From this perspective, by providing anonymity, darkness may facilitate dishonest behavior. When transgressors believe others will not be able to identify them, are they more likely to behave dishonestly? Scholarly work conducted in the 1960s and 1970s found that criminal assaults most frequently occur during hours of darkness and that improving street lighting in urban areas is commonly followed by reductions in crime of between 33 percent and 70 percent -- impressive gains. Although interesting, the sci­entist in me notes that this evidence is inconclusive, as the rela­tionship between darkness and crime suggested by this data could be explained by other factors. I wondered whether there is a direct relationship between darkness and crime rates. Even more inter­estingly, does darkness increase dishonesty?

Soon after Greg and I received our letter from City Hall, Chen-Bo Zhong (a professor at the University of Toronto), Vanessa Bohns (a professor at the University of Waterloo), and I designed a series of experiments to test whether darkness -- or even dim lighting -- would increase dishonesty.

Chen-Bo, Vanessa, and I tested this possibility by conducting an experiment where we manipulated darkness by varying the level of lighting in rooms. Upon arriving at our laboratory, our eighty-four student participants were randomly assigned to one of two rooms (with about half in each room): one of them was well lit (our control condition); the other one was similar in size but was dimly lit (specifically, lit by four fluorescent lights rather than by twelve). Participants in the dim room could see the materials and one another, but the room was more dimly lit than the aver­age room at a university. Participants completed a problem-solving task: they had five minutes to solve twenty problems (which involved finding two three-digit numbers that add up to ten in a matrix of twelve numbers), and were paid 50 cents for each problem they solved correctly. After the five minutes was up, participants in both conditions were asked to self-report their performance on the problem-solving task. They were able to lie by overstating their performance and thus walk away with undeserved money. As in other experiments concerning dishonesty, we tracked whether participants cheated and, if so, by how much. If you were a participant in this experiment, do you think you would cheat by overstating your performance?

Maybe you would stay true to your moral compass. But, as it turns out, many of our participants did not: in fact, on average, about half of them cheated across conditions. More interestingly, the level of darkness in the room dramatically influenced partici­pants' likelihood to lie by overreporting their performance: almost 61 percent of the participants in the dim room cheated, while "only" about 24 percent of participants in the well-lit room cheated. In other words, eight additional fluorescent lights reduced dishonesty by about 37 percent. This is quite a large difference, especially con­sidering that the task Chen-Bo, Vanessa, and I used in the experi­ment was completely anonymous: the only difference between the two rooms was the level of darkness.