How do I test poly-tarp to see if it is UV proof? Answered

I have a canopy structure/carport that I wish to use as a wind and sun shelter for Burning Man, but I don't know if it's UV proof (I no longer have the box and the instruction book calls it a "canopy" not a "carport" and doesn't mention UV at all). The cover is white polyethylene tarp, which has to be specially treated for UV protection, I think. Does anyone know of a simple way to test for UV protection?