A walkthrough of what research says about streetlighting and crime
This piece explains the evidence on street lighting and crime as part of Rubber Meets Road: Lighting, a Vital City-Center for Justice Innovation series on lighting New York's streets to make them safer. The series also includes a summary of the Rubber Meets Road project, a summary overview of the problem and solutions, a detailed policy primer, a design deep-dive on what well-lit streets should feel like, maps overlaying crime with satellite-measured darkness and 311 outage complaints, and a proof-of-concept app for reporting dark blocks.
In her seminal 1961 book, “The Death and Life of Great American Cities,” Jane Jacobs argued that the vitality of urban life depends critically on the design of communal spaces. With respect to public safety, she argued that the police, while a critical input into crime control, cannot make a community safe all on their own, and that sustainable safety is ultimately created by “an intricate, almost unconscious network of voluntary controls and standards … enforced by the people themselves.” In short, when public space is used and monitored by members of the public with the support of the police, these spaces are made safe for the public to enjoy. On the other hand, public spaces that are hidden from prying eyes — such as public housing stairwells or blocks where law-abiding people dare not venture — can become hot spots for crime and disorder.
Jane Jacobs’ central insight was that the most effective crime control strategies enlist members of the community to coproduce public safety alongside the police — a task aided by policymakers who can help to design public spaces that are defensible. In urban planning, the study of how public spaces can be engineered with safety in mind is known as CPTED (pronounced SEP-TED), an acronym for “crime prevention through environmental design.” Among social scientists, the term of art is “situational crime prevention,” acknowledging that crimes are implicitly a function of a motivated offender, an attractive victim and the right situation.
CPTED-inspired interventions are highly variable and include efforts to remediate blighted properties, find alternate uses for vacant lots, remove trash, better maintain public infrastructure, promote the use of surveillance cameras and design spaces that have better lines of sight, among many other varieties. Some of these interventions are a question of urban design and call upon the skill sets of architects and engineers. Others are related to the more mundane but critically important task of maintenance. As James Q. Wilson and George Kelling remind us in their seminal 1982 essay, “Broken Windows,” when public spaces aren’t maintained and property damage (e.g., a broken window) is allowed to proliferate without remediation, a signal is sent that no one cares, so broken windows cost nothing — a state of affairs that ultimately leads public spaces to be taken over by those with nefarious intentions.
While many situational crime prevention interventions are worth investing in and studying, this white paper focuses on improvements in street lighting — perhaps the oldest form of situational crime prevention.
Street lighting and human civilization
Street lighting is undoubtedly one of the earliest forms of situational crime prevention — or any type of crime prevention for that matter. As far back as antiquity, people have understood darkness to mean danger, and streetlights have been around, in one form or another, for millennia. Recognizing the value of ambient lighting during nighttime hours, extensive systems of oil lamps were used to improve safety at night in the Greco-Roman world. After a late-night dinner party, Romans would travel back to their homes on illuminated streets, not much different from today. While lasting evidence is scant, it is probably reasonable to conclude that street lighting is an idea nearly as old as civilization itself, an essential public safety strategy that evolved alongside the world’s first cities and, notably, thousands of years before the world’s first professional police forces in the 18th century. The idea that lighting means safety is both intuitive and universal. Even before humans settled in fixed location, it is easy to imagine hunter-gatherers feeding their campfires throughout the night, adding a source of light to ward off animals and better recognize any attendant threats from other human beings.
By some accounts, street lighting was introduced in the United States by Benjamin Franklin, who designed his own candle-based streetlight, first used in Philadelphia as early as 1757. David Melville demonstrated gas street lighting in Newport, Rhode Island in 1805, and Baltimore became the first U.S. city with municipal gas streetlights in 1816. And in 1880, after the invention of the electric light bulb, Wabash, Indiana, became the first U.S. city to use electric street lighting. Today, while there is substantial variation in their usage and intensity, streetlights can be found in varying degrees of abundance in every city in the United States and throughout the rest of the developed and developing world.
However, the number of streetlights, their brightness and the evenness of the light they provide continue to vary substantially across different areas within a city as well as between cities. Most U.S. cities still rely on legacy streetlights, which provide dim yellow light, focused intensively on the area just beneath the light fixture. Recently, a number of cities, including Chicago, Los Angeles, Philadelphia, Washington and Dallas, are switching — or have switched — to LED lights, which provide an experience of brighter and more even lighting.
