Image persistence, or image retention, is a phenomenon in LCD and

plasma display A plasma display panel is a type of flat-panel display that uses small cells containing Plasma (physics), plasma: Ionization, ionized gas that responds to electric fields. Plasma televisions were the first large (over diagonal) flat-panel displ ...

s where unwanted visual information is shown which corresponds to a previous state of the display. It is the flat-panel equivalent of screen burn-in. Unlike screen burn-in, the effects are usually temporary and often not visible without close inspection. Plasma displays experiencing severe image persistence can result in screen burn-in instead. Image persistence can occur as easily as having something remain unchanged on the screen in the same location for a duration of even 10 minutes, such as a web page or document. Minor cases of image persistence are generally only visible when looking at darker areas on the screen, and usually invisible to the eye during ordinary computer use.

Cause

Liquid crystal Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal can flow like a liquid, but its molecules may be oriented in a common direction as i ...

s have a natural relaxed state. When a

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

is applied they rearrange themselves to block certain

light wave In physics, electromagnetic radiation (EMR) is a self-propagating wave of the electromagnetic field that carries momentum and radiant energy through space. It encompasses a broad spectrum, classified by frequency or its inverse, wavelength, ra ...

s. If left with the same voltage for an extended period of time (e.g. displaying a pointer or a taskbar in one place, or showing a picture for an extended period of time), 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 (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...

off by a slight degree, which causes the image to look like the traditional "burn-in" on phosphor based displays. The cause of LCD image retention is different from phosphor aging as in CRTs, but the visual phenomenon is the same: uneven use of display pixels. Slight LCD image retention can be recovered. When severe image retention occurs, the liquid crystal molecules have been polarized and cannot rotate in the electric field, so they cannot be recovered. The cause of this tendency is unclear. It might be due to various factors, including accumulation of ionic impurities inside the LCD, impurities introduced during the fabrication of the LCD, imperfect driver settings, electric charge building up near the electrodes,

parasitic capacitance Parasitic capacitance or stray capacitance is the unavoidable and usually unwanted capacitance that exists between the parts of an electronic component or circuit simply because of their proximity to each other. When two electrical conductors a ...

, or a DC voltage component that occurs unavoidably in some display pixels owing to anisotropy in the dielectric constant of the liquid crystal.

Prevention and treatment

Image persistence can be reversed by allowing the liquid crystals to relax and return to their relaxed state, such as by turning off the monitor for a sufficiently long period of time (at least a few hours). For most minor cases, simply continuing to use the computer as usual (and thus allowing other colors to "cover" the affected regions) or turning off the monitor for the night is more than enough. One strategy for users looking to avoid image persistence artifacts is to vary the activities performed on a computer to avoid static colors and hide elements on the screen which are displayed perpetually (such as an OS's Taskbar). Another strategy is the usage of a

screensaver A screensaver (or screen saver) is a computer program that blanks the display screen or fills it with moving images or patterns when the computer has been idle for a designated time. The original purpose of screensavers was to prevent phosphor s ...

to help during times the computer is left unattended. Covering the entire display area with pure white for an extended period of time is also a useful proactive solution.

References

External links

Article on LCD image persistence
{{Webarchive, url=https://web.archive.org/web/20051211013238/http://compreviews.about.com/od/monitors/a/LCDBurnIn.htm , date=2005-12-11
TFT LCD Burn-in
Display technology Liquid crystal displays