(4) Tinting material that has a lower light transmittance or
produces a lower total light transmittance than permitted in
subsection (2)(a) and (c) of this section may be applied to all
windows of a multipurpose passenger vehicle that are behind the
driver. This subsection applies only to vehicles that are
equipped with rearview mirrors on each side of the vehicle. The
windows as tinted shall meet the requirements for AS-3 glazing
material established by 49 C.F.R. Ư571.205 (1993) and the
American National Standards Institute standards incorporated by
reference in that federal regulation. For purposes of this
subsection, a ' multipurpose passenger vehicle' is a motor
vehicle with motive power that is designed to carry 10 or fewer
persons and is constructed either on a truck chassis or with
special features for occasional off-road operation.
You can find the whole thing here, I found what I needed to find. It seems that if the window is behind the driver it can be as dark as you'd like.
Relating to vehicle window tinting; creating new provisions; and amending ORS 815.040 and 815.220.