Today’s Wonder of the Day was inspired by slyfox. slyfox Wonders, “How does one way glass work?” Thanks for WONDERing with us, slyfox!

Think back to the last time you looked at yourself in the mirror. Maybe you checked your hair while brushing your teeth this morning. Perhaps you flashed a big smile as you washed  your hands. Most people see their own reflection many times a day. Have you ever stopped to WONDER whether someone else might be watching you from the other side of a mirror?

Yikes! That might be a scary thought. Don’t worry, though—most mirrors don’t allow people to look at you from the other side. But if you’ve ever seen a crime suspect being questioned on a TV show, you know that some special mirrors are made to do just that. What are we talking about? One-way mirrors, of course!

How exactly do one-way mirrors work? To understand, you need to know how regular mirrors are made. Most of them go through a process called silvering. That’s when a layer of silver (or sometimes aluminum) is added to a piece of glass. This is most often done by spraying a silver solution over a glass pane until it is covered.

One-way mirrors are half-silvered. That means they have only a very thin layer of reflective coating. This allows the glass to reflect half the light that hits it. Still, half the light also goes straight through. This makes the glass both reflective and transparent

Have you ever seen a one-way mirror in action? If so, you know that typically, only the people on one side of the glass can actually see through it. Those on the other side can only see their own reflections. Why is that?

It all has to do with lighting. If you want one side of the glass to look like a normal mirror, it’s important to make sure that area is well-lit. The bright lighting will make the mirror’s surface more reflective. If the room on the other side of the glass is dimly lit or dark, there will be less reflection. People standing on that side of the glass will be able to see through it to the other side.

That’s how people on one side of a one-way mirror can watch those on the other side. For this to occur, one room needs to remain more brightly lit than the other. If both rooms have similar lighting, the one-way mirror turns into a window. People will be able to see through the glass both ways.

Have you ever looked into a one-way mirror? Did you see your own reflection? Or did you see someone standing on the other side? Detectives often find that one-way mirrors come in handy in their line of work. What other practical uses might these special mirrors have?

Standards: CCRA.L.3, CCRA.L.6, CCRA.R.1, CCRA.R.2, CCRA.R.4, CCRA.R.10, CCRA.SL.1, CCRA.SL.2, CCRA.W.7

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