The term light pen has several meanings. First, it refers to a battery-operated illuminated pen that has an LED lamp in the tip in order to make it possible to write in the dark. Second, it refers to pens used for creating light “doodles” for long-exposure photography. Third, it is used by some to refer to a tablet pen for interacting with a computer through a peripheral tablet, whether or not light is actually used in the operation of the tablet pen. Fourth, and most frequently, it is an input device that allows a user to interact with a computer display.
The light pen prototype was made by the Whirlwind Project at the Massachusetts Institute of Technology (MIT). Whirlwind was a 1950s computer prototype for the United States air defense system, and the light pen — shaped like a gun with a grip attached below the barrel of the pen — was used to select blips on the CRT (cathode ray tube) screen as part of that system.
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The light pen works as a receptor functioning in connection with a computer display. The button on the pen is pressed as it makes contact with a point on the display. Then, when the pixel that the pen is marking refreshes, the light burst identifies the location, transmitting information connected with that location, identifying the x and y coordinates. The pen can be used to select items on the display or to draw on the display. The opportunity to be able to interact “naturally” as one does with a pencil or pen, rather than with a keyboard or mouse, was seen as a great advance.
Light pens enjoyed a heyday in the early 1980s, but the ergonomic strain of holding the pen to a screen over time limited their use. However, they are still in use in the television show Jeopardy as the tool with which contestants write their wagers, as well as in some industries. The arenas in which the pen continues in use include retail sales in point-of-sale (POS) applications, kiosks, gaming, graphic arts, and healthcare applications. New innovations in light pens include models that combine the technology with a barcode scanner.