is a pointing device, which is used to choose objects or commands on the screen either by pressing or moving it on the surface of the screen or by pressing a small switch on its side. It is a small pen shaped wand that uses light sensor. The light sensor senses the light emitted from a limited field of view when it comes in front of a graphic element or object of the screen.
The light coming from the screen causes the photocell to respond by generating a pulse. This electric response in shape of a pulse is transmitted to a processor that identifies the pixel, the light pen is pointing. To identify a specific location, the light pen is very useful. It is also used to draw images on the screen.