light pen

A light pen or light pen is a peripheral device for computers and personal computers( PC) for data acquisition on the screen.

The light pen has an optical sensor in the tip that scans the electron beam from raster screens. When the electron beam reaches the point where the light pen touches the screen during line-by-line image composition, the brightness signal is converted into an electrical signal via the sensor and the position of the light pen is determined from this.

Use of a light pen on the screen, photo: Psychological testing

The presentation with a light pen is an older technique and is or was used in presentations to fade in markings or notes within graphics. A more advanced technique is that of the surface pen.