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:
“As I walked on the railroad causeway, I used to wonder at the halo of light around my shadow, and would fain fancy myself one of the elect. One who visited me declared that the shadows of some Irishmen before him had no halo about them, that it was only natives that were so distinguished.”
—Henry David Thoreau (1817–1862)
“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)