So I'm a little confused about how sunlight fades the hide. All my windows face north and the light that does come in the window is diffuse, reflected light (and my furniture is protected leather). Can this sort of light cause fading? All the comments I've read about sunlight just touch on it by saying keep it out of direct sunlight, but what counts as direct sunlight? "beam" sunlight?

Also unrelated question, if the leather is beginning to darken from hair oils etc can that ever be reversed?