Sep 24, Image Sticking in LCD TV Sets

Many are aware that if you leave a static image for a prolonged period on a plasma TV, you may 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.

LCD TVs do not suffer from burn-in, yet surprising as it may seem, they still suffer from image retention when a static or semi-static image is left displayed on the screen for too long.

The intensity of image retention depends on various factors, not just the duration the static image remains displayed 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 in the LCD industry as 'image sticking'. As with burn-in, image sticking 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.

It should be remarked that though burn-in in plasma televisions and image sticking in LCD display panels both result in image retention or ghosting on the display panel, yet burn-in and image sticking are two different phenomena.

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 display panel when a static image remains displayed on the screen for too long.

This results in a parasitic charge build-up, or polarization, within individual pixels and sub-pixels. This polarization takes place at the liquid crystal level in the LCD panel; it affects the crystals' optical properties  as it prevents the liquid crystals to return 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 sticking would - as pointed out above - vary among different brands, and depends on several factors including operating temperature, time the static image remained on, and the image pattern, contrast and brightness levels.

Unlike permanent burn-in in phosphor-based displays, which is the result of a premature 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 sticking can be reversed depends on the severity of the causes that eventually led to image retention; top in the list is the environmental temperature at which image sticking took place.

A way to remove a retained image 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-back 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, yet our best advice is to follow the manufacturer's instructions - if available.

Generally, manufactures do not warrant an LCD display device against the occurrence of image retention.

Both burn-in and image sticking are considered by 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 image retention is end-user dependent.

The best way to avoid image sticking 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 semi-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, try not to pause a picture on your LCD TV 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. True that a few minutes in this state would not do any harm, but what if you forgot all about your TV after having say answered a phone call?

Finally, you should always power down the display panel during those periods of inactivity.

Surely, working with a retained image in the background is to say the least, extremely annoying.  And as expressed earlier on, manufactures' warranties would not generally cover image-sticking issues with LCD panels.

However, to put this whole discussion in the right perspective, it is important to keep in mind that the need to display a static image for more than a few minutes in home entertainment is generally non-existent. Even more significant is the fact that, the probability you would experience image sticking after a fixed image has been displayed on an LCD panel for say a few hours is still remote.

Generally, you would need more than just a few hours for this to happen under the typical home environment. Just look at the many LCD monitors in use with today's PCs in the home; these generally display static or semi-static images for prolonged periods without ever having issue with image sticking.

At the same time, you cannot really tell how long you have to wait for image sticking to take place - so the risk is always there.

Our recommendation is to activate a screen saver during periods of prolonged non-use; this should not be a problem especially if your LCD screen is PC driven. Alternatively, switch your LCD TV off; it is best for your LCD screen and for your electricity bill.

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