cathode ray tube
CRT

    (CRT) An electrical device for displaying images by
   exciting phosphor dots with a scanned electron beam.  CRTs are
   found in computer VDUs and monitors, televisions and
   oscilloscopes.  The first commercially practical CRT was
   perfected on 29 January 1901 by Allen B DuMont.

   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.

   Different phosphors have different "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 in whether
   they use interlace or not.

   (1994-11-17)