How Are Window Tint Percentages Calculated?
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Car window tinting films are measured in visible light transmission levels (also known as VLT), and these levels are represented as a percentage of the visible light transmitted through the windows. So, when you see a window film being referred to as a percentage, this is the VLT. “Let’s do 35% on the back windows,” means 35% of the visible light will pass through the window film.
In the simplest terms, the lower the percentage, the darker the window film will be. A 5% VLT film is very dark as it only lets though 5% of visible light and a 70% film is very light as it lets through 70%. There is, however, one little complication, and that is that windows as installed by the factory do not allow 100% of light to pass through. Most auto makers very slightly tint their glass, usually with a VLT of about 80%.
So how do you calculate the true VLT of your windows?
To calculate the actual VLT of the glass with film applied to it, you need to multiply the VLT of the window tint applied by the VLT of the glass. For example, applying a 5% film to glass with an 80% tint to it, you would multiply 5% x 80% = (0.05×0.80)x100 = 4%. So the glass and window tint would have a combined VLT of 4%.
Is there a way to test my windows for their current VLT %?
As a matter of fact there is! Most installers will be able to tell you with one look and be correct within about 5%, that is because we do this all day, everyday, and you get to know your product pretty quickly. Law enforcement officials and many professionals might use a device to get a VLT reading that is extremely precise. Here is an example of one. You clip it on your window and it uses a laser to test the permeability of the window film. Its a cool piece of gear for petrol-heads, pros, and anyone super keen on the window tinting game.