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:
“Put out the light, and then put out the light.
If I quench thee, thou flaming minister,
I can again thy former light restore
Should I repent me; but once put out thy light,
Thou cunning’st pattern of excelling nature,
I know not where is that Promethean heat
That can thy light relume.”
—William Shakespeare (1564–1616)
“Words are but air; the pen leaves a mark.”
—Chinese proverb.