1. Computer Input Device: Light Pen

2. LIGHT PEN

3. An input device that utilizes a light-sensitive detector to select objects on a display screen. A light pen is 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.

4. wand used in conjunction with the computer's CRT monitor.
A light Pen is a computer input device in the form of a light-sensitive
wand used in conjunction with the computer's CRT monitor.
It allows the user to point to displayed objects, or draw on the screen, in a similar way to a touch screen but with greater positional accuracy.

5. A light pen is fairly simple to implement
A light pen can work with any CRT-based screens, but not with LCD monitor, projectors and other display device.
A light pen is fairly simple to implement
The light pen works by sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly where the scanning has reached at that moment.