How CRT TVs Work
The cathode ray tube (CRT) was invented by the German scientist Karl Braun in 1897 and, for 100 years or more, formed the basis of almost all consumer TV sets. Essentially, a cathode ray tube consists of a vacuum tube --- a conical glass tube, from which all, or most, of the air has been removed --- with a negatively charged electrode, or cathode, at one end and a phosphorescent screen at the other.
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Incoming Signal
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A CRT TV receives incoming signals from a rooftop aerial, satellite dish or underground fiber optic cable, just like any other type of TV. Electronic circuitry inside the TV splits the incoming signals into separate video and audio components and passes each to its own, separate circuit for further processing. The video signal is divided into individual red, blue and green components, which are used to drive three devices known as electron guns.
Electron Gun
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The electron guns emit negatively charged particles, called electrons --- originally known as cathode rays --- which pass through a ring of electromagnets. The electromagnets accelerate, focus and control the electron beams, so that they sweep, or scan, back and forth across the screen, line by line. The odd-numbered lines are scanned first, followed by the even-numbered lines, in a process known as interlaced scanning.
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Phosphor
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The electron beams pass through a grid of holes, known as a mask, which directs them to specific locations on the screen. Where the electron beams strike the phosphor coating on the screen, its atoms become energized, or excited, causing them to emit red, blue or green visible light according to the color of the phosphor. The pattern of red, blue and green dots creates a picture on the CRT TV screen. The brightness of the picture is determined by the volume of electrons emitted by the electron guns.
Limitations
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The picture quality provided by a CRT TV is typically good, but, because the screen is curved at the edges, some distortion may occur when the screen is viewed from certain angles. The main limitation of the CRT TV, however, is the presence of the bulky CRT, itself, which means that it is impractical to build a CRT TV with a screen size more than 40 inches. Flat panel liquid crystal display (LCD) and plasma TV screens, by contrast, use entirely different technologies that enable them to remain thin and lightweight at screen sizes well above 40 inches.
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