Cathode-Ray+Tube

A cathode-ray tube (CRT) is a vacuum tube with a narrow neck and a flat rectangular base. The screen is coated on the inside with a phosphor that emits light when struck by an electron beam.

The neck is surrounded by electromagnets and inside the neck is an electron gun. The electron beam produced by the gun is dragged across the screen a line at a time, so it covers ever horizontal line of the screen.



This action is repeated many times per second. The retinal image from each phosphor dot persists in the human brain for 0.05 seconds.

As long as the whole screen is swept in a shorter time than 0.05 seconds, the sensation of the flicker is avoided.