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:
“The light is there, and colors surround us. However, if there were no light nor colors in our own eye, we wouldn’t perceive such things outside of us.”
—Johann Wolfgang Von Goethe (1749–1832)
“Its whether will ye be a rank robber’s wife,
Or will ye die by my wee pen knife?
Its I’ll not be a rank robber’s wife,
But I’ll rather die by your wee pen knife.
He ‘s killed this may and he ‘s laid her by,
For to bear the red rose company.”
—Unknown. Babylon; or, The Bonnie Banks o’ Fordie (l. 9–14)