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:
“Accursed who brings to light of day
The writings I have cast away.”
—William Butler Yeats (1865–1939)
“Well, I know you haven’t had much experience writing and none at all in pictures. But I’ve heard about you. It all sounded like you’re just the man I wanted for a story about the Navy. I don’t want a story just about ships and planes. I want a story about the officers.... I want this story from a pen dipped in salt water not dry martinis. Do you know what I mean?”
—Frank Fenton, William Wister Haines, co-scenarist, and John Ford. John Dodge (Ward Bond)