This scene looks familiar(ish)
http://www.indigorenderer.com/joomla/in ... ewsIndex=1
To your question: put your exit portals behind every single window or opening. (Not behind the door, as there is an other room, but everywhere, where there's no scene behind

)
the normal should point through the window, into the direction, the light is supposed to flow.
And it's invisible, so, you can't texture it
