Do you have a source for this? I've always been under the commonly held impression that this has a preventative effect, and it would be very interesting if the opposite really is true.
UPDATE: Hey, awesome, turns out we blogged about it back in the day: http://blog.ratemystudentrental.com/2008/03/05/a-safe-home-i...
Here is the original article: http://www.schneier.com/blog/archives/2007/09/light_and_crim...
Much so-called security lighting is designed with little thought for how eyes -- or criminals -- operate. Marcus Felson, a professor at the School of Criminal Justice at Rutgers University, has concluded that lighting is effective in preventing crime mainly if it enables people to notice criminal activity as it's taking place, and if it doesn't help criminals to see what they're doing. Bright, unshielded floodlights -- one of the most common types of outdoor security lighting in the country -- often fail on both counts, as do all-night lights installed on isolated structures or on parts of buildings that can't be observed by passersby (such as back doors). A burglar who is forced to use a flashlight, or whose movement triggers a security light controlled by an infrared motion sensor, is much more likely to be spotted than one whose presence is masked by the blinding glare of a poorly placed metal halide "wall pack." In the early seventies, the public-school system in San Antonio, Texas, began leaving many of its school buildings, parking lots, and other property dark at night and found that the no-lights policy not only reduced energy costs but also dramatically cut vandalism.
I remembered it incorrectly, as apparently motion-activated lighting helps, but on-all-night floodlighting makes the situation worse.
In short, sometimes darkness helps. Consider a tall glass office building. If all the lights are out, nothing stands out to a security guard more than a flashlight waving around in the darkness.