Cathode-ray tube

A cathode-ray tube (CRT) is a <a href="/facts/Vacuum_tube/VHd1BNLq">vacuum tube</a> containing one or more <a href="/facts/Electron_gun/l6nahAeW">electron guns</a>, which emit <a href="/facts/Electron/L0KBo5cW">electron</a> beams that are manipulated to display images on a <a href="/facts/Phosphorescent/WshJFsKV">phosphorescent</a> screen. The images may represent electrical <a href="/facts/Waveform/yAskMREw">waveforms</a> on an <a href="/facts/Oscilloscope/HMdD8XVk">oscilloscope</a>, a <a href="/facts/Film_frame/27Uqo8WN">frame</a> of <a href="/facts/Video/F1AV8ben">video</a> on an <a href="/facts/Analog_television/4NJJew1c">analog</a> <a href="/facts/Television_set/8moTsqhB">television set</a> (TV), <a href="/facts/Digital_imaging/nTNga50f">digital</a> <a href="/facts/Raster_graphics/HkXNc8oI">raster graphics</a> on a <a href="/facts/Computer_monitor/NRaTDFHc">computer monitor</a>, or other phenomena like <a href="/facts/Radar/jk9BTbFA">radar</a> targets. A CRT in a TV is commonly called a picture tube. CRTs have also been <a href="/facts/Williams_tube/6uXyju6I">used as memory devices</a>, in which case the screen is not intended to be visible to an observer. The term <a href="/facts/Cathode_ray/9jRXSquS">cathode ray</a> was used to describe electron beams when they were first discovered, before it was understood that what was emitted from the cathode was a beam of electrons.
In CRT TVs and computer monitors, the entire front area of the tube is scanned repeatedly and systematically in a fixed pattern called a <a href="/facts/Raster_scan/wl7UBw02">raster</a>. In color devices, an image is produced by controlling the intensity of each of three <a href="/facts/Electron_beams/9jRXSquS">electron beams</a>, one for each additive <a href="/facts/Primary_color/F4wNk0TC">primary color</a> (red, green, and blue) with a <a href="/facts/Video_signal/F1AV8ben">video signal</a> as a reference. In modern CRT monitors and TVs the beams are bent by <a href="/facts/Magnetic_deflection/ya8MwRG3">magnetic deflection</a>, using a <a href="/facts/Deflection_yoke/7Wtg97Tr">deflection yoke</a>. <a href="/facts/Electrostatic_deflection/SBufpH3U">Electrostatic deflection</a> is commonly used in oscilloscopes.

The tube is a glass envelope which is heavy, fragile, and long from front screen face to rear end. Its interior must be close to a <a href="/facts/Vacuum/BTk3goyV">vacuum</a> to prevent the emitted electrons from colliding with air molecules and scattering before they hit the tube's face. Thus, the interior is <a href="/facts/Hard_vacuum/BTk3goyV">evacuated</a> to less than a millionth of <a href="/facts/Atmospheric_pressure/wJLMSaVG">atmospheric pressure</a>. As such, handling a CRT carries the risk of violent <a href="/facts/Implosion_(mechanical_process)/sQ2J2wQk">implosion</a> that can hurl glass at great velocity. The face is typically made of thick <a href="/facts/Lead_glass/FtgPe6r2">lead glass</a> or special <a href="/facts/Barium/IkL09XHQ">barium</a>-<a href="/facts/Strontium/ABaA5qQK">strontium</a> glass to be shatter-resistant and to block most <a href="/facts/X-ray/wseP79cN">X-ray</a> emissions. This tube makes up most of the weight of CRT TVs and computer monitors.
Since the early 2010s, CRTs have been superseded by <a href="/facts/Flat-panel_display/jw0LWETN">flat-panel display</a> technologies such as <a href="/facts/LCD_television/k6YB3J0k">LCD</a>, <a href="/facts/Plasma_display/1RqxrYBo">plasma display</a>, and <a href="/facts/OLED/219L1aMJ">OLED</a> displays which are cheaper to manufacture and run, as well as significantly lighter and thinner. Flat-panel displays can also be made in very large sizes whereas 40–45 inches (100–110 cm) was about the largest size of a CRT.
A CRT works by electrically heating a tungsten coil which in turn heats a cathode in the rear of the CRT, causing it to emit electrons which are modulated and focused by electrodes. The electrons are steered by deflection coils or plates, and an anode accelerates them towards the <a href="/facts/Phosphor/vTLjrGDE">phosphor</a>-coated screen, which generates light when hit by the electrons.

Cathode-ray tube open-in-new

Cathode-ray tube