Image Sticking in LCD and LED HDTVs
Is this a problem?
Isn't image retention just an issue with Plasma TVs?
Image sticking is surely one of the least known phenomena associated with the use of TFT LCD panels. Yet, despite what many may believe, image retention—or ghosting—is not just an issue with plasma televisions.
In this short LCD TV guide, we explain what causes image retention in LCD TVs and show you what you can do to avoid it.
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Many are aware that if you leave a static image for a prolonged period of time on a plasma TV, you risk phosphor burn-in. The result is that once you remove the static image, you would still be able to see a faint outline—or ghosting—of the original image, even when you change the picture content.
CCFL and LED LCD TVs do not suffer from burn-in, yet they may still suffer from image retention when a static or semi-static image is displayed on the screen for too long. The intensity of image retention depends on various factors, not just the duration the image remains on the screen. Issues such as image makeup, operating temperature, and the LCD panel brand itself, should also be factored in.
Image retention in LCD panels is often referred to in the LCD industry as 'image sticking'. As with burn-in, image retention is a phenomenon where a faint outline of a previously displayed fixed or semi-fixed image remains visible on the screen even when the image is changed.
Note that though burn-in in plasma TVs and image sticking in LCD displays both result in image retention or ghosting, yet burn-in and image sticking are two different phenomena.
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What Causes Image Retention in LCD Displays?
Image sticking is an intrinsic behavior of TFT LCD panels. It is the result of their susceptibility to polarization of the liquid crystals inside the LCD display panel when a static image remains displayed on the screen for too long.
This results in parasitic charge (polarization) build-up within individual pixels and sub-pixels at the liquid crystal level in the LCD panel; it affects the display optical properties as it prevents the crystals from returning fully to their normal 'relaxed' state upon deactivation.
More specifically, the result is a 'retained pixel charge'. This can affect the crystal alignment at the bottom or top of a liquid crystal cell, or even migration to the edges of a cell, depending on the resultant polarity of the parasitic charge buildup. These conditions may cause image sticking over an entire area of the screen, and in particular over those boundaries where there are distinct color changes.
The severity of the resultant image retention would as pointed out above, vary among different brands, and depends on several factors including:
- An operating temperature that is out of the recommended operating temperature range,
- time the static image remained on—the longer the static image is on the worst the image sticking effect, and
- image build up—including the image pattern itself as well as image contrast and brightness levels.
Unlike permanent burn-in in phosphor-based displays, which is the result of a premature and permanent aging of the phosphors of individual pixels, and thus, is irreversible, image sticking in LCD panels can often be reversed to a point of total invisibility.
However, the extent to which image retention can be reversed depends on the severity of the causes that led to image retention; top in the list is the environmental temperature at which image sticking took place.
A way to remove a retained retention on an LCD panel is to run an all-white screen saver for several hours. It would generally help to run this image sticking reversal operation at an elevated temperature of around 100 deg. Fahrenheit or 40 deg. Celsius. This should help speed up the reversal process.
Some manufactures recommend using an all-black or dark gray pattern screen saver instead of an all-white screen. Whichever method you choose, make sure the LCD TV or monitor energy savings settings will not turn the backlight off after some time of inactivity. Other manufacturers recommend turning off the LCD display for a longer period than the time it took for the static image to cause image retention.
While all three methods can help remove image sticking, our best advice is to follow the manufacturer's instructions when available.
Generally, manufactures do not warrant an LCD display device against the occurrence of image retention. Both burn-in in plasma displays and image retention in LCD panels are considered by display manufactures as phenomena that are inherent to the respective phosphor-based (CRT and Plasma TVs) and LCD display technologies. Furthermore, their occurrence is tied up to their end-use and as such, the possibility of an LCD display developing image retention is end-user dependent.
The best way to avoid image sticking in the first place is to prevent the prolonged presentation of static images on the screen.
Try not to display the same static image on an LCD panel for more than 2 hours when working at normal ambient temperature. However, some manufactures recommend reducing this to as little as 30 minutes when working in an elevated temperature environment (above 95 deg. Fahrenheit or 35 deg. Celsius). Make use of a dynamically changing screen saver and adjust its settings accordingly.
In home entertainment applications, many do not realize that prolonged presentation of those vertical or horizontal gray or black bars, say when viewing 4:3 program content over a wide-screen LCD panel, is also a form of static image. These should be avoided by choosing an aspect ratio or zoom setting that expands the image to fill the whole screen area.
Similarly, avoid pausing a picture on your LCD TV screen for too long, nor allow station logos, program menus, etc., to remain still on the screen for an extended period. If for some reason, you need to pause a film or a show to do something else, it is better to turn off your LCD TV set. It is true that a few minutes in this state would not do any harm, but what if you forget about your TV after say having answered a phone call?
Finally, you should always power down the display panel during periods of extended inactivity.