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| The lower the VLT number, the less light the film lets through. This image demonstrates the different window tinting percentages ranging from 15%-50% |
A window films "darkness" is described through its visual light transmission (VLT) percentage. This is the percentage of light a window tint lets through compared to the amount of light that that falls on that surface. For instance, a 20% window tint allows 20% of the light to pass through, while blocking 80%, and a 35% allows 35% of the light to pass through while blocking 65%.
Here is the dictionary definition of VLT:
- visible light transmittance (VLT)
- The ratio of the amount of total visible solar energy (380-780 nanometers) that is allowed to pass through a glazing system to the amount of total visible solar energy falling on the glazing system. Value is usually expressed as a percent. Glare is influenced by visible light transmittance through a glazing system. Visible light accounts for about 44% of the sun's energy reaching Earth's surface. The VLT value is often weighted or measured in the area of the spectrum most easily sensed by the human eye, around 550nm.
As you can see, the lower the number, the "darker" the tint. Most window film manufacturers round off their percentages when naming a film. Your typical automotive window film that says it is a "35" can have an actual VLT percentage of more or less, but it is usually very close to the stated percentage.
As roughly 44% of the suns heat comes from visible light, the more light you block the more heat you reject. VLT is also an important factor in glare control. Keep in mind that some state window tinting laws are based on a "net" value VLT which is the combined light transmission of the window tint and the glass. Most glass which appears "clear" has an actual VLT of somewhere between 67%-89% so an appropriate window tint must be chosen to stay within the legal limits.
The VLT is one of the most important factors when considering a window film or tint. This will determine how much light you allow to enter the space and "how dark" the space will be. One of the most popular window tint percentages for home installation is a 35% as this percentage allows a respectable amount of light and can drastically reduce heat gain and glare.
Please leave us a comment below if you have any questions about window tinting, window films, or window tinting percentages.
