We have many come in to have their two front doors done to match
their factory tint that came with it on the back part and while they are
here, they ask if we can darken up the back part as well. Of coarse we
can as long as it is factory pigment within the glass itself and not
film on the surface.
While it can physically can be done, you shouldn't double layer films
because it voids warranties and kills life spans of both layers of film,
but if it's true factory tint (which is mostly what we see here) then
it's no problem at all and legal as well (here in Texas) and many would like it a bit darker. You just have to be careful as to how
much darker you make it so you don't have night vision problems.
We usually recommend using a 35% on top of the factory tint in most
cases. This will make it a bit darker and bring it to about the same
compared darkness as our 5% installed on clear glass.
Going to the next level of darkness by putting a 15% on there will
make it crazy dark and you better really want to live with that such as
for using to watch solar eclipses and such, because you'll be using your
outside mirrors only for night time backing........... Vision is not bad
during the daylight hours, but at night, most will find that once the
new wears off in this scenario, it's not such a great thing unless your
used to driving a cargo van with no windows in the rear part of
it.......
