A cathode-ray tube (CRT) is a special case where this is used to generate a picture on a phosphorous screen.
The Cathode-Ray Tube is the technology used in most (2002) televisions and computer display screens. A CRT works by moving an electron beam back and forth across the inside front of the screen. Each time a beam makes a pass across the screen, it lights up phosphor dots on the inside, illuminating the active portions of the screen. The beam is controlled by electromagnetism, which causes it to scan in an orderly fashion that is related in time to the image data that causes the energy from the gun to vary, thereby producing (painting) the images you se