It allows the user to point to displayed objects or draw on the screen in a similar way to a touchscreen but with greater positional accuracy. A light pen can work with any CRT-based display, but its ability to be used with LCDs was unclear (though Toshiba and Hitachi displayed a similar idea at the "Display 2006" show in Japan).
A light pen detects changes in brightness of nearby screen pixels when scanned by cathode-ray tube electron beam and communicates the timing of this event to the computer. Since a CRT scans the entire screen one pixel at a time, the computer can keep track of the expected time of scanning various locations on screen by the beam and infer the pen's position from the latest timestamp.
The first light pen, at this time still called "light gun", was created around 1945–1955 as part of the Whirlwind I project at MIT, where it was used to select discrete symbols on the screen, and later at the SAGE project, where it was used for tactical real-time-control of a radar-networked airspace.
One of the first more widely deployed uses was in the Situation Display consoles of the AN/FSQ-7 for military airspace surveillance. This is not very surprising, given its relationship with the Whirlwind projects. See Semi-Automatic Ground Environment for more details.
Light pen usage was expanded in the early 1980s to music workstations such as the Fairlight CMI and personal computers such as the BBC Micro. IBM PC compatible CGA, HGC and some EGA graphics cards also featured a connector compatible with a light pen, as did early Tandy 1000 computers,[notes 1] the Thomson MO5 computer family, the Atari 8-bit, Commodore 8-bit, some MSX computers and Amstrad PCW home computers. For the MSX computers, Sanyo produced a light pen interface cartridge.
Because the user was required to hold their arm in front of the screen for long periods of time (potentially causing "gorilla arm") or to use a desk that tilts the monitor, the light pen fell out of use as a general-purpose input device.
- For example, the Tandy 1000 SX has a DE-9 light pen conector on the rear panel; on the later-introduced Tandy 1000 TX, this light pen interface has been replaced with a serial port using the same connector in the same location.
- "Slashphone Article". 2006-04-20. Archived from the original on 2008-11-20. Retrieved 2008-11-12.
- Everett, Robert Rivers (1980). "Whirlwind". In Metropolis, Nicholas Constantine; et al. (eds.). A History of Computing in the Twentieth Century. p. 375.
- Roch, Axel. "2. Lightpen and Joystick". Fire-Control and Human-Computer Interaction: Towards a History of the Computer Mouse (1940–1965) (PDF). Mindell, David. Massachusetts Institute of Technology, Program in Science, Technology, and Society. pp. 2–3 . Archived (PDF) from the original on 2021-06-28. Retrieved 2021-08-24. (1+10 pages) (NB. This is based on an earlier German article published in 1996 in Lab. Jahrbuch 1995/1996 für Künste und Apparate (350 pages) by Kunsthochschule für Medien Köln mit dem Verein der Freunde der Kunsthochschule für Medien Köln; Verlag der Buchhandlung Walther König in Cologne, Germany. ISBN 3-88375-245-2.)
- "A Critical History of Computer Graphics and Animation". Archived from the original on 2009-05-05. Retrieved 2009-05-04.
- "The Computer Desktop Encyclopedia (entry for Light Pen)". Retrieved 2009-05-04.
- "MSX Wiki (entry for Light Pen)". Retrieved 2019-05-16.
- "Sanyo - MLP-01 | Generation MSX".
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