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 that shined upon the summit now seems almost to shine at our feet.”
—Woodrow Wilson (1856–1924)
“Prove that ever I lose more blood with love than I will get again with drinking, pick out mine eyes with a ballad-maker’s pen and hang me up at the door of a brothel-house for the sign of blind Cupid.”
—William Shakespeare (1564–1616)