WEBVTT - How do one-way mirrors work?

0:00:00.520 --> 0:00:03.600
<v Speaker 1>Welcome to brain Stuff from how Stuff Works dot com

0:00:03.600 --> 0:00:14.640
<v Speaker 1>where smart Happens. Hi, I'm Marshall Brain with today's question,

0:00:14.960 --> 0:00:18.960
<v Speaker 1>how do one way mirrors work? Just about everyone has

0:00:19.000 --> 0:00:21.479
<v Speaker 1>seen a television show or a movie in which a

0:00:21.560 --> 0:00:26.079
<v Speaker 1>criminal suspect is question while detectives watch from behind a

0:00:26.120 --> 0:00:29.240
<v Speaker 1>one way mirror. How does a piece of glass manage

0:00:29.320 --> 0:00:32.080
<v Speaker 1>to look like a mirror on one side while remaining

0:00:32.200 --> 0:00:35.839
<v Speaker 1>clear on the other. The secret is that it doesn't.

0:00:36.240 --> 0:00:39.400
<v Speaker 1>A one way mirror has a reflective coating applied in

0:00:39.440 --> 0:00:43.400
<v Speaker 1>a very thin, sparse layer, so thin that it's called

0:00:43.400 --> 0:00:47.919
<v Speaker 1>a half silvered surface. The name half silvered comes from

0:00:47.960 --> 0:00:51.680
<v Speaker 1>the fact that the reflective molecules coat the glass so

0:00:51.760 --> 0:00:55.480
<v Speaker 1>sparsely that only about half of the molecules needed to

0:00:55.520 --> 0:00:59.120
<v Speaker 1>make the glass and opaque mirror are applied at the

0:00:59.160 --> 0:01:03.680
<v Speaker 1>molecular ball. There are reflective molecules speckled all over the

0:01:03.720 --> 0:01:06.800
<v Speaker 1>glass in an even film, but only half of the

0:01:06.840 --> 0:01:11.039
<v Speaker 1>glass is covered. The half silvered surface will reflect about

0:01:11.080 --> 0:01:14.360
<v Speaker 1>half the light that strikes its surface, while letting the

0:01:14.400 --> 0:01:17.880
<v Speaker 1>other half goes straight through. It turns out that half

0:01:17.920 --> 0:01:21.679
<v Speaker 1>silvered mirrors are also essential to many types of lasers,

0:01:21.720 --> 0:01:25.640
<v Speaker 1>as well as to teleprompters. See how lasers work and

0:01:25.680 --> 0:01:30.000
<v Speaker 1>how teleprompters work at how stuff works dot com for details.

0:01:30.040 --> 0:01:33.640
<v Speaker 1>So why doesn't the criminal suspects see the detectives in

0:01:33.680 --> 0:01:36.920
<v Speaker 1>the next room. The answer lies in the lighting of

0:01:36.959 --> 0:01:40.000
<v Speaker 1>the two rooms. The room in which the glass looks

0:01:40.040 --> 0:01:43.240
<v Speaker 1>like a mirror is kept very brightly lit, so that

0:01:43.319 --> 0:01:46.720
<v Speaker 1>there's plenty of light to reflect back from the mirror surface.

0:01:47.160 --> 0:01:50.000
<v Speaker 1>The other room, in which the glass looks like a window,

0:01:50.240 --> 0:01:53.680
<v Speaker 1>is kept dark, so there's very little light to transmit

0:01:53.760 --> 0:01:56.960
<v Speaker 1>through the glass. On the criminal side. The criminal sees

0:01:57.040 --> 0:02:00.560
<v Speaker 1>his own reflection. On the detective side, the large amount

0:02:00.600 --> 0:02:03.800
<v Speaker 1>of light coming from the criminal side is what they see.

0:02:04.360 --> 0:02:07.280
<v Speaker 1>In many ways, it's the same as if people were

0:02:07.280 --> 0:02:10.639
<v Speaker 1>whispering in one room while a loud stereo were playing

0:02:10.639 --> 0:02:13.680
<v Speaker 1>in the other. The sound of the whisper might carry

0:02:13.680 --> 0:02:15.800
<v Speaker 1>into the room with the stereo, but it would be

0:02:15.919 --> 0:02:19.160
<v Speaker 1>drowned out by the intensity of the music. If the

0:02:19.280 --> 0:02:22.320
<v Speaker 1>lights in the room with the mirror are suddenly turned out,

0:02:22.840 --> 0:02:25.960
<v Speaker 1>or the lights in the observation room suddenly turned on,

0:02:26.440 --> 0:02:29.120
<v Speaker 1>then the one way mirror becomes more like a window,

0:02:29.480 --> 0:02:32.280
<v Speaker 1>with people in each room able to see those on

0:02:32.360 --> 0:02:35.800
<v Speaker 1>the other, or if you reverse the lighting, the mirror

0:02:35.840 --> 0:02:40.000
<v Speaker 1>side switches to the detective side and the criminal can

0:02:40.040 --> 0:02:44.519
<v Speaker 1>look through and see the detectives. Be sure to check

0:02:44.520 --> 0:02:47.639
<v Speaker 1>out our new video podcast, Stuff from the Future. Join

0:02:47.760 --> 0:02:50.239
<v Speaker 1>how Stuff Work staff as we explore them as promising

0:02:50.320 --> 0:02:54.959
<v Speaker 1>and perplexing possibilities of tomorrow. The House Stuff Works. I

0:02:55.040 --> 0:02:58.160
<v Speaker 1>Find app has arrived down at it Today on iTunes