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:
“Modern dancers are inconvenienced by a local ordinance requiring the passage of visible light between partners.”
—State of Utah, U.S. public relief program (1935-1943)
“If you tie a horse to a stake, do you expect he will grow fat? If you pen an Indian up on a small spot of earth, and compel him to stay there, he will not be contented, nor will he grow and prosper. I have asked some of the great white chiefs where they get their authority to say to the Indian that he shall stay in one place, while he sees white men going where they please. They can not tell me.”
—Chief Joseph (c. 1840–1904)