Ever wonder how a two way mirror works. The concept behind a mirror that you can see through on one side but not the other is surprisingly simple. It all has to do with how light is reflected on the sides of the mirror. The most important thing to realize is that there is no difference between one side of the mirror and the other. Two way mirrors work because the observer on one side sits in a darkened room while those being observed sit in a brightly lit room. Most of the light waves from the bright room are reflected back but some get through the mirror and into the dark room. Very little light hits the mirror from the dark room to reflect back so an observer in the dark room does not see their own reflection but a dimmer image of what is going on in the well lit room.