Actually, in California the two front doors' windows are allowed to have 70% VLT film applied. This is a standard that was set by IWFA (International Window Films Association) working in conjuction with states to come out with a legal standard for the films industry. However, the front windshield is a different story, it is not allowed at all in California.

I personally have 55% on the front windshield regardless just to protect the occupants and interior from harmful UV rays.