Poser already has that, like I said in my previous post, you just use the ambient channel of the material.

Anything from 0 to 1 gives the material ambience but it doesn't give off ambience.  Anything above 1 adds extra power and it starts giving off light.  You can apply a plain white material to a cube and use it as a real area light.  It's already fully adjustable on a per object and per material basis.