Light Pen

What is it?

A light pen is a computer input device that makes use of a light-sensitive detector in its stylus to select objects on a display screen/video terminal that it is wired to.

What is it for?

Aside from selecting objects, the light pen is also used to draw pictures. It is said to have more positional accuracy than a touch screen. A light pen functions similar to a mouse, except that with a light pen you can move the pointer and select objects on the display screen by directly pointing to the objects with the pen and pressing the pen button to make contact.

How does it work?

The screen beams light into the pen. This screen is constantly refreshing and when the user presses the button to select, the pen senses this light from the exact pixel that illuminates it. It is then able to identify the screen location. With the screen constantly refreshing it keeps updating the pen location.

The First Light Pen:

The first light pen was created in 1952 as part of the whirlwind project at MIT. The subsequent devices created were used for military purposes, such as honing in on suspicious blips on the CRT in the U.S. air defense system.