I think the biggest problem with that light is that the hair is NOT picking it up, only the skin is. So it looks out of place. The hair tells us there isn't a light source in that direction, while the skin says otherwise. The contradictory cues are confusing.

Here's a photo I took of a friend while we were messing around with the Nikon creative lighting system. (Two flashes, one on camera, one positioned as a rim light from behind left of the "figure". LOL)

Look at what the rim light does to the hair.

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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)