Definition
A thin layer of phosphorescent material applied to the inside of a cathode-ray tube (CRT) screen or similar display surface that emits visible light when struck by an electron beam or other energy source, producing the image seen by the observer.
Plain English
A glowing layer painted on the inside of a screen. When energy hits it, it lights up and shows you the picture.
Context Anchor
Seen in discussions of older aircraft radar displays, electronic instruments, and display-tube construction.
Derivation
From the Greek 'phosphoros,' meaning 'light-bringing' (phos = light, phoros = bearing). The coating literally 'brings the light' to the screen when energized.
Why Pilots Care
On legacy displays, phosphor coatings determine image brightness and persistence. A worn or aged coating produces a dim or smeared picture, which can make critical readings such as weather returns or instrument indications harder to interpret.
Analogy
It is similar to glow-in-the-dark material: when it is energized, it gives off visible light. In a display tube, the energy comes from inside the display rather than from room light.
Intuition Check
Do not think of phosphor coating as ordinary paint. Its important job is not color; it is to glow when energized so the screen can show an image.
Example Sentence 1
The radar screen had dimmed over time as its phosphor coating aged.
Example Sentence 2
Fading in the phosphor coating caused uneven brightness on the radar screen during the preflight check.