Screen burn-in, image burn-in, ghost image, or shadow image, is a permanent discoloration of areas on an electronic visual display such as a cathode-ray tube (CRT) or organic light-emitting diode (OLED) in a computer monitor or television set. It is caused by cumulative non-uniform use of the screen. Newer liquid-crystal displays (LCDs) may suffer from a phenomenon called image persistence instead, which is not permanent. One way to combat screen burn-in was the use of screensavers, which would move an image around to ensure that no one area of the screen remained illuminated for too long.
Causes With phosphor-based electronic visual displays (i.e. CRT-type computer monitors, oscilloscope screens, and plasma displays), non-uniform use of specific areas, such as prolonged display of non-moving images (text or graphics), repetitive contents in gaming graphics, or certain broadcasts with tickers and flags, can create a permanent ghost-like image of these objects or otherwise degrade image quality. This is because the phosphor compounds that emit light to produce images lose their luminance with use. This wear results in uneven light output over time, and in severe cases can create a ghost image of previous content. Even if ghost images are not recognizable, the effects of screen burn are an immediate and continual degradation of image quality. The length of time required for noticeable screen burn to develop varies due to many factors, ranging from the quality of the phosphors employed to the degree of non-uniformity of subpixel use. It can take as little as a few weeks for noticeable ghosting to set in, especially if the screen displays a certain image constantly and displays it continually over time, such as a menu bar at the top or bottom of the screen. In the rare case when horizontal or vertical deflection circuits fail, all output energy is concentrated to a vertical or horizontal line on the display, which causes almost instant screen burn.
CRT
Phosphor burn-in is particularly prevalent with monochromatic CRT screens, such as the amber or green monochrome monitors common on older computer systems and dumb terminal stations. This is partly because those screens displayed mostly non-moving images, and at one intensity: fully on. Yellow screens are more susceptible than either green or white screens because the yellow phosphor is less efficient and thus requires a higher beam current. Color screens, by contrast, use three separate phosphors (red, green, and blue), mixed in varying intensities to achieve specific colors, and in typical usage patterns such as "traditional" TV viewing (non-gaming, non-converged TV usage, non-Internet browsing, broadcasts without tickers or flags, no prolonged or permanent letterboxing) are used for operations where colors and on-screen object placement approach uniformity. Modern CRT displays are less susceptible than older CRTs prior to the 1960s because they have a layer of aluminum behind the phosphor, which offers some protection. The aluminum layer was provided to reflect more light from the phosphor toward the viewer. As a bonus, the aluminum layer also prevented ion burn of the phosphor and the ion trap, common to older monochrome televisions, was no longer required.
Plasma, LCD, and OLED displays
Plasma displays produced until around 2007 were highly susceptible to burn-in, while LCD-type displays are rarely affected. The wide variation in luminance degradation with RGB-based organic light-emitting diode (OLED) will cause noticeable color drift over time (where one of the red-green-blue colors becomes more prominent). OLEDs do not need a backlight to light up; each pixel is a self-illuminating LED. The pixels on OLEDs inevitably lose their brightness over time. The longer an OLED pixel is used (illuminated), the dimmer it will appear next to a lesser-used pixel. In the case of LCDs, the physics of burn-in are different than plasma and OLED, which develop burn-in from luminance degradation of the light-emitting pixels. For LCDs, burn-in develops in some cases because pixels permanently lose their ability to return to their relaxed state after a continued static use profile. In most typical usage profiles, this image persistence in LCD is only transient. Both plasma-type and LCD-type displays exhibit a similar phenomenon called transient image persistence, which is similar to screen burn but is not permanent. In the case of plasma-type displays, transient image persistence is caused by charge build-up in the pixel cells (not cumulative luminance degradation as with burn-in), which can be seen sometimes when a bright image that was set against a dark background is replaced by a dark background only; this image retention is usually released once a typical-brightness image is displayed and does not inhibit the display's typical viewing image quality.
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