How Does a One-way Mirror Work?

mirror, one-way mirrors
One-way mirrors are designed to allow a view from one side. (Image credit: InnervisionArt, Shutterstock)

How can the good guys see through the mirror while the bad guy sees nothing but a shiny surface?

The mirror used in your favorite detective show has a thin layer of partially reflective coating. Only about 80 percent of the light is reflected, while 20 percent passes through. Importantly, the suspect’s room is about 10 times brighter than the spying detectives’ room, so the light that passes through the mirror is enough to give the detectives a good look at the suspect.

Because the detectives’ room is not as bright, the scant amount of light that passes through into the very bright room is not enough to create an image.

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Michelle Bryner
Michelle writes about technology and chemistry for Live Science. She has a Bachelor of Science in Chemistry from the Salisbury University, a Bachelor of Chemical Engineering from the University of Delaware and a degree in Science Journalism from New York University. She is an active Muay Thai kickboxer at Five Points Academy and loves exploring NYC with friends.