For light beams to show up, your atmosphere has to be of the "scattering" type.
Sth. like this:
media {scattering {1, <1,1,1>}}
Your sphere doesn't have to be hollow (as long as the camera is not inside it).
The difference: there can be no media inside a non-hollow object, so fog doesn't
show inside the sphere.
I hope this helps
Margus
