Light pen

Light pen is used as pointing device, which is very sensitive to light. It is pen like structure. When the light pen tip is placed against the screen, it is capable of sensing its position on the Cathode Ray Tube (CRT). The use of light pen in LCD gives bad result so it is not preferred for LCD and LED.
It is used to detect a change of brightness of nearby screen pixels when scanned by cathode ray tube electron beam and reads the timing of this event to the computer. Since a CRT scans the entire screen one pixel at a time, this helps the computer to keep track of the expected time of scanning various locations on screen by the beam of cathode ray. Then records the pen’s position from the latest timestamp.
As the tip of the pen is moved over the surface of the screen, its light sensitive elements detects the light emitted from the screen. We can select the desired option of the menu by touching light pen against desired option.
Nowadays, light pens are used in many big hotels room for the customer for selecting their choice of menu and other items. Television channels for pointing important information in the screen.

Light pen
Light pen
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