Here is a link to the study in Encolplus' article. It doesn't sound like that's what they're talking about
:
https://jech.bmj.com/content/69/11/1...jech_ahead_tab
People who are complaining that crime rates might actually increase even if gross numbers decrease seem to be assuming that criminals aren't affected by the lack of lighting, whereas other citizens are. If 20% of non-criminals reduce their activities after the lights go out because they cannot see very well anymore, there's no reason to believe that criminals won't be similarly affected. Criminals have to see things to commit crimes, just as much as ordinary citizens have to see to walk their dogs.