cathode-ray tube (CRT)
In a colour-television tube, three electron guns (one each for red, green, and blue) fire electrons …
(credit: Encyclopædia Britannica, Inc.)
Vacuum tube that produces images when its phosphorescent surface is struck by electron beams. CRTs can be monochrome (using one electron gun) or colour (typically using three electron guns to produce red, green, and blue images that, when combined, render a multicolour image). They come in a variety of display modes, including CGA (Color Graphics Adapter), VGA (Video Graphics Array), XGA (Extended Graphics Array), and the high-definition SVGA (Super Video Graphics Array).
CRT
(1) (C RunTime) See runtime library.
(2) (Cathode Ray Tube) A vacuum tube used as a display screen in a computer monitor or TV. The viewing end of the tube is coated with phosphors, which emit light when struck by electrons.
In the past, CRT was a popular term for the entire computer display terminal. Today, "monitor" is the correct term as computer displays have shifted from CRTs to flat LCD panels (see flat panel display). Likewise, TV sets are widely available in LCD and plasma flat panel technologies. However, the CRT television is not over and done with. "Direct view" CRT sets come in wide screen, HDTV models that are more affordable and offer quality equal to or better than LCD and plasma TVs. See flat panel TV and rear-projection TV.
Electrons and Phosphors
The CRT works by heating a cathode which causes electrons to flow. Accelerating and focusing anodes turn the electrons into a fine beam that is directed to the phosphors by magnetic fields that are generated by steering coils. The viewing end of a color CRT tube is coated with red, green and blue phosphor dots, and separate "electron guns" bombard their respective colors a line at a time in a prescribed sequence (see raster scan).
The resulting color displayed on screen is determined by the intensity of the electron beams as they strike the red, green and blue phosphors at that same pixel location. See cathode and vacuum tube.
Back to the 1800s
The first oscilloscope tube was developed in 1897 by German scientist Ferdinand Braun. Using a fluorescent screen and still known as a "Braun tube" in Germany, his "cathode-ray oscilloscope" was used to display the patterns of electronic signals. Although better known for inventing the CRT, Braun shared the Nobel Prize in 1909 with Guglielmo Marconi for wireless telegraphy.
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| The Braun Tube |
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| This is one of five CRT oscilloscopes developed by Ferdinand Braun in 1897. Using a bellows, it took a strong man to evacuate the air. The successor to Sir William Crookes' vacuum tubes some 20 years earlier, these tubes used "cold" cathodes, which means they were unheated, but required a huge voltage. (Image courtesy of O'Neill's Electronic Museum) |
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| CRT Vs. Flat Panel |
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| The CRT on the right has given way to its flat panel counterpart on the left. The LCD flat panels not only take up less space, but use less energy, emit less radiation and are resistant to glare. (Image courtesy of EIZO Nanao Technologies Inc.) |
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