As you walk back through the brig and the column-room, you notice that nothing really seems to have changed. The lit rooms are still lit, and the unlit hallways are still dark. By the time you make it back to the gate, where the other switch was, you're really starting to wonder just what that switch there did.
Of course, when you do make it to the gate, you notice. That other hall, the one that was once dark, is now no longer. It looks like you've uncovered another path.