I've found that even indirect sunlight causes fading. I have a wall of fabric baskets to hold projects. None of them are ever in direct sunlight, but after 12 yrs they are all faded slightly. You can tell when the baskets are turned around, the fabric at the back is the same as it was years ago, but the front is faded. The light and UV rays are reflected off the window blinds. I don't mind so much that the fabric basket is faded, as long as projects inside stay protected.