Tinting of windows can be done for cosmetic
reasons but also to reduce the heat in the car in the summer.
However, reversing with heavily tinted windows, especially in the dark, can be
difficult as visibiliy is less.
Rear facing extra lights is a good compliment.
The following restrictions apply in Sweden.
Windscreen:
In the area of sight (as officially defined)
75% of light must be let through.
You can however have a tint across the top of the windscreen.
Front side windows:
In the area of sight (as officially defined) 70% of light must be let through.
Other side windows and rear window:
No restrictions.