Phosphor burn-in

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Phosphor burn-in seen at Melbourne Airport. The TV set usually cycles its display between a small number of stills of information, which remain visible, even when the display is switched off, as overlaid burnt-in images.

Phosphor burn-in is a permanent disfigurement of areas on a cathode ray tube (e.g. a computer monitor or TV screen) caused by still images being displayed continuously for long periods.

1 Causes of burn-in
2 Prevention
3 References
4 External Images

[edit] Causes of burn-in

With phosphor-based electronic displays (including cathode-ray type computer monitors and plasma displays), the prolonged display of a menu bar or other graphical elements over time can create a permanent ghost-like image of these objects. This is due to the fact that the phosphor compounds which emit the light lose their luminosity with use. As a result, when certain areas of the display are used more frequently than others, over time the lower luminosity areas become visible to the naked eye and the result is called burn-in. While a ghost image is the most noticeable effect, a more common result is that the image quality will continuously and gradually decline as luminosity variations develop over time... resulting in a "muddy" looking picture image.

The burn-in problem can become even more pronounced with plasma displays because of the discrete nature of the pixel elements. Some display manufacturers include image rotation or other mechanisms to reduce the rate of burn-in. One manufacturer has introduced a technology called ZeroBurn(R) which can eliminate it altogether.

Plasma displays also exhibit another image retention issue which is sometimes confused with burn-in damage. In this mode, when a group of pixels are run at high brightness (when displaying white, for example) for an extended period of time, a charge build-up in the pixel structure occurs and a ghost image can be seen. However, unlike burn-in, this charge build-up is transient and self corrects after the display has been powered off for a long enough period of time, or after running random broadcast TV type content.

LCD type displays exhibit a similar phenomenon, although the mechanics of the image retention are different. In the case of LCD displays, the liquid crystal molecules which convert the white backlight to color as it passes through the membrane lose their rotation elasticity. In this case they are unable to fully return to their normal rotation state. As in the case with plasma displays, this is usually transient and will self correct after a period of off time or dynamic content. However, in severe cases it can become permanent.

[edit] Prevention

The development of screensavers was intended to reduce the effects of phosphor burn-in by automatically generating random content on the display after a period of inactivity. Screensavers achieve this by generating a constantly changing image to ensure that every pixel in the display is being used at approximately the same rate as the others. While screensavers such as this reduce the rate of burn-in, they do not eliminate it.

Another method for reducing the rate of burn-in on plasma displays is the inclusion by manufacturers of image-rotation features which periodically move the image around a five to ten pixel radius. While this helps distribute the luminosity degradation a little, it does nothing to solve the root problem.