The light pen is a light-sensitive computer input device in the shape of a pen which allows you to point at a computer screen with light, or even to draw on the screen.
Uses of Light Pens
Light pens are used in design work and by medical professionals to access and highlight medical records, and as hand-held bar code readers.
Light pens are easy to use. They have extremely good positional accuracy on a computer screen, much more than is possible with a mouse or a touchscreen. They are ergonomically designed for ease of hand movement and are excellent for all drawing and pointing tasks. They don't require extra desk space and are easily modified for use by people with disabilities. When used for bar code reading, they are lightweight, able to come in direct contact with the bar codes and have no moving parts.
Light pens are easily damaged. They can only be used on some computer screens; they do not work with LCD screens. They usually lack high resolution capability. They can be fatiguing to the hand if overused. They can impair viewing of the computer screen on which they're being used. When used as bar code readers, they have a high error rate.