Raster Scan Display

This type of display basically employs a Cathode Ray Tube (CRT) or an LCD panel for display. The CRT works just like the picture tube of a television set. Its viewing surface is coated with a layer of arrayed phosphor dots. At the back of the CRT is a set of electron guns (cathodes) that produce a controlled stream of electrons that is called electron beam. The phosphor material emits light when struck by these high-energy electrons. The frequency and intensity of the light emitted depends on the type of phosphor material used and the energy of the electrons. To produce a picture on the screen, these directed electron beams start at the top of the screen and scan rapidly from left to right along the row of phosphor dots. They return to the leftmost position one line down and scan again, and repeat this to cover the entire screen. The return of the beam direction to the leftmost position one line down that is called Horizontal Retrace.