In one of the most comprehensive, statistically, and scientifically valid studies to date, temporary outdoor lights were found to reduce outdoor nighttime crime by 39 percent in the crimes that they indexed. (Download the study here).
The light installation reduced all crime including daytime and indoor crime by 7 percent.
They found that the LED light deployment reduced overall felonies, including daytime and nighttime including both indoor and outdoor crimes by 5 percent. Additionally, they found a 30% reduction in the felonies that took place at night. They also demonstrated a 12 percent reduction in assault, homicide and weapons crimes that took place outdoors at night.
While there have been other studies that examined the effects of lighting on crime, this study is the first randomized and controlled study to do so. The New York City Housing Authority (NYCHA) housing and Crime Lab New York (CLNY) partnered with the city of New York to design a randomized study about the effect of temporary outdoor lighting on crime in and around New York City Housing Authority developments in all five boroughs of the city.
Study Based on Dosage Model
They used a “dosage model” to examine the effectiveness of lighting. The model used a randomized allocation of the
number of light towers per development, creating a variety of treatment levels. Specifically, the test looked at whether developments that received a greater dosage of lighting showed larger reductions in crime. While dosage was intentionally varied from the start, the study also initially attempted a simple comparison of treatment and control sites.
In early 2016, CLNY randomized 39 areas into treatment and 38 into control sites. Among the treated developments areas, about four hundred light towers assigned to the treated developments where each development received a number of additional light towers.
The number of additional light towers was based on a randomly assigned dosage variable, chosen from a uniform distribution of lights per square feet. This research design allowed them to show that at a certain point adding lights effectiveness of lighting diminishes as more lights are added to a development.
They also performed a non-random survey to get feedback about the perception of the lights. For the survey, 67% of respondents had a favorable opinion toward the lights; only 13% of respondents had a negative opinion.