If I move my light source, the diffuse reflection changes. It is always brightest when the surface is facing the light source. Since I moved my light to stage left, the brightest part of the sphere is now on the left.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)