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Bagginsbill's environment sphere prop emits light by plugging color into the Ambient_Color and value into Ambient_Value channels of the sphere's materials.  This works the same for any material anywhere in your scene, if it has Ambient color and value information, then it will emit light that Indirect Lighting will cast around the scene.  This is a standard feature of Global Illumination in other apps, and can give you some very interesting results that were pretty difficult to obtain in older versions, like the famous "bioluminescence" thread.  Now instead of having to set up Gather nodes everwhere you want a surface to be illuminated by a glowing material, you just make the material glow.

But you do have to go through your materials and remove ambient color and value, and remove AO nodes. Fortunately, I think there is s python tool set at RDNA which allows you to do this without too much pain. (I haven't tried those details yet since I just got Poser 8).