Mine are supposedly 20% light transmission so block 80% of the light from coming in and is described as 'light smoke' in a kit I bought on eBay.
Limo tint is around 15% transmission and you can get ultra dark tint if you feel the need.
The reason I went for a light tint was because in the UK you can't tint the front windows so I wanted to minimise the difference when looking at the car from the side
On my Megane my side windows had a slight tint and the back side and rear was slightly darker and never had a problem with the police,Even got pulled over once for something silly and they said nothing about the fronts