Doesn't work when the high beams are on and tailgating you for going "only" 10 MPH over the speed limit. Also many newer cars are coming out with "auto dimming" mirrors without the switch but that don't quite seem to cut out as much light. The problem isn't just with lights either, it's with a lot of different features including mirrors that can't adequately capture blind spots and bumpers that cause more harm due to mismatched heights. The differences in vehicles sizes overall probably lead to quite a few avoidable traffic fatalities and accidents.