Volume lighting tests with mental ray. Found this book very helpful. Its not an easy read (gets very technical) but contains an abundance of condensed knowledge that is difficult to find. If you use a version of Softimage prior to version 2011, download the .spdl files below for the required shaders.
| volumeshaders.zip |
setup
volume scatter with an IES profile
volume scatter via photons cast through refractive materials
volume light scattering through transparent materials