I am trying to get a spotlight beamed onto the stage, viewed from the audience, to have a visible shaft of light. Have tried adding fog, but this is not effective, any ideas?

Requires 8-bit transparency so not possible.
What you could try:

-Make a crossplane in the form of a beam, map it with a lightbeam texture, import it, then use the glass shader texture-influence slider and a bit of overbright on it.

Thanks, nice idea will try.