Physics 2000 Einstein's Legacy TV Screens

The Big Picture

One time I tried to take a picture of my favorite television show and the photo only showed about a quarter of the picture on the screen. Why did that happen?

That is a very good question, Kyla. There are a few things you need to know about before I can answer that. First, you can think of the image on your television screen as a collection of many dots of light.

Then why do I see the whole picture? How do these dots form the image? Look at this picture from far away, and then zoom in for a closer look.

Now I see them! They were just too small for me to see individually before. But that doesn't explain why only some of them showed up on my photograph. There must be something else going on.

You're right. The reason you didn't see the whole picture is because not all of the dots are shown at the same time. Take a look at the following demonstration.

Oh I get it! The faster the dots are lit up, the more it looks like what I see on my television.

Yes, if the dots light up fast enough our eyes don't see a sequence of dots, but they all look like they are lit at once. This happens because we continue to see a dot as lit up for a short time after it has become dark. It's called persistence of vision.

I understand how this works for still images, but TV isn't a slide show. That's why we need to start thinking about how this applies to moving images, and how your television screen shows them.

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