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:
“Think what a mean and wretched place this world is; that half the time we have to light a lamp that we may see to live in it. This is half our life. Who would undertake the enterprise if it were all?”
—Henry David Thoreau (1817–1862)
“It was a fatal day when the public discovered that the pen is mightier than the paving-stone, and can be made as offensive as the brickbat. They at once sought for the journalist, found him, developed him, and made him their industrious and well-paid servant. It is greatly to be regretted, for both their sakes.”
—Oscar Wilde (1854–1900)