How Does a One-way Mirror Work?

News
By published
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.

Follow Life's Little Mysteries on Twitter @llmysteries. We're also on Facebook & Google+.

Michelle Bryner
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.
More about planet earth

What is 'induced atmospheric vibration' and did it really cause power outages across Spain and Portugal?

Yellowstone holds potentially untapped cache of 'carbon-free' helium for rockets, reactors and superconductors

Catquistadors: Oldest known domestic cats in the US died off Florida coast in a 1559 Spanish shipwreck

See more latest
Most Popular
A cat sleeping on a ship
Catquistadors: Oldest known domestic cats in the US died off Florida coast in a 1559 Spanish shipwreck
a diagram showing the Perseus galaxy cluster
Astronomers discover giant 'bridge' in space that could finally solve a violent galactic mystery
A lot of galaxies are seen as bright spots on a dark background. Toward the left, the JWST is shown in an illustration.
James Webb Space Telescope finds a wild black hole growth spurt in galaxies at 'cosmic noon'
A top down view of the Oak Ridge National Laboratory's 1960s molten salt reactor experiment, an early precursor to the Chinese reactor.
'Rabbits sometimes make mistakes or grow lazy. That's when the tortoise seizes its chance': Chinese scientists make nuclear power breakthrough using abandoned US research
A crowd of people in Sants train station in Barcelona, Spain.
What is 'induced atmospheric vibration' and did it really cause power outages across Spain and Portugal?
Grand Prismatic Spring, Midway Geyser, Yellowstone.
Yellowstone holds potentially untapped cache of 'carbon-free' helium for rockets, reactors and superconductors
Rig shark on a black background
Do sharks make noises? An accidental discovery might just answer that question
an illustration of a satellite
China uses 'gravitational slingshots' to save 2 satellites that were stuck in the wrong orbit for 123 days
An image of the Circinus West molecular cloud
Scientists spot a 'dark nebula' being torn apart by rowdy infant stars — offering clues about our own solar system's past
A series of white military-style headstones are placed close to one another in the ground against a fence and bushes. A state historical marker is seen in the foreground.
Mass graves of Black Union soldiers slaughtered by Confederate guerrillas possibly identified in Kentucky