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:
“So doth, so is Religion; and this blind-
ness too much light breeds; but unmoved thou
Of force must one, and forc’d but one allow;
And the right; ask thy father which is she,
let him ask his; though truth and falsehood be
Near twins, yet truth a little elder is;”
—John Donne (1572–1631)
“Go on then in doing with your pen what in other times was done with the sword; shew that reformation is more practicable by operating on the mind than on the body of man.”
—Thomas Jefferson (1743–1826)