Meaning, definition of VLT and how to calculate VLT on window tinting

VLT (Visible Light Transmission) is very common term in solar window films, automotive as well as building windows

VLT levels are represented as a percentage of the visible light transmitted through the window. So, when you see a window film being referred to as a percentage, this is VLT
Or the VLT is the percentage of light that the film allows to pass through. So a 5% VLT film is very dark as it only lets though 5% visible light and a 70% film is very light as it lets through 70%

Most of the automotive glass usually contains some level of factory tinting, range of 70% to 85% light transmission. Net VLT means both factory tint on the glass and the dark of film and not the just film alone.

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. E.g 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%.