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Streetlights and citizen safety

Updated: Jul 22, 2019

Is it all just an illusion?

Madrid and its sky glow
Madrid and its sky glow. Photographer Alejandro Sanchez de Miguel.

During most of the course of human history ´artificial´ light at night meant fire. Fire kept us warm and safe from predators and on top of that, it cooked our food. The positive associations that people have with light at night therefore make sense.

But is this sense of safety still appropriate in the age of electricity and with most of our natural predators close to extinction?

There are two popular beliefs when it comes to streetlights; the first is that plenty of streetlights make the streets safer for citizens to be out at night. And the second is that plenty of streetlights will decrease the amount of traffic accidents at night. The belief that citizens are safer with more lights has become so popular that, internationally, authorities are advising citizens to increase outdoor lighting in order to protect themselves from possible crimes.

The evidence

Surprisingly though, very little scientific evidence supports these beliefs. And this has led to scientists raising the alarm. Mainly, because many new studies are identifying streetlights as a major threat to the survival of a large variety of animal species including bees, bats and migrating birds. Furthermore, new research suggests that certain types of streetlights interfere with our hormones and are causing an increase in breast and prostate cancer in humans.


People have been using lights to illuminate the streets as early as the 16th century. But it was not until the beginning of the 19th century that invested companies began to push for massive installation of gas street lights. Aside from streetlights being a lucrative business, one of the reasons mass-wide use of gas streetlights became popular was due to the belief that light reduced crime in the streets. Journalist, and Chief Public Relations Officer of the Madrid Municipal Police, Antonio J. Gomez Montejano believes that the reduction in crime during the time of gas lamps may indeed have been correlated to the presence of streetlights. But not in the way one would expect; he explains in his book Las doce en punto y sereno (1997) how gas lights needed frequent maintenance which meant that each lit streetlight had two maintenance people in the nearby facility. And it may have actually been the presence of these maintenance people that led to a reduction in crime.

The research

As the case of the maintenance people demonstrates; correlation does not imply causation. Criminologist Ken Pease observed that studies performed during the 1980s up until the mid 1990s assumed without evidence that light reduced crime, as if by magic. He points out that no effort was made to find out the mechanisms at play whenever a correlation between an increase of streetlights and a reduction in crime was found. And when Pease conducted a review of several of those studies he found no evidence that an increase of light was directly responsible for the reduction in crime rates. In some cases the crime rates had indeed gone down as the lights had increased. But interestingly the reduction in crime was both at night as well as during the day. The study in question offers no explanation for this phenomenon. Furthermore, one of the studies Pease reviewed seemed to imply violence had increased as the area had gone brighter.

Another example of why the relationship between streetlights and crime needs to be properly examined is the case of Berlin. The city of Berlin has the largest collection of gas lamps in the world illuminating the streets of the Steglitz-Zehlendorf district. Possibly, these living fossils are the dimmest streetlights currently used in the western world. Interestingly, according to the Berlin authorities, this dimly lit district equipped with gas lamps does not produce more crime than areas lit with lights of a higher intensity.

Paul Marchant, a statistician at Leeds Metropolitan University warns that many studies, claiming outdoor lighting is beneficial for citizen safety, contain major statistical errors. According to Marchant, some study results could even indicate the opposite; that brighter outdoor lighting leads to less safety for citizens. One theory, as to why that could be, proposes that more light makes potential victims more visible to perpetrators. Meanwhile, criminology surveys indicate that most criminals do not identify lighting conditions as an important factor when deciding to commit a crime or not. Much more important is the presence of video surveillance cameras or how doors and windows have been secured.

Clearly many factors can play a part when a suburb experiences a reduction in crime. It is not uncommon for a district or suburb to undergo a general upgrade that includes not only new streetlights. For example, the Lavapiés suburb of Madrid had its lighting increased as well as its pavements expanded, making it possible for commerce to place terraces outside which led to more people interacting in the streets. Again, one could derive from this that it is the increased presence of people, and not the increased lights that caused a drop in crime rates.

The ever growing amount of streetlights has changed our environment drastically compared to what it looked like forty years ago. Disturbingly, all this is being done without having reliable data proving the benefits. Even more worrying is that it is being done without understanding properly how it is impacting the environment. And meanwhile, as the world shines brighter with each day passing, scientific evidence showing the negative impact on human health and our ever so important ecosystem is steadily growing.

Why is the research going at such a slow pace when the streetlight population is growing so rapidly? To answer that question we need to examine who is funding and publishing the necessary studies. Currently the majority of research into artificial lights at night is being funded by manufacturers of lights, governments and municipalities. In addition, a small part of the research is done by academics.

The research published by governments and municipalities is generally not peer reviewed; which means that statistical errors may have led to wrongful conclusions. Furthermore, governments and municipalities are often ordering the studies after the streetlights have been purchased and installed; which means that they want the study results to show that their expenditures can be justified with positive results such as; a reduction in crime due to newly installed streetlights. At this point it is worth mentioning that installing a single new streetlight carries an average cost of €4000. So that is a substantial amount of money that needs justification.

Research funded by manufacturers in the industry neither tends to be peer reviewed. And seeing as they are manufacturers of lights, they have an obvious conflict of interest as they would like to sell as many lights as possible; which means there is a great likelihood of publication bias. Not only are manufacturers selective in what they might publish, they are known to emphasise results that will increase profits. They do this by joining committees, conferences and special events where they promote unreliable success stories while ignoring vital environmental issues.

Academics are responsible for a relatively small percentage of studies being done as they do not have the funding to do more. Criminologist, biologist, statisticians and astronomers are a few examples of academics who are actively researching the topic. And like Paul Marchant points out; although there may sometimes be flaws in their studies, their work is peer reviewed, and often re-analysed. This method means that over time academics correct each other´s work making the results verified and as reliable as possible.


But while academics manage to slowly gather more evidence indicating that we should limit the amount of artificial light at night, one would expect governments to regulate the amount of light in our streets until more is known about its impact. Unfortunately though many governments are using recommended illumination standards, set by manufacturers in the industry, as their guidelines. And recently the EU has harshly criticised these standards implying that the recommended light intensity in the streets is highly exaggerated.

Regardless of the lack of evidence, it is a reality that many people feel safer in brighter streets. But how many birds, bees and turtles are we willing to sacrifice to live in a possible illusion? And are we willing to expose our children, our families and neighbours to unnecessary health problems caused by our desire to eliminate the darkness. As science uncovers more uncomfortable facts about that light outside our window we need to start asking ourselves these important questions.


Authors: Emma R. Howard in collaboration with Alejandro Sanchez de Miguel


Relevant links

Steinbach, R., Perkins, C., Tompson, L., Johnson, S., Armstrong, B., Green, J., ... & Edwards, P. (2015). The effect of reduced street lighting on road casualties and crime in England and Wales: controlled interrupted time series analysis. J Epidemiol Community Health,69(11), 1118-1124. Why Lighting Claims Might Well Be Wrong by Paul R Marchant

Have new street lighting schemes reduced crime in London?

Bright lights do not deter criminals, The Guardian

A review of street lighting evaluations: crime reduction effects by Ken Pease 1999

Outdoor Lighting and Crime, Part 1: Little or No Benefit by Barry Clark

A guide to the green public procurement of road lighting December 2018

The Conversation

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