Ernest that is a great question about window tinting; all vehicles sold in he US have to pass strict DOT (Department Of Transportation) standards however each State can also have their own laws. Regarding window tinting the standard law states it is legal to tint all the windows except the front door glasses and windshield. In some States like Arizona and Hawaii it is legal to tint the front door glasses. To date the only vehicles sold in the US that have an option of dark tinted glass are SUV, trucks, vans and limousines, that glass is referred to as privacy tint. All other cars that are tinted have had an after market tint applied to the glass. After market tints come in grades from 5% to 70%; the percentage is the amount of ambient light that passes through the glass. So a 5% tint being the darkest allows 5% of the light to pass through. You also have to take into consideration the time of day and amount of light. At night tinted glass looks much darker. Some customers that have vehicles equipped with privacy tinted glass may require more security from prying eyes. In those circumstances you can also add an after market tint to the privacy tinted glass.
Hope this helps – Felix