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:
“With love’s light wings did I o’erperch these walls,
For stony limits cannot hold love out,
And what love can do, that dares love attempt.”
—William Shakespeare (1564–1616)
“If writers were too wise, perhaps no books would get written at all. It might be better to ask yourself “Why?” afterwards than before. Anyway, the force from somewhere in Space which commands you to write in the first place, gives you no choice. You take up the pen when you are told, and write what is commanded. There is no agony like bearing an untold story inside you.”
—Zora Neale Hurston (1891–1960)