Light Pens

-- Aniket Bhattacharya

A light pen is a pencil-shaped input device that are used to select

screen positions by detecting the light coming from points on the

CRT screen.

The first Light Pen was created in the year 1952 as a part of the

Whirlwind project at the Massachusetts Institute Of

Technology.

Became popular in the 1980's particularly with the Thomson MO5

computer family.

Working principles of a

Light pen

When an activated light pen is made to point at a spot on the screen the electron

beam emitted lights up that spot , which in turn, generates an electric pulse that causes

the co-ordinate position of the electron beam to be located.

USES OF LIGHT PENS

The Light pens allow the user to point to the displayed objects, or draw on the screen, in a similar way to that of the touch screen but with a greater positional accuracy.

Disadvantages--reason for Light pens becoming obsolete..

1.Works only with any CRT-based display , but not with LCD screens.

2.When pointed at the screen, part of the screen image is obscured by the hand and pen.

3.Prolonged use causes arm fatigue.

4.Gives false readings if background lighting in a room is detected.