One of the problems with CRT monitors over time was a condition called burn-in. This resulted in an imprint of a image onto the display that was permanent. It was caused from the continuous display of a particular image on the screen for extended periods of time. This would cause a breakdown in the phosphors on the CRT and would result in the image being burned into the screen, hence the term burn-in.
LCD monitors use a very different method for producing the image on the screen and are supposed to be immune to this burn in effect. Rather than phosphors being used to generate the light and color, an LCD has a white light behind the screen and then uses polarizers and crystals to filter the light to specific colors. While LCDs are not susceptible to the burn-in the same way CRT monitors are, they do suffer from what the manufacturers like to call image persistence.
What is Image Persistence?
Like the burn-in on CRTs, image persistence on LCD monitors is caused by the continuous display of static graphics on the screen for extended periods of time. What this does is cause the LCD crystals to have a memory for their location in order to generate the colors of that graphic. When a different color is then displayed in that location, the color will be off from what it should be and instead have a faint image of what was previously displayed.
The persistence is the result of the how the crystals in the display work. Essentially, the crystals move from a position that allows all light to go through to another that allows none through. Its almost like a shutter on a window. When the screen displays an image for an extremely long time, the crystals can want to stich in a certain position, similar to a window shutter. It may shift a bit to alter the color but not completely resulting in it moving to the position it is really being asked to.
This problem is most common for elements of the display that do not change. So items that are likely to generate a persistent image are the task bar, desktop icons and even background images. All of these tend to be static in their location and will be displayed on the screen for extended period of time. Once other graphics are loaded over these locations, it may be possible to see a faint outline or image of the previous graphic.
Is it permanent?
In most cases, no. The crystals do have a natural state and can shift depending upon the amount of current used to generate the desired color. As long as these colors do shift periodically, the crystals at that pixel should fluctuate enough such that the image will not be permanently imprinted into the crystals. Having said that, it is possible that the crystals could get a permanent memory if the screen image does not change at all and the screen is left on all the time. It is very unlikely for a consumer to have this happen as it is more likely to happen in a fixed display such as those seen as display boards for businesses that do not change.
Can it be prevented/corrected?
Yes, image persistence on LCD screens can be corrected in most cases and is easily prevented. Prevention of image persistence can be done through some of the following methods:
- Set the screen to turn off after a few minutes of screen idle time under the display and screen preferences in the operating system. Turning the monitor display off will prevent an image from being displayed on the screen for extended periods of time. Of course, this could be annoying to some people as the screen may go off more than they wish. Even setting it to do this when idle for fifteen to thirty minutes can make a huge difference.
- Use a screen saver that either rotates, has moving graphic images or is blank. This also prevents an image for being displayed in screen for too long.
- Rotate any background images on the desktop. Background images are one of the most common causes for image persistence. By switching backgrounds every day or few days, it should reduce the chance of persistence.
- Turn off the monitor when the system is not in use. This will prevent any problems where the screen saver or power function fails to turn off the screen and result in an image sitting on the screen for long times.
Using these items can help prevent the image persistence problem from cropping up on a monitor. But what if the monitor is already displaying some image persistence problems? Here are a few steps that can be used to try and correct it:
- Turn off the monitor for extended periods of time. It can be as little as several hours or it could be as long as several days.
- Use a screen saver with a rotating image and run it for an extend periods of time. (This is done by setting a rotating screen saver and disabling the monitor sleep setting.) The rotating color palette should help remove the persistent image but it could take a while to remove it.
- Run the screen with a single solid color or bright white for an extended period of time. This will cause all of the crystals to be reset at a single color setting and should erase any previous image persistence.
Going back to the window shutter analogy, these steps are very similar to essentially wiggling the window shutter to eventually get it unstuck so that it can fully articulate again to give you any level of desired light to pass through.
While LCDs don't have the same burn-in problem that affected CRTs, the image persistence problem could come about. Hopefully this article has addressed what the issue is, what causes it, how to prevent it and how to correct it. With all the preventative steps in place, a user should never really have to encounter this problem.