How to calculate the transparency of the visible light window (VLT)

Window tints are measured at visible light transmission levels (or VLT). This means that when we discuss a particular movie, it is suitable for a car or any other application, we usually refer to it with its VLT value. VLT is measured in percent (%), so if you hear that the tint is referred to as a percentage, it is the VLT that determines this percentage.

For example, a dubbing film, called charcoal 5%, is a charcoal colored shade with a VLT of 5%, and a film called green 50% is a green colored colored film with a VLT of 50%. But what does this number really mean?

Well, in simple terms, the VLT value is the percentage of visible light that will be transmitted through the window tinting film from the outside of the film to the inside. This means that the 5% film will transmit only 5% of the light, and the 70% film will transmit 70% of the light. In essence, this means that lower VLT films will appear darker. For example, it’s usually 5% shades that we’ll see in limousines for privacy.

Thus, adjusting the 5% tint to the window will allow 5% of the light to pass through the glass from the outside to the inside, right? NO! Because we have to take into account the actual VLT window before the shade is even set. There is no such thing as a piece of glass, no matter how clear, with a 100% VLT. This is because glass naturally filters out some visible light.

Let's look at the tinting of the car window, since this is one of the areas where we often talk about the VLT due to the fact that in many countries there are laws that limit the tinting of dark car windows. Most modern cars come from the factory with windows reading the VLT somewhere between 72% and 78%, depending on the manufacturer, model and country. Let's say our sample windows are 72% readable, and we add 50% window tint film, what is the new and latest VLT of our car windows after installation?

The sum is very simple: V1 x V2 = V3 (where V1 is the original VLT glass before tinting, V2 is the VLT window tinting film, and V3 is the final VLT value for coated glass).

The windows of our cars are original VLT = 72% and hue = 50%, thus, V1 = 72 and V2 = 50

The sum is 72 x 0.50, which gives us 36, which we express as a percentage. Thus, a window with an original VLT of 72% will have a VLT of 36% after applying a 50% film.