For those that may be interested.
The Crown factory pigment tests out to 80% on the front side windows and 79% on the back sides. Those numbers along with manufacturer's tint film spec numbers and the formula below, should help get you close to choosing a tint that gets as dark as possible and still falls within your State's limits (if you care).
Many states have a maximum darkness that windows can be. It may be the same front and back or different. Both states and tint manufacturers use the darkness rating given in VLT (Visible Light Transmission). It's how much light from the outside is let in. A 90% tint is not dark, it's opposite normal thought. A tint with a VLT of 90% is very light because it allows 90% of the outside light through the window. A tint with a VLT of 5% is dark because it only allows 5% of the light into the car.
If tinting and attempting to stay within a State's laws, two tints must be factored. The darkness of the tint film to be applied AND the tint pigment already in the car glass from factory. For example, if a State's law says 35% is the maximum, a 35% tint film applied will not be legal (if you care) because combined with the tint pigment already in the window it will result in a final tint darker than 35%. Most sedans have a factory pigment tint of between 70% and 80% to abide by Federal Highway Standards. A 35% film applied to a car with 80% pigment will result in a final 28% VLT (Percentage math formula .35x.80x100=28 ). To meet a State's 35% max, for example, a tint with a 44% VLT would need to be applied to a car with 80% pigment (.44x.80x100=35). A little leeway is given in the popular tint tester most inspection stations and law enforcement use. It has a 2% +/-. So a tested window with a final 33% tint falls within the +/-2% of 35% if that's your State's limit.
Most quality tint manufacturers make tint in 5%, 20%, 35%, 50%. Some make 40% as well. However, these are standard ratings and may not be the actual value. Quality manufacturers will test their tint and have spec sheets of their actual ratings. For example, a tint manufacturer may market a tint as 40% but it really tests out to 43%. Or they may market a 35% but it really tests out to a 33%. These small amounts can make a difference if you are trying to get as dark as possible and stay within the law of your state and not fail annual inspections or get pulled over (again if you care).
A good tint shop should work all this out for you as well. But many shops are loyal to and only carry one particular tint brand, and it's possible their particular brand may not give you the exact percentages you are looking for.
Just info for those that like info.
