Also called "screen fade" or "phosphor burn," it refers to a permanent disfiguring of areas on a computer or TV screen when menu bars or other elements remain on screen all the time. Especially on old monochrome CRTs, but also on early color CRTs, the continuous display of the same image caused the phosphors in that area to lose their ability to be re-excited by the electron gun, creating a permanent ghost-like image.
Even on Flat Panels
Although plasma and LCD displays do not use phosphors, they can suffer from a different type of screen burn. When showing wide screen movies, black bars appear at the top and bottom. Even with wide screen TVs, movies displayed in their original panoramic, cinema formats can cause letterboxing (see
letterbox). Also, when standard definition programs appear in their original format on wide screens, black bars appear at both sides (see
pillarbox).
The problem is that the pixels in the black bars are not being excited as much as the rest of the screen, and thus do not deteriorate at the same rate. After many hours of black bar viewing, when images do appear in the areas where the bars used to be, those sections may appear brighter than the rest of the screen because the pixel elements have less wear. Most noticeable on earlier plasma displays, manufacturers provide a number of ways to expand every image to fill the screen and avoid screen burn. Some TVs display gray bars instead of black. Since gray is a color to the imaging engine, all the pixels on screen are excited no matter whether the actual images fill the screen or not. See
HDTV and
screen saver.