system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do older television sets emit a brief flash of white light when being turned off?
gpt
The older CRT (Cathode Ray Tube) TV's and monitors work by using an electron gun to shoot differently charged electrons at a phosphorescent material, which is then screened to make pixels. Depending on the charge of the electron, it makes either a red, green or blue pixel, or any combination of the three. This beam of electrons is controlled by a strong magnetic field, which "scans" the beam across the surface of the screen in horizontal lines. When you turn the TV on, the magnetic field is created immediately, but the ray gun takes a few seconds to warm up and start firing, hence the slow buildup. When the set is then turned off, the magnetic field collapses instantly, but the ray gun still emits particles for about a second. Without the magnetic field to guide them, they all hit in one focused beam instead of diffused lines, causing all the phosphorescent material to fire at once, hence the white flash.