A Moment of Science

One Way Glass

Today we will unveil the magic behind one-way glass. The trick is simpler than you might think. Learn more on this Moment of Science.

Looking through one-way glass

Photo: Darkumber (flickr)

One-way glass like this only works if the suspect's room is brightly lit up, while the other side must be dark

Today we will unveil the magic behind one-way glass.

The trick is simpler than you might think. Most mirrors are made by applying a thin layer of a reflective material, aluminum in most cases, to the back of a sheet of glass. This is called back silvering, and it makes the glass opaque.

When we look in a mirror, our image is reflected by the aluminum, which is made more durable by its glass covering.

In one way glass, the reflective material is applied less densely. This is called half- silvering. The effect is that the glass is not completely opaque like a traditional mirror. About half the light striking the glass passes through it, and the other half is reflected.

Now for the second trick to one-way glass, the lighting. The room the suspect is in is kept bright, so that the reflective quality of the glass prevails. The room on the other side of the glass is kept dark, so that instead of their reflections, the detectives see what is illuminated on the suspect’s side of the glass, or the suspect.

What if the light were to be turned up on the detective’s side, or turned down on the suspect’s side? Well, the magic would fizzle, and glass would become a window for both parties.

  • http://twitter.com/ShaneyLi Shaney Li

    cool!

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