cathode-ray tube

cathode-ray tube (CRT) A display device in which a beam of electrons (cathode rays), emitted by an electron gun, is focused and deflected to a series of specific positions on the phosphor-coated screen of the display. The image is generated as the electron beam moves over the screen (see also raster-scan display, vector display, beam deflection). Electrons striking a spot of phosphor on the screen increase the phosphor's energy state so that it becomes excited. The excited phosphor emits light as it returns to its ground state, thus creating a small area of the image. As light is emitted for a short period, it is necessary to provide some mechanism for continually redrawing or refreshing, the display if a constant image is required. Different phosphors emit different colored light. By coating the screen with small areas of red, green and blue phosphors and having three electron guns it is possible to produce a color display (see also RGB color model, shadow-mask cathode-ray tube).

The CRT is the most widely used computer display device, with at least 200 million in use worldwide. It is also used in TV sets whose numbers are not included in the above figure). As costs of flat-panel displays fall they are eventually expected to replace the CRT in most applications. However this prediction has been current for at least the past 25 years so a complete replacement of the CRT may be some way off.