Most states post their regulations regarding the percentage of tint you can have. Here is what I found for the state of Alabama:
Window Tint Law
All vehicles registered in the state of Alabama must comply
with Alabama window tint law, Act 96-534, which was
effective August 15, 1996
Only the upper six inches of the front windshield may be tinted. All other windows
may have tinting that allows as least 32 percent light transmission, with a 3 percent tolerance for error. Reflective material may not reflect more than 20 percent of light.