Light Pen

A light pen is a pointing device. It is used to select a displayed menu option on the CRT. It is a photosensitive pen like device. It is capable of sensing a position on the CRT screen surface, its photocell sensing element detection the light coming from the screen and the corresponding signals are sent to the processor. The menu is a set of programmed choice offered to the user.
A light pen can also be used for graphics work. A user can draw directly on the CRT screen with the light pens.