Q27. How is a light pen used? Is it an input or output device?
Ans. The light pen consists of a photon cell mounted pen shaped tube. The pen is brought in front of a picture element on the screen, 8 senses light coming from a limited field of view. The light coming from the screen causes the photo cell to respond by generating a pulse. This electric response is transmitted to a processor that identifies the pixel( graphic point ) the light pen pointing to. Clicking is performed by pressing the pen on the screen.
Light pen is a output device.