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:
“For it is wretchedness that endures, shedding its cancerous light on all it approaches:
Words spoken in the heat of passion, that might have been retracted in good time,
All good intentions, all that was arguable.”
—John Ashbery (b. 1927)
“To give an accurate and exhaustive account of that period would need a far less brilliant pen than mine.”
—Max Beerbohm (1872–1956)