A light pen is a device connected to a computer, that when pointed at a computer display senses whether or not the spot is illuminated. It then sends the information to the computer. The first light pen was used around 1957 on the Lincoln TX-0 computer at the famed Lincoln Labs at MIT. Light pens became moderately popular during the early 1980s but largely faded later in the decade with the rise of mouse-based WIMP interfaces as well as changes in monitor technology.
See also: Graphics tablet