Light Pen

pen-shaped device that emits a beam of light and is used for choosing options or drawing directly on a computer screen (through photoelectric means)

A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with the computer's CRT monitor. It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy. A light pen can work with any CRT-based monitor, but not with LCD screens, projectors and other display devices.
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Noun
1. (computer science) a pointer that when pointed at a computer display senses whether or not the spot is illuminated
(synonym) electronic stylus
(hypernym) pointer
(classification) computer science, computing

A stylus, usually hand-held, that contains a photodetector or light source, and that allows interaction with a computer through a specially designed monitor screen.

<hardware> 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.
(2003-12-02)