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A weekly show where we endeavor to answer one of your big questions. This week, "bored during school" asks, “How does a two-way mirror work?”

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Hi, I'm Craig, and this is a two-way video and I'm watching you and this is Mental_floss on YouTube. Today, I'm going to ask bored during school's big question: How does a two-way mirror work?

You guys have probably seen tons of two-way mirrors in cop shows. Usually someone is being interrogated inside a room containing a mirror, but people outside that room can see into it through that very same mirror. Confusingly, two-way mirrors are also known as one-way mirrors. What?! I'll let you think about that annoying part of the English language while we roll the intro. Let's get started.


Before answering this question, I should quickly explain that I have never been arrested. I just did research, actually I didn't even do that Meredith did that. But, let's explain how a regular mirror works.

A Mirror is usually glass covering something like a sheet of silver or aluminum. When light hits that sheet it bounces off of it and you usually see a very handsome bearded man in there, well at least I do. A two way mirror also contains a sheet of metal, but it is a much thinner sheet, so light still bounces off of it and reflects on one side, but that only accounts for half the light, the other half continues through the mirror.

So let's say there's a person on each side of a two-way mirror the separates two rooms. The creepy weirdo who wants to see through the mirror will need ideal lighting conditions. The person only seeing the reflection needs to be in a very bright space, and the person looking through the mirror needs to be in a darker room. 

If lighting is similar in both places the two people will actually be able to see each other. Basically because it is a mirror all it boils down to light, you are not going to find a two-way mirror that works all the time. People that design thing like interrogation rooms need to adjust the light accordingly, very light inside and dark outside. Should we be telling you this?

Of course I am not advocating the amateur use of two-way mirrors because they have the potential to be super creepy when they are not necessary. That's hat the cops told me when I was making them.

So, I'm going to teach you how to tell is a mirror is two-way. One option is to create a really dark space around your eyes and press then right up to the mirror. By creating dark lighting you are probably able to tell whether there is another side to the mirror, and if not, you just get a good up close look at yourself, and if you love yourself like me, that's a good thing.

Another way is to observe the mirror, if it looks like it is embedded into the wall, that's cause for concern, but if it is just hanging up in front of the wall, you are probably in the clear.


Thanks for watching Mental_floss on YouTube, which is made with  the help of these nice interrogators. If you have a bug question of your own that you would like answered leave it below in the comments. See you next week.