Hm, I don’t understand the initial question, because it sounds you’re trying to bypass and rebuild Inform’s lighting system from the ground up. This is too much work if it’s not necessary. It’s much easier to just add a little bit that you need.
There is a very similar recent topic over here (“I’m in the dark here”) discussing the concepts involved that you may want to read.
I wouldn’t say any more myself until you’ve elaborated a bit. Unless the room description will change depending on whether the light comes from the sun, lantern or torch, you don’t need to distinguish between them. They’ll all be ‘light’.
-Wade