light pen

light pen

A light-sensitive stylus wired to a video terminal used to draw pictures or select menu options. The user brings the pen to the desired point on screen and presses the pen button to make contact. Contrary to what it looks like, the pen does not shine light onto the screen; rather, the screen beams into the pen. Screen pixels are constantly being refreshed. When the user presses the button, the pen senses light, and the pixel being illuminated at that instant identifies the screen location.

Light Pen

Light pens provide a very precise pointing capability directly on the screen.

First Light Pen

This handmade prototype of a "light gun" in 1952 was part of the Whirlwind Project at MIT. Subsequent devices were used to hone in on suspicious blips on the CRT in the U.S. air defense system (see Whirlwind and SAGE). (Image courtesy of The MITRE Corporation Archives.)

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light pen

Computing

a. a rodlike device which, when applied to the screen of a cathode-ray tube, can detect the time of passage of the illuminated spot across that point thus enabling a computer to determine the position on the screen being pointed at

b. a penlike device, used to read bar codes, that emits light and determines the intensity of that light as reflected from a small area of an adjacent surface

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light pen [′līt ‚pen]

(electronics)

A tiny photocell or photomultiplier, mounted with or without fiber or plastic light pipe in a pen-shaped housing; it is held against a cathode-ray screen to make measurements from the screen or to change the nature of the display.

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(hardware)

light pen - An early pointing device which the user pointed at a raster-scanned display screen. A photocell in the pen detected the flying spot of the raster scan. The position of the spot at that instant, obtained from the scanning electronics, was made available to software as (x, y) co-ordinates.