Alight pen is acomputerinput device in the form of a light-sensitive wand used in conjunction with a computer'scathode-ray tube (CRT) display.
It allows the user to point to displayed objects or draw on the screen in a similar way to atouchscreen but with greater positional accuracy[dubious –discuss]. A light pen can work with any CRT-based display, but its ability to be used withLCDs 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 bycathode-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.
The first light pen, at this time still called "light gun", was created around 1951–1955 as part of theWhirlwind I project atMIT, where it was used to select discrete symbols on the screen,[2][3][4][5] and later at theSAGE 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 theAN/FSQ-7 for military airspace surveillance. This is not very surprising, given its relationship with the Whirlwind projects. SeeSemi-Automatic Ground Environment for more details.
During the 1960s, light pens were common on graphics terminals such as theIBM 2250 and were also available for theIBM 3270 text-only terminal.
The first nonlinear editor, theCMX 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.
Light pen usage was expanded in the early 1980s to music workstations such as theFairlight CMI and personal computers such as theBBC Micro andHolborn 9100.IBM PC-compatibleMDA (only early versions),[6]CGA,[6]HGC[7] (includingHGC+[8] andInColor[9]) and someEGA graphics cards also featured a connector compatible with a light pen, as did early Tandy 1000 computers,[notes 1] theThomson MO5 computer family, theAmiga,[10]Atari 8-bit,Commodore 8-bit, someMSX computers[11] andAmstrad 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 toflicker.[13]
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 [sic?]. […] 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. […]
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