Monochromatic Displays Discussions about VDTs are often limited to monochromatic raster scan CRT displays. This type of display is the most common, but there are a variety of CRT displays and technologies that may be used for VDTs. Here are brief descriptions of some of them. Raster scan A raster scan CRT works much like a television set. Light occurs when an electron beam stimulates a phosphor.
Phosphors are inorganic crystalline materials that convert electron energy to light energy.
The electron energy beam is swept horizontally across the phosphor. After each sweep the beam is moved down an increment and swept across the phosphor again. After the bottom line is swept, the beam returns to the top and the sweep process begins again. Symbols on the display are made by turning the beam on and off as it sweeps over the phosphor. At close range, this can be seen as a series of horizontal lines on a television set.