I'd try lighting them with with lightsources aswell, so it doesnt looked as blocked out, and there would be some light shining into the rooms from the outside aswell, that would be sweet
The original plan is to have "normal" lighting be 0.0, with blindingly bright light at 1.0, and pitch-black darkness at -1.0.
The way certain things work (things beyond my control, as they are independent of my own code), I'm thinking maybe of changing my lighting range from 1.0 -> 0.0 -> -1.0, to something more compatible: 1.0 -> 0.5 -> 0.0.
That change (which I have been considering apart from the suggestion you presented) would certainly make something like what you're talking about considerably easier. Currently, the light sources work as a modifier to ambient lighting -- if a light source has less brightness than the current area, it is simply ignored (but can still affect nearby areas in which the light source has greater brightness than the area). On the other hand, a light-source with greater brightness than an area will affect that area, making it lighter.
That much is an easy assumption; but, it gets kind of goofy when you use 0.0 as your "default" setting for ambient lighting. The outside area pictured in the lighting demo images has ambient lighting of 0.0. I have it set so that the lighting is rendered based on the absolute-value of it. So, if you have a lighting of 0.25, and a lighting of -0.25, they are handled in exactly the same way -- the only difference is that if you are in an area with "default" ambient lighting (0.0), it throws things off.
To achieve the effect as it stands, I test whether light is above zero or below zero: If it is above zero, fill the area with white; if it is below zero, fill the area with black. Then I use the absolute-value of the brightness setting of lighting to determine the opacity of the area's lighting. So, an area with 0.25 lighting shows up brighter (as it is drawn-over by a white fill with 0.25 alpha) than an area with -0.25 (as it is filled with black, at 0.25 alpha).
Works, but like I said, it does cause some issues in certain situations. I would probably be better-served using 0.5 as the median value and just adjust for that when needed, rather than stick with what I'm doing now.