Nighttime lighting reduces crime but it's not a one-size-fits all solution, study shows

A mobile lighting unit is set up at a public housing complex in the Bronx in 2016.

(CNN)A recent study showed nighttime lighting in New York City public housing complex courtyards could reduce crime, and the reduction in crime held over the three-year period of the study.

Though the lighting appeared to reduce crime at the experiment sites in New York, the researchers and other experts cautioned against drawing too firm a conclusion about lighting as an anti-crime measure that can be used everywhere.
      "It seems to have worked beautifully in New York public housing, it could be applicable in others, but it's hard to make any firm claim about it," said Aaron J. Chalfin, one of the study's authors and a professor at the University of Pennsylvania. "If you look back at all the literature on lighting -- most finds effects (from lighting), but not all of it finds effects. It's one strategy city planners can use in conjunction with other things they can be doing. It's not magic that always works in all circumstances."
        Researchers studied crime in areas where the city placed temporary light stations -- the type typically used to illuminate construction sites. The emitted brightness from those fixtures was brighter than the lights used at Yankee Stadium. The experiment was conducted with the city of New York under the administration of former Mayor Bill de Blasio. Officials from the New York City's mayor's office didn't respond to a request for comment.

          Lights brighter than Yankee Stadium

          The fixtures gave off "600,000 lumens," while street lights are often between about 5,000 and 35,000 lumens and the brightest light at Yankee Stadium is 150,000 lumens, according to the study and experts.
          "This is kind of weaponizing light and using it in an experiment ... (you can use) space, light, other facilities to create a safe environment, that's the essence of crime prevention through environmental design ethos. This is the antitheses of that. You need quality lighting, quality lighting will make it safer, enhance the ability to see and to safely navigate space," Ruskin Hartley, executive director of the International Dark-Sky Association. The group advocates against light pollution to protect night skies while also providing resources to city planners and managers to help them use lighting in a responsible way.
          "If you're driving down the highway and high beams hit you and you have to look away, that's what's happening here. Those old police movies where they're interrogating a suspect and shine light directly at the eyes so they can't see, that's what's happening here."
          Other research showed lighting an area pushed crime elsewhere -- "displacement" of crime, Chalfin said. In the New York study, the circumstances didn't really allow for that and the data showed the crime wasn't displaced. Part of that was because people are so closely tied to their communities in the densely populated city -- "moored very tightly to areas where they live."
          "More lighting can equal less crime when done in a way that understands context. You put these big mobile light towers in, they're really alien, really bright, people can't easily hang out in other areas ... If you can find context like that, I think (lighting) is a decent bet."
          In this study, the lights were installed in 2016 and left in place for three years, allowing researchers to amass data over time and from among 40 sites where lighting was installed and 40 sites where lighting was not installed. The study is in review now, but is an update to a study previously published in the Journal of Quantitative Criminology with six months of data, and was the first randomized experiment that studied the effect of lighting on public safety, according to the researchers. This paper draws on three years of data.

          'These areas are being cared for'

          The light units assigned to public housing courtyards were the type used by construction crews for temporary lighting and were powered by diesel.
          "It's not regular street lighting. It's a very specific kind of intervention. At the same time it can be scalable, very common to have this type of equipment," said David Mitre Becerill, another of the study's authors. "It's not just regular street lighting you'll see in every street."
          Over the three years, researchers estimated overall nighttime index crime dropped by 45%. Chalfin said that the main crimes in this category were assaults and robberies -- crimes serious enough that they could escalate into something where detectives might seek to pull video. Less serious crimes, less likely to get serious investigation (like urinating in public) dropped but not in a way that was statistically significant.
          The study also showed some reduction in daytime crime -- something Chalfin attributes to a "signaling effect" of letting people know the area is watched and cared for.
          "These lights signaling something, that these areas are being cared for, watched ... it leverages better ambient lighting but also doubles down on the demonstration, signaling effect," he said.
          Art Hushen, president of the National Institute of Crime Prevention, said lighting can deter crime but it also can generate "positive social interaction." But the lights in this study are many times brighter than the lights at Yankee Stadium, Hushen said. His company trains police and other government officials on crime prevention through environmental design.
          "We forget that good lighting can bring people to a space, help them take ownership of it, use it, the police don't have to be there, and the space is luminated and you can notify police if they're needed," Hushen said.
          "Neighborhood lights are 5,000 (lumens), flashlights are 250, 300. Those are still bright, blinding in your face, that's 250 lumens. Six-hundred thousand, that's like hundreds of those flashlights turning on your face at the same time."

          'Mixed views' on brighter lights

          Lighting itself can have negative effects on health and on quality of life, and it's not simple enough a scenario to say that more and brighter lights will lead to decreasing crime. And one resident, early in the research, told Chalfin the courtyard looked like a "concentration camp" because of how it was lit.
          "The lights are a little ugly, you might not want one on your block. There are mixed views," Chalfin said. "But the survey work the city did, among people who responded to the survey, three quarters of the people were happy with the lights."
            The study gives policy makers data to support lighting as a crime-prevention measure, but it's at odds with what lighting experts consider to be best practices for lighting. Hushen also wondered whether people who supported the lights were those nearest their location, or if they were perhaps on the other sides of buildings or higher up and benefited from the light without having to deal with the sound or sight of them in their apartment. And though scientists studied the lighting intervention, policymakers have to decide what to do with the data.
            "The electeds are like, 'I got my apple for the day, we did it, we dropped crime.' But can you imagine living there? That would not happen in an affluent neighborhood. Would not happen if people were paying a lot for those apartment complexes," Hushen said.