A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computer's 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. It was long thought that a light pen can work with any CRT-based display, but not with LCDs (though Toshiba and Hitachi displayed a similar idea at the "Display 2006" show in Japan) and other display technologies. However, in 2011 Fairlight Instruments released its Fairlight CMI-30A, which uses a 17" LCD monitor with light pen control.
Since light pens operate by detecting light emitted by the screen phosphors, some nonzero intensity level must be present at the coordinate position to be selected, otherwise the pen won't be triggered.
Famous quotes containing the words light and/or pen:
“My paternal grandmother would not light a fire on the Sabbath and piled all Sunday’s washing-up in a bucket, to be dealt with on Monday morning, because the Sabbath was a day of rest—a practice that made my paternal grandfather, the village atheist, as mad as fire. Nevertheless, he willed five quid to the minister, just to be on the safe side.”
—Angela Carter (1940–1992)
“Readers are less and less seen as mere non-writers, the subhuman “other” or flawed derivative of the author; the lack of a pen is no longer a shameful mark of secondary status but a positively enabling space, just as within every writer can be seen to lurk, as a repressed but contaminating antithesis, a reader.”
—Terry Eagleton (b. 1943)