What is the full range of transition for the 25%, as far as volume of light - what is the lightest to darkest range for this film?

Here is the spec sheet for this product. If will show you the ranges. https://www.decorativefilm.com/mm5/graphics/00000001/UltraCool-IR8025T.pdf We also have a film with a much wider range of values. See it here. https://www.decorativefilm.com/ultracool-ir8675t-75-30-vlt-transitional-ir-solar-film