A window is present in each cell that lets light in from the outside, creating backlighting to the inmates in the cells. In other words, the Panopticon is designed in a way to ensure no prisoners can see the guard in the central tower, while the guard is able to observe every prisoner in the cells without ever being seen. The inmate can never know when he is being surveilled, nor can he communicate with neighbouring prisoners. "[The prisoner] is seen, but he does not see; he is the object of information, never a subject in communication." (312) The visible but unverifiable nature of the surveillance is the principle that underlies the power of the Panoptic model. There is no need to use external force to discipline the inmates, but the inmates will discipline themselves due to mental instability of the fear of being observed. The inmate's power is turned back on themselves. "Hence the major effect of the Panopticon: to induce in the inmate a state of conscious and permanent visibility that assures the automatic functioning of power." (312) The unverifiable nature also means that the presence of the observer in the tower is not necessary for the system to take effect. "So to arrange things that the surveillance is permanent in its effects, even if it is discontinuous in its action; that the perfection of power should tend to render its actual exercise unnecessary" (312) Not only is it powerful in this way, it is also economical and effective as it is to be exercised by just one or a few people while able to exert its effect on a whole population. The panoptic model seems to provide a powerful system in which self-discipline can be ensured through the constant possibility of surveillance. It is also productive in a sense that it can help to maintain order as well as enable systems to run smoothly and effectively.
There are in fact many examples of the use of the panoptic model in our society.