Despite investments in lighting, ultimately there are streets in every U.S. city that are simply not very well lit at night, which has led to a natural question: Would improvements in street lighting lead to improvements in public safety? On the one hand, given the potential benefits of lighting, it seems intuitive that the answer would be a resounding yes. On the other hand, if we think of people who commit crimes as highly motivated to do so, then perhaps a modest improvement in lighting would generate scant deterrence. The next two sections of this essay provide a high-level overview of how lighting might affect public safety as well as a summary of the evidence, including a discussion of what we do not yet know.
Theories of change
The presence of ambient lighting can affect crime through numerous channels, each of which may operate by changing the behavior of potential offenders, potential victims, community members, police officers or any combination thereof.
Perhaps the most obvious way street lighting can influence crime is by increasing the perceived risk of being caught in the act by a patrol officer, bystander or surveillance camera, thus deterring people from engaging in criminal activity in the first place. Lighting can also affect the incidence of crime by changing the behavior of potential victims. Darkness is thought to generate a sense of insecurity because it decreases visibility and recognition at a distance, creating blind spots, shadows and potential places of entrapment. To the extent that better lighting enhances what people are able to see at night, it may empower them to mitigate a potential threat by taking an action as simple as crossing to the other side of the street or doing something else that makes them a more difficult “mark.”
There are other, more nuanced perspectives on the role lighting may play in the generation of public safety. These theories emphasize how investments in improving neighborhood conditions strengthen community confidence, cohesion and something known as “informal social control.” Specifically, when a place is perceived as cared for, it tends to be more welcoming to law-abiding people and less welcoming to would-be offenders. Blocks, intersections and green spaces frequently traversed by community members are generally less attractive places to deal or use drugs or for gang members to hang out, for example.
If better lighting reduces fear and brings more people outdoors at night, it may give rise to two potentially countervailing effects: On the one hand, more outdoor activity means more “eyes on the street,” potentially deterring crime by increasing the perceived risk of apprehension or through the types of informal social control that are a mainstay of the broken windows theory. On the other hand, more human activity means a greater supply of potential targets.
To the extent that enhanced lighting increases not only the perceived but the actual probability of apprehension, it might also generate incapacitation effects, where crime falls due to more imprisonment. This happens if better lighting makes it possible for the police to gather better evidence and make more arrests. While crime reduction by any means is a welcome outcome, it is important to remember that deterrence is cheap relative to incapacitation, which requires municipal and state governments to finance the considerable costs of arresting, adjudicating and confining offenders. As such, the efficiency and therefore the scalability of a given crime-control strategy like improved street lighting depends on the relative magnitude of its deterrence effects. Indeed, if the deterrence effects are sufficiently large, it is possible for a crime control strategy to reduce both crime and incarceration, producing a “double dividend” in which two costly outcomes — crime as well as resources allocated to crime control — are simultaneously minimized. That is always the outcome we want.
Empirical evidence
In thinking about the importance of ambient lighting in maintaining public safety, a natural place to begin is to consider the effects of street lighting’s great rival: the sun. While the sun’s movement is governed by the laws of physics, its relationship to time is man-made and therefore subject to government policy. Twice per year, daylight saving time generates a revealing natural experiment in the public safety value of lighting. Consider that as soon as clocks are set forward, a 7 p.m. walk that used to take place during daylight hours becomes a nighttime endeavor. Likewise, when the clocks are set back, what was formerly a nighttime excursion suddenly happens in the light of day. Researchers in the United States and Chile have studied what happens to crime, particularly street crime, during these controlled shifts, and their findings are what we would expect: A reduction in daylight leads to an increase in crime — powerful proof of concept that more ambient lighting leads to greater safety.
In contrast to these studies of daylight saving time, most academic literature studies discrete interventions that typically add new streetlights to an area or enhance the quality of the lighting already present. Areas receiving improved lighting are compared to plausibly similar control areas that experience no upgrades in lighting, and the relative change in crime is computed using a research design known as “differences in differences.” A comprehensive review by Welsh et al. (2022) of over five decades of research found that street lighting interventions reduced crime by an average of 14% across 21 research studies in which the comparisons being made were regarded as credible.
Notably, the entire body of literature includes just one randomized controlled trial — the gold standard in research that has become a mainstay of pharmaceutical studies and is equally powerful in assessing the impact of public safety interventions. That study, which evaluated the addition of portable temporary light towers in New York City public housing communities during the spring and summer of 2016, found that the added lights resulted in a 36% reduction in felony assaults and robberies during nighttime hours. Follow-up work from this trial found that enhanced outdoor lighting led to reductions in both crime and arrests in the intervention areas and that the beneficial effects of lighting in these communities endured for at least three years.
Does lighting shift crime to other locations?
