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Macintosh SE prototype

The CRT is visible in a transparent prototype of a Macintosh SE.

A cathode-ray tube (CRT) is an electrical device for displaying images by exciting phosphor dots with a scanned electron beam. CRTs were used in vintage computer monitors, televisions and oscilloscopes. The first commercially practical CRT was developed in the 1930s by Allen B. DuMont.[1] The usage of CRTs for computer displays has largely been supplanted by LCD and LED panels.[2]


A large glass envelope containing a negative electrode (the cathode) emits electrons (formerly called "cathode rays") when heated, as in a vacuum tube. The electrons are accelerated across a large voltage gradient toward the flat surface of the tube (the screen) which is covered with phosphor. When an electron strikes the phosphor, light is emitted. The electron beam is deflected by electromagnetic coils around the outside of the tube so that it scans across the screen, usually in horizontal stripes. This scan pattern is known as a raster. By controlling the current in the beam, the brightness at any particular point (roughly a "pixel") can be varied.[1]

Different phosphors have different "image persistence" - the length of time for which they glow after being struck by electrons. If the scanning is done fast enough, the eye sees a steady image, due to both the persistence of the phospor and of the eye itself. CRTs also differ in their dot pitch, which determines their spatial resolution, and whether they use interlaced video or not.[1]


  1. 1.0 1.1 1.2 Cathode ray tube at the Free On-Line Dictionary Of Computing. 2006-04-29.
  2. The rise, fall, and modern uses of CRT technology by David Herres, Test & Measurement Tips. 2019-12-17.

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