How dark can you tint your car's windows

Q: I'd like to get my Range Rover's windows tinted, but a friend told me there are laws about blocking out too much light. Is this true and, if so, what are the rules?
James Hewson

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.