Sometimes just asking a question in a thread, and seeing one "response post," inspires me to dig further. First, and I should have put this in my OP, I am referring only to VLT ratio (visible light transmission), for there are often other window tint standards regarding reflectivity, etc.
So, re VLT, I just learned that most OEM's have a window tint of between 72 and 78, and the reason why it appears that no OEM has a lower than 70, is that that is the legal limit in some states.
Second, learned that to get a rough VLT percentage of how a window is tinted, you take the OEM tint, say 70 for ease of multiplying, and then if one were to choose a window film with a 20 VLT, you multiple the two (.7 X.2) to get a VLT of 14. As that method is very rough, the way many law enforcement and window tinting businesses measure actual VLT is by using a VLT meter.
Third, I just found a YouTube vid in which the person, with a meter in hand, said that Mazda uses 75 VLT window.
So putting all this together, to be legal in my state which requires a 35 on all side and rear windows, I would need to go with a film with a 47 VLT -- but of course no one makes that, and IMO a 50 VLT is not worth it to me (little change to the eye).
I live in a northern U.S. climate, so tint heat rejection is not my issue, but visual appearance and cutting some of the glare is what I am seeking. So I am going with a 35 tint, while technically illegal, probably resulting in around a net of 27 VLT.
However, I have learned one other major factor, that there a huge visual difference, even for the same VLT, on how dark is the vehicle's interior color, i.e., from the outside, windows with a 35 VLT with a black interior are going to look far darker than an identical car with a very light interior.
Pics next week.