The basic idea (as I understand it) is that light bounces around in real evironments, lighter objects deflecting more light, darker ones absorbing. Bryce doesn't do this, but by giving the reflective surfaces (in my pic, everything but the sand) something to reflect besides the Bryce sky and a plane (a picture of a room, for example) it fakes the idea. A sphere is used because it can surround everything in the scene a make it look like the objects are in a more complex environment. I'm afraid someone else might explain this better. :^)

This is not my "second childhood". I'm not finished with the first one yet.

Time flies like an arrow; fruit flies like a banana.

"I'd like to die peacefully in my sleep like my grandfather....not screaming in terror like the passengers on his bus." - Jack Handy