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 on standard format screens, black bars appear at the top and bottom. Even with wide screen TVs, movies displayed in their original panoramic, cinema formats can cause a small amount of letterboxing (see letterbox). Also, when regular programs appear in their original format on wide screens, black bars are shown at both sides (see pillarbox). The problem is that the pixels in the areas of 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, later on, 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 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 the screen are excited for any TV/video program, no matter whether the images fill the entire screen or not. See HDTV and screen saver.