My 2000 540i is set up so the highbeams run at a reduced output when the headlights are off. It's called Daytime Running Lights (DRLs). Can someone explain the functional difference between these and the "City Lights" that a few folks have installed? I realize that city lights use an additional bulb. But I don't understand the functional difference between them. In both cases, the high beam unit glows at reduced output when the headlights are not on. Right?