Terminology
What is VLT?
VLT — visible light transmission — is the percentage of visible light that passes through the glass and film assembly. It governs how bright the space feels and how much glare is reduced. Lower VLT means more glare control and less daylight.
VLT is the number to argue about when the complaint is glare, because glare is a visible-light phenomenon. It is not the number that governs heat rejection, which is a common source of confusion in specifications.
Values are always for the assembly, not the film alone. The same film on clear glass and on already-tinted glass produces two different VLT figures.
In practice the design question is how low you can go before the space feels gloomy on an overcast winter morning — which is a use question, not a product question.
Technical performance, service life and warranty terms come from current 3M documentation for the specific product and application. We attach those documents to proposals rather than paraphrase them.