Researchers evaluate the effect of improved street lighting on crime rates

It’s an almost universally accepted truth that walking in well-lit areas is safer. But Aaron Chalfin, associate professor of criminology in Penn’s School of Arts & Sciences; John MacDonald, criminology professor and director of the Master of Science in Criminology, and Brian Wade, senior data scientist at Penn’s Crime and Justice Policy Lab, want to know what this knowledge means on a society level: Could improving vast swaths of a city’s lighting enhance public safety by acting as a significant deterrent to crime?

“A number of studies suggest that enhanced streetlights reduce crime, but we have never seen an evaluation of a citywide initiative,” says MacDonald.

“Discovering that the City of Philadelphia was planning to roll out an upgrade of its lighting system led us to think this was a unique opportunity to see if enhanced lighting could lead to public safety benefits at a large scale.”

In a two-year study that began in August 2023, they found that by upgrading tens of thousands of streetlights to LED fixtures that increased both the volume and clarity of lighting, outdoor street crime at night declined by 15%. This includes a 21% drop in outdoor nighttime gun violence in the affected neighborhoods during the 10-month period in which the upgrades occurred, amounting to 5% of the citywide drop.

The streetlight research came on the heels of another study that Wade and MacDonald had conducted about litter cleanup’s effect on gun violence.

“We had engaged with the community on how these environmental interventions can shape safety, social cohesion, and the way that people use public spaces—all of which are critical for reducing crime and violence more broadly,” says Wade, who manages much of the Crime and Justice Policy Lab’s qualitative research portfolio.

“The idea was to get a feel for the vibe of how the neighborhood looked at night, right before sunset, before the streetlights really turned on. Were people out and about using public spaces? Were businesses open?” says Wade, whose current research examines community gun violence, neighborhood safety, and violence reduction interventions.

“And then, once the streetlights turned on and the neighborhood was fully dark, did people stay outside? Did they continue to have social interactions at night?”

Then the team conducted a series of focus groups facilitated through a partnership with the Urban Affairs Coalition, a home for nonprofits who work to improve the quality of life in the Greater Philadelphia region. Residents from the relevant ZIP codes came in to discuss neighborhood conditions.

This feedback helped inform the quantitative analysis, and it suggested potential mechanisms by which enhanced streetlights improve public safety. “By hearing from their insights, we got a better sense of what is actually happening in neighborhoods,” says MacDonald.

Wade says one of the more surprising findings was that many of the residents from neighborhoods studied had self-imposed curfews to avoid being out too late or they intentionally stayed away from certain blocks with poor lighting conditions.

“It becomes this pattern of people very much associating times of night, darkness, and a lack of people on the street with feeling vulnerable to crime,” says Wade.

Several business owners in the focus groups also suggested their establishments were not thriving at night in the same way as businesses in other parts of Philadelphia—South Street, for example, says Wade—where restaurants and other commercial fronts are open late into the night. Nighttime violence has also led to finger pointing at certain types of stores, such as smoke shops and liquor stores.

In the future, the researchers would like to explore a collaboration with law enforcement, given that streetlights could potentially improve aspects of police work like evidence collection and surveillance.

“These findings offer some optimism for the public safety benefits on improving infrastructure in cities like Philadelphia,” says MacDonald.

“The public safety benefits of upgraded streetlights are a complement to energy savings, and the residents we spoke with viewed upgraded streetlights as a positive sign of city investment.”