If a light is out anywhere one the car, it counts, (e.g. brake lights, tail lights, fog lights, etc.)
Motorcycles have to have a light out in order to count.
If you see a car that has one of it's lights obviously broken, but they aren't on, that still counts.
If one light is way dimmer than the one on the other side, that counts too.
Also, if you're with people that are playing and you're not playing, then you're a bitch.