A central question in studying any place-based intervention, be it street lighting, trash cleanup or additional police presence, is whether the intervention will genuinely reduce crime or simply displace crime to another location. From a scientific perspective, genuine crime reduction and displacement are equally interesting insofar as either effect provides evidence that crime is sensitive to lighting or whatever is being studied. But from a policymaker’s perspective, the difference between genuine crime reduction and displacement is critically important, as spending money merely to spread crime around a city is not a particularly attractive proposition.
As a general matter, criminological research has demonstrated that displacement is more of a theoretical concern than a reality. Because crime is so intimately tied to social context, and because the people who commit crimes tend to be so strongly tied to a small and familiar set of places, most place-based evaluations have not found evidence that crimes are pushed to alternative locations. Research that has studied the addition of lighting to entire neighborhoods reaches a similar conclusion — that better lighting tends to reduce crime in focal areas without causing crime to spill out to adjacent communities.
When it comes to street lighting, though, there is some additional nuance to consider. This has to do with the sometimes hyperlocal nature of lighting, which can vary tremendously from street to street. Two research papers speak to this nuance and find suggestive evidence that poorly designed lighting interventions could simply push crime around the corner rather than lead to genuine crime reductions. A study of streetlight outages in Chicago considered the effect of electrical outages and spent lightbulbs that caused short-term disruptions to municipal street lighting. Essentially, an electrical failure or a spent bulb causes a street to go dark for several days before the issue is fixed. This paper analyzed changes in reported crimes before, during and after 300,000 streetlight outages and found that outages caused nighttime crimes to spill over into nearby street segments, with the greatest impact on robberies and auto thefts. The likely intuition here is that few people wish to walk down completely dark streets, so human activity — and crime — were reallocated to better-lit streets. While, in this instance, the better-lit streets received more crime, the broader lesson is that crime can, in fact, be responsive to changes in lighting on a street-by-street basis.
A similar study of the Oxfordshire, Reading, West Berkshire and Wokingham municipalities in the United Kingdom examined what happened to crime after local authorities began to reduce the amount of street lighting at night to save energy costs and carbon emissions. Consistent with the Chicago research, the study found that crime increased significantly on street segments adjacent to those shut off at midnight to save energy costs. The study also found that areas adjacent to streetlights that replaced yellow lights (high-pressure sodium, or HPS, bulbs) with energy-efficient white lights saw nighttime crime decrease by 14% and increase by 13% on adjacent streets.
The central theme across these studies is that discrete shifts in street lighting — on a street-by-street basis — have led to behavioral adjustments, raising concerns that piecemeal lighting upgrades could simply displace crime rather than produce a genuine, scalable improvement in public safety. In order to maximize the public safety benefits, policymakers should do their best to upgrade lighting on a neighborhood-by-neighborhood basis.
Will lighting scale?
Taken as a whole, research that studies improved lighting in communities has found beneficial effects. However, an enduring question is whether improved lighting can have effects at scale — that is, whether a citywide improvement in street lighting will lead to a citywide reduction in crime victimization. At-scale impacts are elusive in policy research. Indeed, there are numerous programs that appear to lead to important improvements in a small population served by the program but which are difficult to deliver to a larger population due to some rate-limiting step, such as the scarcity of transformational leaders or the difficulty of hiring a large number of high-quality employees.
Lighting has several attractive properties when it comes to operating at a meaningful scale. The technical know-how involved in installing 1,000 streetlights is generally no different from what is required to install 10 streetlights. Similarly, delivering high-quality lighting is mostly an issue of a city’s capital budget and does not require the same degree of nuance and expertise as, for example, delivering culturally appropriate services to at-risk youth.
Does lighting scale? The daylight saving time papers — which study crime across entire cities when there is more lighting — hint that it can. But, for a long time, empirical tests remained elusive. In the last three years, empirical tests suggest that lighting can have at-scale impacts. There are now four evaluations of improved lighting across an entire city. All four evaluations study the change from legacy street lighting to LED lighting, which produces light perceived to be brighter and which, critically, provides considerably more even light across a street, with far fewer dark spaces between streetlights. Research in Mesa, Arizona; Philadelphia; and Washington, D.C., found that as lighting rolled out to different communities citywide, crimes fell — notably, in Philadelphia’s case, including shootings. In contrast, similar research in Dallas did not find an impact of lighting on firearm offenses, which was the only outcome studied. Of note, since firearm offenses in Dallas are statistically rare, this study was probably underpowered to detect effects of similar size to those seen in Philadelphia. It is also worth observing that while Philadelphia is a pedestrian-oriented city, Dallas is more car-oriented and, as such, might offer a more limited scope for lighting to make a difference.
