I live in Phoenix, AZ, so I know about heat!!!
It's going it be 110 degrees F, today. (43.3 C for Europe, Middle East, Asia and Australia, or 316.4833 Kelvin for our truly nerdy coharts). I don't have tinted windows, yet. My car definately feels hotter that my truck that has dark tinted windows. In the summer, the A/C is pretty much cranked up all summer long.
I know it seems that the dark would make it hotter, but it doesn't. The tint actually prevents some of the UV from coming in, thus keeping it cooler. What I am also considering is a film that is clear, but keeps out 95% of the UV. A lot of cop cars here have it and it is supposed to work well. Limo tint is only legal in the back windows. I was quoted about $200 USD a while back for it.
The rule of thumb that the police in Phoenix use for the drivers window is that if they can read your licsense through the glass and tint, then you are good.
I see tons of vehicles here, though, that are completely blacked out and you can't tell who is in there. Imagine being a cop on a traffic stop, especially at night, and trying to tell what you are dealing with. What a nightmare!!
They are pretty forgiving here because they understand the effect of the heat (seatbelt buckles or steering wheels so hot they burn you), but take your Arizona car up a few states and their such a-holes about it.
JD