How do TV screens work? How are the modern ones different from the early ones?
In: Technology
Early TVs used an electron beam (a bunch of electrons accelerated very fast) to make dots of phosphor glow. Electrons can only travel very far in a vacuum, so you’d make a hollow glass “ball”, suck out all the air, stick an electron gun on one side and paint the inside of the other side with phosphor, and use fancy electronics to move the beam around to “paint” a picture on the phosphor. The dots glow for a little while after the beam hits, so by moving the beam *really* fast you could make it look like a stable picture.
Colour TVs have three electron guns, one for each colour, and three colours of phosphor (red, green, and blue). By adjusting how brightly each dot lights up (by adjusting the electron beam power), you get a very wide range of colours.
Part of the challenge here is that big glass balls with no air in them like to get crushed by atmospheric pressure, and we don’t like the screen to be a ball, we want it flat (ish). This makes old-style large TVs *really* heavy, because it takes a lot of glass to hold back the vacuum against a nearly flat screen.
To get bigger than about 35″, we had to get away from electron guns and vacuum tubes. There were two major ways to do this…build a smaller TV and project that image onto a bigger screen, which is how the original flat screens worked, or find a way to control the individual dots directly.
All modern TVs work the latter way…we build a huge array of very tiny lights (LEDs now, plasma in the past), or a huge array of very tiny shutters (LCDs) with a bright white light behind them and colour filters in front, then we use every more sophisticated electronics to turn all the tiny lights on and off (or open/close the tiny shutters) to make an image.
After that, it’s all scaling up or down.
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