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Understanding Window Tint Visible Light Transmission

Whether for a vehicle, home or commercial application when referring to window tint film, one of the most important characteristics is how much light the tint allows to pass through. In most applications, this is important when attempting to gauge how much security, privacy and protection from heat and harmful UV rays a tint offers. In automotive applications, however it is especially critical as a number of states have laws limiting how dark the tint can be on a vehicle’s windows. As a result, window tinting manufacturers have created a method for calculating how much light a tint allows to pass through it. However, there are a few things to consider when discussing the darkness of a window tint.

Regardless of the application, all window tint film is measured by the materials visible light transmission levels (VLT). Simply put, the VLT value is the percentage of visible light the tint allows through from the exterior of a vehicle, building or home to the interior. The lower the VLT percentage, the darker the tint is and the more outside light it blocks. A tint that has a VLT value of 5% indicates that the window film only permits 5% of the exterior light to pass through it, while a film with a 50% VLT value allows 50% of the light from outside to pass through. In addition, because tints are also offered in a variety of colors when professionals are referring to a tint they typically identify it by the tint’s color and VLT value. For example, a charcoal colored tint with a VLT of 5% is known as charcoal 5%. Likewise, a green colored tint film with a VLT of 50% is called green 50%.

While many might assume that the VLT of a tint is the only factor to consider when calculating the final VLT of installed window tint, there is one additional aspect that must be considered. Every piece of glass, regardless of the application, blocks a certain amount of light. As a result, glass also has its own VLT value, which must be accounted for in order to determine the installed tint’s final VLT value. For example, if a state law indicated that the lowest legal VLT value for a tinted car window was 30% and an individual were to install a tint with a 30% VLT rating, the windows final VLT rating would actually fall below the legal limit because of the window’s natural VLT value. Because of this, Window Tinting professionals use a simple formula to calculate the installed window tint’s final VLT value:

V1 (VLT value of glass) x V2 (VLT value of tint) = V3 (final VLT value)

Let’s assume, for example, the legal limit for the window tint of a vehicle is 30% and the vehicles glass has a VLT value of 75%. In this case, since we already know the VLT value of the window and the final VLT value we want to achieve we simply need to rearrange the formula to calculate the proper tint to install as follows:

V3 (final VLT value) ÷ V1 (VLT of glass) = V2(VLT value of tint)

0.30 (30%) ÷ 0.75 (75%) =.40 (40%)

According to this formula, installing a Window Tinting with a VLT value of 40% will result in a final VLT value of 30% as desired. Professional installers using this formula save their customers a significant amount of money not only in traffic tickets for illegally tinted windows, but also in the reinstallation of window tint which most traffic courts require when a driver receives a ticket for illegally tinted windows.