It seems to me like the light source direction in most UI designs comes from the top or top-left. This is like the de facto standard, but I'm curious as to if anyone has ever successfully made designed where the light source comes from the bottom or bottom-right, without confusion.
If you have ever seen those optical illusions where you can switch from seeing a convexed object to seeing a concaved object. If most users expect the light source to come from the top-left they will choose to see everything as "inverted" in a design which the light source direction is bottom-right.
Thoughts on this would be very much appreciated. If you have ever seen a bottom-right lighted design, please share. Let me know if it's a bad idea to venture out into this area, and if it's best to stick with the de facto standard.