Image persistence is the LCD and plasma display

Plasma display

A plasma display panel is a type of flat panel display common to large TV displays or larger. They are called "plasma" displays because the technology utilizes small cells containing electrically charged ionized gases, or what are in essence chambers more commonly known as fluorescent...

 equivalent of screen burn. Unlike screen burn, however, the effects are usually temporary. Plasma displays can also suffer from burn-in.

Cause

Liquid crystal

Liquid crystal

Liquid crystals are a state of matter that have properties between those of a conventional liquid and those of a solid crystal. For instance, an LC may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of LC phases, which can be...

s have a natural relaxed state. When a voltage

Voltage

Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...

 is applied they rearrange themselves to block certain light waves. If left with the same voltage for an extended period of time (e.g. displaying a mouse cursor or the Microsoft Windows

Microsoft Windows

Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...

 Taskbar

Taskbar

In computing, a taskbar is a bar displayed on a full edge of a GUI desktop that is used to launch and monitor running applications. Microsoft incorporated a taskbar in Windows 95 and it has been a defining aspect of Microsoft Windows's graphical user interface ever since. Some desktop environments,...

 in one place), the liquid crystals can develop a tendency to stay in one position. This ever so slight tendency to stay arranged in one position can throw the requested color

Color

Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...

 off by a slight degree, which causes the image to look like the traditional "burn-in" on phosphor based display

Phosphor burn-in

Screen burn-in, image burn-in or ghost image, colloquially known as screen burn or screen afterimage, is a permanent discoloration of areas on an electronic display such as a cathode ray tube display or computer display monitor or Television set caused by cumulative non-uniform usage of the...

s. In fact, the root cause of LCD image persistence is the same as phosphor burn-in, namely, non-uniform usage of the display's pixels.

The cause of this tendency is unclear. It might be due to accumulation of ionic impurities inside the LCD, electric charge building up near the electrodes, parasitic capacitance

Parasitic capacitance

In electrical circuits, parasitic capacitance, stray capacitance or, when relevant, self-capacitance , is an unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other...

, or "a DC

Direct current

Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...

 voltage component that occurs unavoidably in some display pixels owing to anisotropy in the dielectric constant of the liquid crystal".

Usually the image persistence is temporary, but can become permanent. As a result, all major LCD display manufacturers exclude image persistence from their warranties.

Prevention/treatment

Image persistence can usually be reversed by allowing the liquid crystals to return to their relaxed state. In other words, turning off an LCD display for hours or days will relax the crystals and eliminate the image retention. For PC monitors, it is also ideal to rotate desktops

Desktop environment

In graphical computing, a desktop environment commonly refers to a style of graphical user interface derived from the desktop metaphor that is seen on most modern personal computers. These GUIs help the user in easily accessing, configuring, and modifying many important and frequently accessed...

, and hide away elements on the screen which normally would be displayed perpetually (like the taskbar in Microsoft Windows or the Dock in Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

). The usage of a screensaver

Screensaver

A screensaver is a type of computer program initially designed to prevent phosphor burn-in on CRT and plasma computer monitors by blanking the screen or filling it with moving images or patterns when the computer is not in use...

that has a constantly changing image can help as well.

Another approach to removing LCD image persistence is to first create a solid white image and display the image as a screensaver covering the entire display area for an extended period of time.http://docs.info.apple.com/article.html?artnum=88343

External links

• Article on LCD Image Persistence