Tint on car-windows

Anyone with authentic information about laws regarding tinting car windows? I have heard varying information, some say rear screen can be 50% and other fixed 25%, others say no tint allowed. Also I heard there are cases where people have a document permit allowing all tints, how and where to get that?
Question specifically for Karachi roads/laws.

Re: Tint on car-windows

If you have money you can gift wrap your car in tint otherwise in the current security problems even the removable sun protectors are challan worthy. Laws are ultimately irrelevant, it depends on the mood of your traffic police man.