Gibson Light Pen for the Apple IIe
The light pen made by Koala works as an input device for a computer, by pointing right at the monitor screen. It does not produce light, but its tip has a light-sensitive cell to detect the presence or absence of light. Somehow it can also communicate its screen position to the computer.
Drawing directly on monitor screens in graphic applications is analagous to an artist with a canvas, but it could be tiring. The light pen has its own interface card which connects right to the motherboard. It requires graphic applications to run.
Steve Gibson subsequently programmed a light pen and graphics application for the Atari in 1984, which he found to be a joy to work with compared to the Apple with its 'Wozni-isms'.
Light pens used to be available only on five digit priced graphics systems, but reached the home user with under $100 pricing in the early eighties. Similar technology is still in use -- I saw a wait person record my order using one. Or perhaps it was a stylus with a touch screen...