hey, i think sunblock will do whatever percentage tint u want, 20 percent and even lower, but if its lower than 35% then they dont give u that sticker to certify its legal. also note that most car manufacturers already have some form of film on their windows, which will inturn the lower % even more. there are some places out there that put these legal stickers on there only to cop fines for illegally putting the 35% VLT sticker on when in fact the tint isnt what at the level of what it specifies.
note that for the front two windows (driver's & passenger) the legal limit is 70 percent i think it is...(which is pretty much clear window) with the rear & quarter windows being allowed the 35%
Hope that helps,