Cathode ray tube
Vacuum tube display that enabled television and computing.
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A cathode ray tube (CRT) is a vacuum tube containing one or more electron guns that emit electron beams, directed and controlled to display images on a phosphorescent screen. CRTs were used in oscilloscopes, analog television sets, computer monitors, and radar displays, and also served as memory devices. They were the dominant display technology for much of the 20th century before being superseded by flat-panel displays.
The tube is a heavy, fragile glass envelope with a long rear section, evacuated to less than a millionth of atmospheric pressure to prevent electron scattering. This vacuum creates a risk of violent implosion. The front face is made of thick lead or barium-strontium glass to resist shattering and block X-rays.
A CRT works by electrically heating a tungsten coil, which heats a cathode at the rear, causing it to emit electrons. These electrons are modulated and focused by electrodes, then steered by deflection coils or plates. An anode accelerates them toward a phosphor-coated screen, which glows upon impact.
The entire screen is scanned repeatedly in a fixed raster pattern. In color devices, three electron beams control the intensity of red, green, and blue phosphors. Magnetic deflection, using a deflection yoke, is typical in monitors and TVs, while electrostatic deflection is common in oscilloscopes.
Discoveries
The term "cathode ray" originated before it was understood that the emitted rays were electrons. Cathode rays were discovered by Julius Plücker and Johann Wilhelm Hittorf, who observed shadows cast on tube walls. Arthur Schuster demonstrated deflection by electric fields, and William Crookes by magnetic fields. J. J. Thomson measured the mass-to-charge ratio, identifying electrons as subatomic particles.
The earliest CRT, the Braun tube, was invented by Ferdinand Braun in 1897 as a cold-cathode diode with a phosphor screen. Alan Archibald Campbell-Swinton later proposed using a CRT for both transmitting and receiving "distant electric vision." The first hot-cathode CRT was developed by John Bertrand Johnson and Harry Weiner Weinhart of Western Electric, becoming a commercial product in 1922, enabling lower anode voltages and higher beam currents. Kenjiro Takayanagi demonstrated a CRT TV receiver in 1926, later improving its resolution.
Quick Facts
- Invented by
- Ferdinand Braun
- Field
- Display technology
- Known for
- Foundation of television and computer monitors
- Key contributors
- Julius Plücker
- Johann Wilhelm Hittorf
- J. J. Thomson
- Vladimir K. Zworykin
Facts from the source article.
Lore & Background
The cathode ray tube is a sealed glass envelope, heavy and fragile, with a long rear section behind the front screen. Its interior is evacuated to less than one millionth of atmospheric pressure to prevent electron scattering. The face is made of thick lead glass or barium-strontium glass to resist shattering and block most X-rays.
The tube contains one or more electron guns that emit electron beams. These beams are modulated, focused, and steered by electrodes, deflection coils, or plates. An anode accelerates the electrons toward a phosphor-coated screen, which emits light upon impact.
The entire screen is scanned in a fixed raster pattern. In color tubes, three electron beams—one for each additive primary color (red, green, and blue)—are controlled in intensity. Magnetic deflection via a deflection yoke is used in monitors and TVs, while electrostatic deflection is common in oscilloscopes. The CRT was invented by Ferdinand Braun in 1897 as a cold-cathode diode with a phosphor screen.
The first hot-cathode CRT was commercialized in 1922 by Western Electric. CRTs have been used for displaying electrical waveforms, video frames, computer graphics, and radar targets, and also as memory devices. They were largely superseded by flat-panel displays after the late 2000s.
Reader's Guide
The cathode ray tube was a foundational technology for electronic displays, enabling the development of television, computer monitors, and oscilloscopes. Its ability to display electrical waveforms, video frames, and raster graphics made it central to both entertainment and scientific instrumentation. The CRT's design evolved from circular to rectangular screens, and from monochrome to color using three electron beams for red, green, and blue phosphors. The introduction of hot cathodes, rare earth phosphors, and aperture grille technology improved brightness and longevity.
However, CRTs were heavy, fragile, and required a high vacuum, posing implosion risks. By the late 2000s, flat-panel displays like LCD, plasma, and OLED replaced CRTs due to lower cost, lighter weight, and larger sizes. Despite obsolescence, the CRT remains a key milestone in the history of visual display technology.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Cathode ray tube (CC BY-SA 4.0).
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