In our case, we are dealing with openings as interruptions or dissections of the space; intervening elements which fragment the whole interior closed world of the internal environment.
In order to see, light must penetrate somehow. However, to keep the inward reflective nature of the room, visual connections to outside must be avoided. Light sources in this way are more puzzling, and can conform to the lines of folds in walls and ceiling to generate variation in high to low contrast between light and shadow.
I have done a little light test with a paper model made for a different subject (showing similar characteristics of the cave shell which forms part of the environment of the room). What was noticeable was the degree to which light penetrates void as opposed to semi-transparent plane.
The crispness of shadow depended on the TEXTURE of the surfaces onto which light was reflected, as well as the ANGLE of the light source, and the DISTANCE from in this case the floor as the primary reflecting surface. what I didn't test, but which deserves equal consideration is the SCALE of the light source.
Another important thing which I noted was how these variations to the light source effected the reflectability around the rest of the internal surfaces. In order to create an anti-gravity effect where this heavy stone mass which encloses the space is simply balancing on light, it is important to keep the upper reaches of the ceiling in darkness - to maintain the perception of solidity and weight.