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:
“Lady of light, I would admit a dream
To you, if you would take it in your hand.
Will you not let it in a gentle stream
Of living blood? How else may I remand
Your light if not as pulse upon your ear?”
—Allen Tate (1899–1979)
“With a pen in my hand I have successfully stormed bulwarks from which others armed with sword and excommunication have been repulsed.”
—G.C. (Georg Christoph)