I just ran into this story on a Arizona news site. (I am in AZ)
It talks about a LEGAL (at least in Arizona) clear windshield tinting.
"The untreated window was off the chart. The traditionally tinted window registered more than 300 BTUs. The window with the clear tint came in at just over 100 BTUs.
Hernandez said the clear tint blocks 99 percent of the UV rays and 43 percent of the heat"
"The clear tint goes on the inside of the windshield and runs between $200 and $250."
Check out the article.
New clear window tint designed for windshields | azfamily.com Phoenix
I am totally going to look into this for my Mustang (black cars + Arizona summers = One HOT Pony)
(I have standard 'dark' tint on all the other windows)