What would the SPF (sun protection factor) be for window film, using the same scale used by the sun screen manufacturers?
Since an SPF 15 allows you to stay in the sun without burning fifteen times longer than you could if you didn't use any sunscreen, the calculation, it would seem, of the SPF for window films would be fairly easy, and the numbers would be very large indeed. If the film product allows less than 1% UV transmission, the SPF would be about 100 or more. With 1.5% UV transmission, the SPF would be 66.66. With a UV transmission of 2%, the SPF would be 50. A film with a 99.9% UV block would have an SPF of 1000 or more. Simply divide 100 by the percentage of UV transmission and you would have the SPF number.
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| Window Films help protect you and your belongings from the suns harmful UV radiation |
However, SPF numbers are actually measured biologically with tests done on subjects' skin. It is a measure of how long it takes to achieve a certain level of sunburn relative to an area of untreated skin. But it is only UVB that causes "sunburn," not UVA which window film also blocks. (UVA is suspected of causing the most virulent forms of skin cancer.) While the computation we have described above is easy to perform with known UV transmission reduction values, two things must be said:
1) Most dermatologists don't think numbers larger than about 20 are meaningful.
2) While it is easy to calculate the reduction in UV transmission by a window film (a thousandfold reduction with the best auto and flat glass films), actual SPF numbers are officially determined by skin testing according to an established experimental protocol. It is not permissible to make such claims about actual SPF numbers without having these skin tests performed by a qualified laboratory.
All in all, the installation of one of our high performance window films will block over 99% of the suns harmful UVB radiation, resulting in a SPF factor of well over 100.
