How dark your tint can be depends on what is legal in your state. For example, here is what is legal in the state of Connecticut
Any vehicle with an after market tinted window must have a tint compliance sticker affixed to it by the Department of Motor Vehicles. Stickers may be affixed to vehicle windows which, when tested, have an allowable light transmittance of no less than 35 percent plus or minus three percent.
Rear Window: If the vehicle is equipped with left and right-hand side rear view mirrors, the tinting standard does not apply to the rear most window (back window).
MPV: If the manufacturer's certification label in the driver’s door jamb identifies the vehicle as an MPV, the windows to the rear of the operator may be tinted as dark as desired provided the vehicle is equipped with left and right side rear view mirrors. (This is where my Explorer would be categorized)
Trucks, motor buses, trailers, motor homes and livery vehicles: The windows to the rear of the operator may be tinted as dark as desired provided the vehicle is equipped with left and right side rear view mirrors.
Medical Exemption: If a medical condition exists which requires tint between 32 percent and not less than 20 percent, a medical exemption form must be completed.
Therefore, in my state, I can have any windows to the rear of me as dark as I want, but the driver and passenger doors and the windshield can't be more than 35 percent
Laddy, I would find out from your DMV what is the most you can have your Explorer tinted by your state's laws