LIGHT PEN

Typical Number in Hospital:

Cost Bands:

References: 1

Instructions may be given to a computer by the use of a light pen. This is a hand-held probe which has a light detector at its tip which is connected to the computer. If the pen is held to the face of the visual display unit the position on the screen is known to the computer by the time at which the light pen receives the pulse of light from the scanning spot as it passes underneath it. Depending on the type of computer program it is thus possible to enter graphical information into the computer or answer questions by touching particular spots on the display.

Light pens are now sometimes used with ultrasonic B-scanners and with some nuclear medicine imaging apparatus to draw round a particular organ or region of interest seen on the display. Such images of the body are normally held in a computer memory (e.g. digital scan converter) and so are readily accessible to this type of computer input. A typical application might be drawing a line around the circumference of the foetal trunk as seen on an ultrasonic B-scan. The computer program might then present a figure for the area contained, the estimated weight of the foetus, or its estimated maturity.

Light pens form an extremely fast and flexible form of computer input without the use of a keyboard.