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{{Short description|Computer input device}}
{{About|the computer input device|the pen-sized flashlight|Penlight}}
{{Use dmy dates|date=August 2021|cs1-dates=y}}
{{Use list-defined references|date=December 2023}}
[[File:HypertextEditingSystemConsoleBrownUniv1969.jpg|thumb|220px|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 [[cathode-ray tube]] (CRT) display.

Like a [[touchscreen]], a light pen allows the user to point to displayed graphic elements such as menus or buttons, or even draw directly on the screen. However, while a touchscreen acts as a sensor to detect a fingertip or stylus, a light pen serves as the sensor itself, detecting the light emitted by the CRT's phosphors.

Light pens are compatible with both [[Vector monitor|vector-based]] and [[Raster_scan|raster-based]] CRT displays. As a CRT's electron beam traverses the screen, it excites a [[phosphor]] coating within the CRT, causing it to glow. If this occurs directly under the tip of the pen, a photosensitive component such as a [[photodiode]] causes a timing signal to be sent to the computer. Using either the known position of the beam at that precise moment (in a vector-based system), or the time since the last horizontal or vertical synchronization pulses (in a raster-based system), the exact position of the pen can be derived.

== History ==

{{anchor|Lightgun}}The first light pen, at this time still called a "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.<ref name="Everett_1980"/><ref name="Roch_1996"/><ref name="Carlson_2009"/><ref name="CDE_2009"/> Light pens were a component of the [[Semi-Automatic Ground Environment|SAGE]] system, assisting in tactical real-time-control of radar-networked airspace.<ref name="Roch_1996"/>

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 this light pen was made for the 1951 to 1961 was its prime years
, where operator clicked symbols superimposed on edited footage.

[[File:A_light_pen_in_use_on_a_CGA_monitor.jpg|thumb|220px|Photo of a "Warp Speed" light pen interacting with a graphics program running on a [[Tandy 1000]] computer.]]

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 [[Monochrome Display Adapter|MDA]] (only early versions),<ref name="Kosmic_2023"/> [[Color Graphics Adapter|CGA]],<ref name="Kosmic_2023"/> [[Hercules Graphics Card|HGC]]<ref name="Elliott_2020_MDA"/> (including [[HGC+]]<ref name="Elliott_2012_HGCPlus"/> and [[InColor]]<ref name="Elliott_2012_InColor"/>) and some [[Enhanced Graphics Adapter|EGA]] graphics cards also featured a connector compatible with a light pen, as did early Tandy 1000 computers,<ref group="notes">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.</ref> the [[Thomson MO5]] computer family, the [[Amiga]],<ref name="Amiga"/> [[Atari 8-bit]], [[:Category:Commodore 8-bit family|Commodore 8-bit]], some [[MSX]] computers<ref name="MSX_2019"/> and [[Amstrad PCW]] home computers. For the MSX computers, [[Sanyo]] produced a light pen interface cartridge.<ref name="Sanyo"/>

Because the user was required to hold their arm in front of the screen for long periods of time (potentially causing "[[Touchscreen#"Gorilla arm"|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|date=January 2012}} Light pen was also perceived as working well only on displays with low persistence, which tend to [[Flicker (screen)|flicker]].<ref name="Norton_1983"/>

==See also==
* [[Bit banging]]
* [[CueCat]]
* [[Digital pen]]
* [[Light gun]]
* [[Pen computing]]
* [[Stylus (computing)]]

