Here's the method I have used in this new environment I've been working on...

Here you have a shaded preview of the room in Poser with the light boxes, simple geometry really, coming from the windows and their preview set to wire.

Here you have the same thing, totally viewport display here, with the shading turned on for the light boxes.

Above is a render of what they come out like using the basic setup method shown later...

Above is a render showing the same basic setup with some added clouds in the ambient color channel...

And last, here's the shader setup. It's actually really simple. Also  note that the objects this is applied to have cast shadows and raytracing turned off in their properties tab. Hope this helps! -Les