Light pen

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

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.

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.

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

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.

The first nonlinear editor, the CMX 600 was controlled by a light pen, where operator clicked symbols superimposed on edited footage.

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 and Holborn 9100. 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 persistence, which tend to flicker.^[13]

See also

• Bit banging
• CueCat
• Digital pen
• Light gun
• Pen computing
• Stylus (computing)

Notes

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

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. 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. 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. Archived from the original on 2022-12-12. 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