Cathode ray tube

A Cathode Ray Tube (usually CRT for short) is a now-obsolescent display technology that was the mainstay of visual output devices for a century, until displays consisting of arrays of LEDs, etc, became available economically.

It consists of a large vacuum tube, with a large face covered with a phospor, a phosphorescent powder. An electrode at the base of the neck (back) of the tube produces a beam of electrons, which are shot into the phosphor; where the beam hits, the phosphor produces a spot of light.

The beam can be scanned across the face by means of electrostatic or magnetic control grids through which the electron beam is sent.