Light pen

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This article is about the computer input device. For the pen-sized flashlight, see penlight.

Photo of the Hypertext Editing System (HES) console in use at Brown University, circa October 1969. The photo shows HES on an IBM 2250 Mod 4 display station, including lightpen and programmed function keyboard, channel coupled to Brown's IBM 360 mainframe.

A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's cathode-ray tube (CRT) display.

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[1]).

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 time stamps.

History[edit]

The first light pen, at this time still called "light gun", was created around 1951–1955 as part of the Whirlwind I project at MIT, where it was used to select discrete symbols on the screen,[2][3][4][5] and later at the SAGE project, where it was used for tactical real-time-control of a radar-networked airspace.[3]

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.

During the 1960s, light pens were common on graphics terminals such as the IBM 2250 and were also available for the IBM 3270 text-only terminal.

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 MDA (only early versions),[6] CGA,[6] HGC[7] (including HGC+[8] and InColor[9]) 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 Amiga,[10] Atari 8-bit, Commodore 8-bit, some MSX computers[11] and Amstrad PCW home computers. For the MSX computers, Sanyo produced a light pen interface cartridge.[12]

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.[citation needed] Light pen was also perceived as working well only on displays with low persistance, which tend to flicker.[13]

See also[edit]

Notes[edit]

  1. ^ For example, the Tandy 1000 SX has a DE-9 light pen connector 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.

References[edit]

  1. ^ "Slashphone Article". 2006-04-20. Archived from the original on 2008-11-20. Retrieved 2008-11-12.
  2. ^ Everett, Robert Rivers [in German] (1980). "Whirlwind". In Metropolis, Nicholas Constantine; et al. (eds.). A History of Computing in the Twentieth Century. p. 375.
  3. ^ a b Roch, Axel [at Wikidata]. "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 [2]. 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 [de] in Cologne, Germany. ISBN 3-88375-245-2.)
  4. ^ "A Critical History of Computer Graphics and Animation". Archived from the original on 2009-05-05. Retrieved 2009-05-04.
  5. ^ "The Computer Desktop Encyclopedia (entry for Light Pen)". Retrieved 2009-05-04.
  6. ^ a b Kosmic, Raymond "Ray", ed. (2023) [2013]. "IBM 5150 - Early Versions: Early Cards - Monochrome Display and Printer Adapter (MDA)". minuszerodegrees.net. Archived from the original on 2023-12-04. Retrieved 2023-12-04.
  7. ^ Elliott, John C. (2020-06-08). "Monochrome Display Adapter: Notes". Seasip.info. Archived from the original on 2023-09-20. Retrieved 2016-11-23.
  8. ^ Elliott, John C. (2012-08-09). "Hercules Graphics Card Plus: Notes". Seasip.info. Archived from the original on 2016-11-23. Retrieved 2016-11-23.
  9. ^ Elliott, John C. (2012-08-05). "Hercules InColor Card: Notes". Seasip.info. Archived from the original on 2016-11-23. Retrieved 2016-11-23.
  10. ^ "2. Amiga joystick extensions — The Linux Kernel documentation". www.kernel.org. Retrieved 2022-12-12.
  11. ^ "MSX Wiki (entry for Light Pen)". Retrieved 2019-05-16.
  12. ^ "Sanyo - MLP-01 | Generation MSX".
  13. ^ Norton, Peter (1983). "8. Video Access, part 1: Characters". In Culverwell, David T. (ed.). Inside the IBM PC: access to advanced features and programming. Bowie, Maryland, USA: Brady. p. 164. ISBN 0-89303556-4. The light pen isn't one of the more popular options for the IBM/PC. […] The light pen is in a kind of a bind — it can only be used with a display which has a very low persistance. […] But that kind of display screen tends to flicker to the eye. So a good display for the eye can't use a light pen, and a light pen display is harder on the eye. […]

External links[edit]

Wikimedia Commons has media related to Light pens.
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