Most of light setup have light level setup and 2 radius, 1st, inner, when light have 100% "power" second, outer, when light is down to 0%. Way from radius 1 to 2nd can be done as linear or expotential way.
but we have 1 radius as I see ??
and is there problem to make omni invisible in render? I would like to use omni not as part of lamp design but to make additional extra light from "outside" of the scene, we can do it in enviroment map design but adding light we can make some more brighten from inside of scene model.
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