Quote -      A burned-out white cube is OK for lighting a room if placed above and behind the camera.  But if the light source is in camera, then the IDL emitter must emit light from the correct place -or myriad of places (Christmas tree lights)- and the white cube doesn't work.

 

Here's an example:

 

The left render shows the setup: no lights, only the ambient on the ball. The middle render is with the ball invisible to the camera. Nice, soft light, ready for adding a hologram, or a fairy, or a magic energy sphere (either in post or directly in the render). The third render is exactly the same except I added a mirror behind the hand and oops, there's the ball. And there's no way to eliminate that ball showing up in reflections.