Window film manufacturers and installers use a measurement called the Visible Light Transmission (VLT) to gauge the darkness of a window tint. The VLT of a specific tint is given as a percentage of the visible light that passes through the window. A tint with a VLT level of 50% means that 50% of the visible light that a window is exposed to will pass through. The lower the VLT percentage, the darker the window. A 5% VLT tint is very dark, as only 5% of exposed light passes through, whereas a film rated 70% VLT is comparatively light.
Note: VLT only refers to visual light and does not effect the ultraviolet or infrared (heat) blocking qualities of window film. In fact, even our highest VLT films still block 99% of UV and more than 80% of infrared.