a rodlike device which, when applied to the screen of a cathode-ray tube, can detect the time of passage of the illuminated spot across that point thus enabling a computer to determine the position on the screen being pointed at
b.
a penlike device, used to read bar codes, that emits light and determines the intensity of that light as reflected from a small area of an adjacent surface
light pen in American English
US
a hand-held, pen-shaped electronic device used to scan images, draw lines, designate points, etc. as on a computer video screen