No one said to use a backdrop...but in the readme it says that it only affects objects...in my early, terrible renders, I used a transparent cone, but I had the volume density too high, so it washes all out as its too bright. that last one has a backdrop, and you can see it in the one by alamanos. BUT, Anthony stated you only need the light..so I'm still not sure about the whole deal :) I have another rendering with turbulence in the volume color channel...but when you look at it, the light appears to be only at the backdrop, not enveloping the character.

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Whatever we do to the web, we do to ourselves. All things are bound together.
All things connect......Chief Seattle, 1854