•A two-way mirror (also, one-way mirror or one-way glass) is a mirror which is partially reflective and partially transparent. When one side of the mirror is brightly lit and the other dark, it allows viewing from the darkened side but not vice versa. The glass is coated with, or encases, a thin and almost-transparent layer of metal (usually aluminium). The result is a mirrored surface that reflects some light and is penetrated by the rest.
•When one side is brightly lit and the other kept dark, the darker side becomes difficult to see from the brightly lit side because it is masked by the much brighter reflection of the lit side.
