdoor light at night for aesthetic purposes. This can include lighting of building façades, statues and monuments, and other landscape features to enhance the sense of nighttime placemaking. And it avoids creating glare to the greatest practical extent.

The task is now to communicate this to more lighting designers. They don't usually learn it either in their formal education or as part of their praxis. We also have to change how lighting designers and engineers think about the concepts of minimum and maximum lighting levels. Right now, lighting standards generally tend to indicate only minimum lighting levels for various lighting applications. This is a belief, not always supported by evidence, that only certain minimum values are "safe". But it is often not clear why those values are "safe" while other values are not.

​It also does not take into account the idea that lighting can be too bright in some cases. That can create its own security problems. Organizations that make outdoor lighting standards are just beginning to embrace the notion that along with recommended minimum lighting values should come corresponding maximum values. The right lighting levels would make Goldilocks herself feel safe at night because they're neither too low or too high. They're just right.

What can we learn from all this? For one thing, many people experience fear of nighttime darkness, and that fear is visceral. We shouldn't tell them that they are wrong to feel fear because we have data that somehow show that their fears are unfounded.

It's also the case that feelings of safety are very powerful. We should recognize this and leverage that fact in outdoor lighting design. Furthermore, the human eye is an underrated detector of faint light at night. That said, lighting design often does not fully exploit its amazing properties. Instead, and as lighting has become much cheaper than ever to consume, design has pushed light levels very high.

The result is that the way we do lighting design now often does more harm than good, even though its practitioners clearly want to do good. What we can do for them is to help them put in place better design through lighting for reassurance. It combines the best of what scientists tell us about lighting with the power of psychology.

​Together, we can make outdoor spaces at night that are truly more safe while also helping people in them feel safer. If we overcome the fear that now leads to demand for brighter outdoor spaces, we'll increase support for measures that gradually draw down light pollution. To do so would be a win for all involved: for people, for the environment, and for the night sky.