The gist of how one way mirrors work is that a piece of glass is coated with less silver than a regular mirror. This allows more light to be transmitted through the mirror. Light is still reflected, however, and, between a light and dark room, an observer in a lighted room will see an abundance of reflected light while an observer in the dark room will see an abundance of transmitted light. So, light will not bounce around forever. It will reduce in intensity until there is no observable light.
Another way to look at things is if you can see the light from the sphere, your observation is of photons hitting the photo-receptors in your eye. This means that the light had to leave the sphere and end up in your eye. So, if you can see it, then it must be leaking light (ideally speaking).