I've recently tried to incorporate a strong element of back lighting in my portraits when possible. I think this is especially effective when the subject is a child. One might call it a halo effect. Psychologically it may suggest associations with brilliance, with inspiration, insight, and revelation.
I've used it before (see the left portrait on the header) but only coincidentally; that is, the photo I worked from provided that lighting. In this case the photo I was sent was full face on flash and I didn't even want to use it. But the pose was sweet, and I decided to take a chance and see if I couldn't alter the lighting.