== Notes ==
{{Reflist|group="notes"}}

==References==
<references>
<ref name="Roch_1996">{{cite book |title=Fire-Control and Human-Computer Interaction: Towards a History of the Computer Mouse (1940–1965) |chapter=2. Lightpen and Joystick |author-first=Axel |author-last=Roch |author-link=:d:Q102435890 |others=Mindell, David |publisher=[[Massachusetts Institute of Technology]], Program in Science, Technology, and Society |pages=2–3 [2] |url=http://moon.zkm.de/hp_new/pdf/mouse.pdf |access-date=2021-08-24 |url-status=live |archive-url=https://web.archive.org/web/20210628210444/http://moon.zkm.de/hp_new/pdf/mouse.pdf |archive-date=2021-06-28}} (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]]; {{ill|Buchhandlung Walther König{{!}}Verlag der Buchhandlung Walther König|de|Verlag der Buchhandlung Walther König}} in Cologne, Germany. {{ISBN|3-88375-245-2}}.)</ref>
<ref name="Carlson_2009">{{cite web |title=A Critical History of Computer Graphics and Animation |url=http://design.osu.edu/carlson/history/lesson2.html |access-date=2009-05-04 |archive-url=https://web.archive.org/web/20090505031418/http://design.osu.edu/carlson/history/lesson2.html |archive-date=2009-05-05 |url-status=dead}}</ref>
<ref name="CDE_2009">{{cite web |title=The Computer Desktop Encyclopedia (entry for Light Pen) |url=http://lookup.computerlanguage.com/host_app/search?cid=C000401&term=light%20pen |access-date=2009-05-04}}</ref>
<ref name="Everett_1980">{{cite book |chapter=Whirlwind |author-last=Everett |author-first=Robert Rivers |author-link=:de:Robert Everett (Ingenieur) |date=1980 |title=A History of Computing in the Twentieth Century |editor-last=Metropolis |editor-first=Nicholas Constantine |editor-link=Nicholas Constantine Metropolis |display-editors=etal |edition= |publisher= |isbn= |page=375}}</ref>
<ref name="Norton_1983">{{cite book |author-last=Norton |author-first=Peter |author-link=Peter Norton |editor-last1=Culverwell |editor-first1=David T. |title=Inside the IBM PC: access to advanced features and programming |date=1983 |publisher=Brady |location=Bowie, Maryland, USA |isbn=0-89303556-4 |page=164 |chapter=8. Video Access, part 1: Characters |quote=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 {{sic|?|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. […]}}</ref>
<ref name="Amiga">{{cite web |title=2. Amiga joystick extensions |url=https://www.kernel.org/doc/html/v4.19/input/devices/amijoy.html#amiga-lightpen-pinout |access-date=2022-12-12 |website=The Linux Kernel documentation |url-status=live |archive-url=https://web.archive.org/web/20221212202955/https://www.kernel.org/doc/html/v4.19/input/devices/amijoy.html#amiga-lightpen-pinout |archive-date= 2022-12-12 }}</ref>
<ref name="MSX_2019">{{cite web |access-date=2019-05-16 |title=MSX Wiki (entry for Light Pen) |url=https://www.msx.org/wiki/Light_pen}}</ref>
<ref name="Sanyo">{{cite web |url=https://www.generation-msx.nl/hardware/sanyo/mlp-01/668/ |title=Sanyo - MLP-01 | Generation MSX}}</ref>
<ref name="Elliott_2020_MDA">{{cite web |title=Monochrome Display Adapter: Notes |author-first=John C. |author-last=Elliott |date=2020-06-08 |work=Seasip.info |url=http://www.seasip.info/VintagePC/mda.html |access-date=2016-11-23 |url-status=live |archive-url=https://web.archive.org/web/20230920194518/https://www.seasip.info/VintagePC/mda.html |archive-date=2023-09-20 |quote=}}</ref>
<ref name="Elliott_2012_HGCPlus">{{cite web |title=Hercules Graphics Card Plus: Notes |author-first=John C. |author-last=Elliott |date=2012-08-09 |work=Seasip.info |url=http://www.seasip.info/VintagePC/hercplus.html |access-date=2016-11-23 |url-status=live |archive-url=https://web.archive.org/web/20161123124757/http://www.seasip.info/VintagePC/hercplus.html |archive-date=2016-11-23}}</ref>
<ref name="Elliott_2012_InColor">{{cite web |title=Hercules InColor Card: Notes |author-first=John C. |author-last=Elliott |date=2012-08-05 |work=Seasip.info |url=http://www.seasip.info/VintagePC/incolor.html |access-date=2016-11-23 |url-status=live |archive-url=https://web.archive.org/web/20161123123816/http://www.seasip.info/VintagePC/incolor.html |archive-date=2016-11-23}}</ref>
<ref name="Kosmic_2023">{{cite web |title=IBM 5150 - Early Versions: Early Cards - Monochrome Display and Printer Adapter (MDA) |editor-first=Raymond "Ray" |editor-last=Kosmic |date=2023 |orig-date=2013 |website=minuszerodegrees.net |url=https://www.minuszerodegrees.net/5150/early/5150_early.htm |access-date=2023-12-04 |url-status=live |archive-url=https://web.archive.org/web/20231204221121/https://www.minuszerodegrees.net/5150/early/5150_early.htm |archive-date=2023-12-04}}</ref>
</references>

== External links ==
{{commonscat|Light pens}}

{{Basic computer components}}
{{Pens}}

[[Category:Computing input devices]]
[[Category:History of human–computer interaction]]
[[Category:Pointing devices]]

Light pen - Revision history

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