Does anyone know how to go about cleaning a light like this? It came with the house so we don't have any care instructions. We can't work out what bits to unscrew and what does/ doesn't come apart. It's just one glass sphere in one piece and the hole in the top appears too small for the actual light fitting to come through. That's after we've found a way to access it - quite high up at the top of a stairwell. Any tips gratefully received!