The Super Scope makes use of the scanning process used in cathode ray tube monitors, as CRTs were the only affordable TV monitors until the early 2000s. In short, the screen is drawn by a scanning electron beam that travels horizontally across each line of the screen from top to bottom. A fast photodiode will see any particular area of the screen illuminated only briefly as that point is scanned, while the human eye will see a consistent image due to persistence of vision.