Refraction still might do something with how light falls off of an object when the angles approach that tangent with the line of sight, even when an object is not transparent. But I've yet to test that hypothesis. Perhaps someone with a stronger 'puter render a few spheres under varying conditions and settings to test it. But then again it just might be an unfounded thought.

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Barbequed Pixels?

Your friendly neighborhood Wings3D nut.
Also feel free to browse my freebies at ShareCG.
There might be something worth downloading.