What Car? Q&A - How dark can you tint your car's windows
A: There are rules regarding the level of tinting that can be applied to a car's windows.
For vehicles first used on or after April 1, 1985, the front windscreen must allow at least 75% of light to be transmitted through the glass, and 70% for the front side windows. The rear side and back windows can be tinted to any level.
If you have a car with excessively tinted windows, it should not be driven, because your insurance will probably be invalid. It is also an offence to sell a vehicle with excessively tinted windows.