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:
“It was such a leafy wilderness; a place for fauns and satyrs, and where bats hung all day to the rocks, and at evening flitted over the water, and fireflies husbanded their light under the grass and leaves against the night.”
—Henry David Thoreau (1817–1862)
“I am of course confident that I will fulfil my tasks as a writer in all circumstances—from my grave even more successfully and more irrefutably than in my lifetime. No one can bar the road to truth, and to advance its cause I am prepared to accept even death. But may it be that repeated lessons will finally teach us not to stop the writer’s pen during his lifetime? At no time has this ennobled our history.”
—Alexander Solzhenitsyn (b. 1918)