"I just can't leave a world that invented The Smurfs."
There are several theories. First, there's the fact that science has observed for decades that blue is a calming color, as opposed to such "Let's raid shit!" colors such as yellow or red. But there's also another theory, which is that blue is the universal color of "Holy shit! Cops!" and the blanket of blue keeps people on their best behavior because they subconsciously feel that they might be busted by the cheese at any time. Others say just the fact that there was a change at all may have made criminals uneasy -- the fact that the lights had been installed implied that somebody was paying attention.
Either way, it appears that the illusion that Big Blue Brother is watching you at all times is subconsciously enough to keep you honest and law-abiding. And all because of Officer Light Bulb.
You'll make sergeant for this!
And while we're on the subject of seemingly insane law enforcement strategies ...