One-way mirror
A one-way mirror, also called two-way mirror (or one-way glass, half-silvered mirror, and semi-transparent mirror), is a mirror that appears reflective from one side and transparent from the other. The perception of one-way transmission is easily achievable when one side of the mirror is brightly lit and the other side is dark. This allows viewing from the darkened side but not vice versa. History The first U.S. Patent for a one-way mirror was submitted in 1903, then named a "transparent mirror". Principle of operation The glass is coated with, or has been encased within, a thin and almost transparent layer of metal (window film usually containing aluminium). The result is a mirrored surface that reflects some light and is penetrated by the rest. Light always passes equally in both directions. However, when one side...
Wikipedia
