Do streetlights reduce crime?
A study of streetlight outages in Chicago in 2010-2018 found that outages caused 6-7% increases in robberies and motor vehicle thefts in the nearby neighborhoods.
In 2016, unusually bright light towers were randomly placed near public housing developments around New York City. Two studies, one looking at the first six months after the experiment and one looking at a period of three years, compared crime in places with and without the new lights and found that serious outdoor crimes significantly decreased in areas with lights. There was also a slight decrease in minor quality of life" crimes. The researchers concluded that the lights were properly preventing crime, not displacing it to other areas. However, the study failed to distinguish whether the impact was due to the lights themselves, or the "noisy, stinky" diesel generators powering them, which is especially notable considering that the study found nearly the same impact of the towers during daytime.
A 2008 meta-analysis of studies concluded that improved street lighting reduced crime by 21% on average. However, these studies had major methodological limitations.
Several studies have also concluded that Daylight Savings Time (DST) reduces evening crime. A study of the United States found that robberies decrease by 7% during DST, and similar or larger crime reductions were found by studies of Brazil, Uruguay and Chile. This literature can be taken to suggest that brighter environmental lighting, even if provided by streetlight improvements rather than DST, reduces crime.