The cathode ray tube (CRT) is a vacuum tube that contains one or more electron guns and a phosphorescent screen and is used to display images. It modulates, accelerates and directs electron beams onto the screen to create the images. The images can represent electrical waveforms (oscilloscopes), images (television, computer monitor), radar targets or other phenomena. CRTs have also been used as storage devices, in which case the visible light emitted by the fluorescent material (if any) should not be of significant importance to a visual observer (although the visible pattern on the tube surface may represent the stored data cryptically).

In television sets and computer monitors, the entire front area of ​​the tube is repeated and systematically scanned according to a fixed pattern, the so-called grid. In color devices, an image is created by controlling the intensity of each of the three electron beams, one for each additive primary color (red, green and blue) with a video signal as a reference. In all modern CRT monitors and televisions, the rays are deflected by magnetic deflection, a changing magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although the electrostatic deflection is usually found in oscilloscopes, a type of electronic test instrument, is used.

A 14-inch cathode ray tube with deflection coils and electron guns

Typical United States 1950s single color television

A CRT television that was shot in slow motion. The light line is drawn in a grid pattern from left to right

A flat CRT assembly in a 1984 Sinclair FTV1 pocket television

electron gun
A CRT is constructed from a glass envelope that is large, deep (i.e., long from front to back), fairly heavy, and relatively fragile. The inside of a CRT is evacuated to approximately 0.01 Pascal (9.9 x 10 -8 atm) [3] to 133 nanopascals (1.31 x 10 -12 atm) to [4] free-electron flight from the gun lighten (s) to the face of the tube. The fact that it is evacuated makes handling an intact cathode ray tube potentially dangerous, since there is a risk of the tube breaking and causing violent implosion that can throw glass fragments at high speed. For safety reasons, the face is usually made of thick lead glass to ensure a high level of break resistance and to block most X-ray emissions, especially when the CRT is used in a consumer product.

Since the end of the 2000s, CRTs have largely been replaced by newer “flat screen” display technologies such as LCD, plasma display and OLED displays, which in the case of LCD and OLED displays have lower manufacturing costs and lower power consumption, significantly less weight and volume, Flat screens can also be made in very large sizes. While 38 to 40 inches (97 to 102 cm) were approximately the largest size of a CRT television, flat screens are available in 82 inches (210 cm) and larger sizes.

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