| The CRT in a TV is a glass vacuum tube. The inner surface of the screen is coated with tiny phosphor dots that emit light in the three primary colors (red, green, and blue). These phosphor dots glow when struck by an electron beam, resulting in the images we see on screen. The electron beam is a focused stream of electrons pouring off an electrode to which negative voltage is being supplied. The electrons emitted from the so-called electron gun strike the phosphor dots, causing them to glow. Deflection coils that create magnetic fields are used to enable the electron beam to strike any phosphor dot on the screen. The common CRT TV has 525 scan lines on the screen. The electron gun "draws" odd lines, followed by even lines, 60 times a second. In short, we perceive the three glowing primary colors produced by the electron gun's drawing process as a continuous image. The drawbacks of CRT TVs are the high voltage required to emit electrons and the large, heavy devices they require, such as the electron gun. Furthermore, in order for the scanning lines to travel over large screen areas, a certain distance is required between the electron gun and the screen, effectively limiting how thin CRT TVs can be made.
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