Remaining controversies and future directions
In 1997, a National Institute of Justice report to Congress, authored by several of the country’s leading criminologists, concluded that, due to the inadequacy of the available research, “we can have very little confidence that improved lighting prevents crime.” At the time, this was certainly the correct conclusion. Most of the available evidence was very old — from the 1970s — and consisted of comparisons between a single treated community and some other community, whether it was comparable or not.
In the last 25 years, street lighting research, like other areas of social science, has been boosted by the “credibility revolution,” which has inspired empirical crime researchers to invest in obtaining stronger evidence. The lion’s share, albeit not all, of the more recent research finds that crime, including violent crime, declines in response to improved lighting. The crime declines that are observed have been modest but are large enough to be meaningful. On average, the crime reduction that we see in response to enhanced lighting is of an order of magnitude similar to that which would be expected from 10% more police. However, much remains unknown, and some additional findings remain more speculative. First, we have little understanding of the types of places where lighting interventions will be most successful. This means we can offer little formal guidance to policymakers about how different types of communities or places should be prioritized for enhanced lighting. The best advice, in my view, is simply to prioritize areas that suffer from the highest rates of outdoor nighttime crime and that, at present, have the lowest-quality lighting. There is some empirical backing for this advice as research on daylight saving time has found that the impacts are felt disproportionately in communities with less municipal lighting and those with higher crime rates.
Second, the mechanisms through which better lighting reduces crime remain murky. Does better street lighting reduce crime by bringing more people outside, increasing the number of eyes on the street? Or does lighting work mostly by deterring would-be offenders? If it is the latter, what is it about lighting that deters? Is it simply a matter of the increase in ambient light that increases the perception that there will be a witness to a crime or that the police will observe a crime in progress? Or does better lighting send a more abstract signal — that a particular area is looked after and cared for? In sorting out the potential mechanisms, we can engage in some informed speculation — informed because there is empirical research that sheds some light on these questions but still speculative because the available literature remains thin.
With respect to whether lighting will change the way public spaces are used, one recent study of daylight saving time found that, when there was more ambient lighting, more people were out and about at the same hour of the day than when it was darker. This suggests — but does not prove — that better municipal lighting might change the way public spaces are used. We will soon have more data to answer this question. The availability of cellphone mobility data from firms like Safegraph and Advan makes it possible for crime scholars to observe whether better lighting brings more people outdoors, thus generating more eyes on the street. The Philadelphia research, referenced in the prior section of this brief, will report such estimates in the near future. These findings are relevant to our understanding of public safety and important for other reasons. Outside of observed crime rates, the extent to which people are willing to use public spaces in their community after dark is an important measure of fear and well-being.
With respect to whether it is ambient lighting itself or the signaling effect that improved lighting might have, there is some tantalizing evidence that the signaling effect of lighting may play an important role in shaping the efficacy of lighting interventions. First, it is potentially noteworthy that one of the largest effects in the literature comes from the randomized trial in New York public housing that studied lighting that was very bright and especially salient to community residents. Second, in that study and several others, better lighting also appears to have led to some decreases in daytime crime. This is especially remarkable as streetlights do not turn on during the day, so there is no other way for street lighting to have an effect on daytime crimes except by sending a signal about community caretaking.
Finally, we can say something about whether lighting is reducing crime by leading to more incapacitation — and thus widening the net of the justice system. This is a plausible hypothesis about how lighting could work. With better lighting, surveillance footage might have greater evidentiary value, eyewitness testimony might be more useful, or police might directly observe a crime in commission. But two available data points suggest that lighting reduces crime without more arrests. Most notably, the randomized trial from New York that found outdoor nighttime crimes fell by 36% in response to enhanced lighting also found that arrests fell. Daylight saving research finds that street crimes decline but there is no indication that arrests fall with darkness. Likewise, while more research is needed to determine whether these findings will hold across a broader range of interventions, this finding is potentially very powerful: Interventions that reduce both crime and arrests represent the holy grail of public safety — and offer a double dividend to society by reducing victimization as well as the cost of adjudicating and punishing criminals.
One final caution merits discussion. Investments in physical infrastructure are often compared to investments in policing, with discussion ensuing about which effect is larger and therefore which is the wisest investment. Such discussions miss the mark and are based on a misleading read of the available research. To my knowledge, there has yet to be a paper that tests the effects of an intervention that increases lighting while reducing police presence at the same time. As such, lighting studies are probably best thought of as revealing the impact of improved lighting, holding law enforcement inputs constant. From a conceptual standpoint, police and community investments are considerably more likely to be complements than substitutes. Lighting makes places more defensible, but the most sustainable forms of safety are likely to be created using a layered approach.
