Question

With the aid of a diagram, explain how “one way mirror works” and how can be improved.  

Answer 1

A one-way mirror has a reflective coating applied in a very thin, sparse layer -- so thin that it's called a half-silvered surface. The name half-silvered comes from the fact that the reflective molecules coat the glass so sparsely that only about half the molecules needed to make the glass an opaque mirror are applied.

The room in which the glass looks like a mirror is kept very brightly lit so that there is plenty of light to reflect back from the mirror's surface. The other room, in which the glass looks like a window, is kept dark, so there is very little light to transmit through the glass.

If the lights in the room with the mirror are suddenly turned out, or the lights in the observation room suddenly turned on, then the one-way mirror becomes a window, with people in each room able to see those in the other. You can see this effect in any mirrored office building at night -- if the light is on in an office, you can see into the office just fine.

The effect of a one-way mirror can be improved by keeping a large lighting difference between the two sides of the mirror.