One of the major problems with old CRT displays was burn-ins, where after a length of displaying the same image or pattern on the screen, a shadow of that image would persist even when the image had changed. With modern LCD displays, you might experience an image persistence problem that's similar to the classic burn-in, and in addition you may also experience stuck and dead pixels.
While classic burn-ins usually happen on displays over long periods of time as the phosphors in the screen's front panel break down, LCDs are immune from this because the image crystals and backlight are separate. However, they do suffer from "image persistence," where a constant voltage will cause the crystal voltage-response curve to change, resulting in them letting more or less backlight through for a given voltage than when compared with surrounding pixels.
This usually happens over extended periods of time, but can also happen in short times of what would normally be considered "standard use." For instance, one user who posted in this Apple discussion thread had the Time Machine restore window burn in on his iMac LCD after being up for just a number of hours.
Luckily, unlike CRT burn-ins, image persistence is usually rare and reversible; however, if your monitor is regularly retaining image patterns, we recommend you get the monitor serviced and/or replaced.
In addition to burn ins, LCDs can also get stuck pixels, where one or more of the three red, green, or blue colors in the pixel loses the ability to change intensity, resulting in a persistent color regardless of the signal being given to the pixel. If all three colors are stuck, the pixel will appear more prominently than if only one is stuck, but in all cases the pixel will be noticeable, especially if it's toward the center of the display (unfortunately, fate usually has it that a stuck pixel on your display will be right in the center).
Similar to stuck pixels, dead pixels are when one or more color components of a pixel are not working. Unlike stuck pixels, no voltage is getting to the pixel components, which results in a black dot for the affected components. This can cause a pixel to appear slightly red, blue, or green, depending on which pixels are affected.
The easiest way to check for stuck or dead pixels is to run a white background over suspected areas of your display, and if you see a black dot then the pixel is dead. If the dot is colored then you're most likely dealing with a stuck pixel. To further test the situation, run pure red, blue, and green images over the area of your display to see if a pixel is not changing. If you see a black dot for any color, then that color component is dead for the pixel, but if the pixel is colored differently for any or all of the colors and does not show black, then the pixel is stuck for the respective color component(s).
Whenever these problems happen, there are a few things you can try to fix the issue. Some give a higher yield of success than others, but some can also be potentially dangerous to your display so while we will mention them here, we caution you when proceeding with them.
For LCD image persistence, you can try resetting the pixel response curves by first turning off the display for a few minutes. The longer the display is off, the more probable it is the pixels have cooled and equilibrated to their baseline "off" state. After this, turning all pixel color components fully on for an extended period will equilibrate them to their full brightness again. The best procedure for doing this in OS X is to create a pure white image by opening up a blank document and using the screen-capture hot keys, "Cmd-Shift-4" (note we're using "4" and not "3"), and then selecting an area of white on the screen. Then place the image from the desktop in its own folder and select that folder for use with the pictures screen saver, ensuring the screensaver options are set to not pan or otherwise display boarders or background colors. Then use the energy saver system preferences to disable both the display and system sleep, and finally start the screensaver (hot-corners are useful for this).
With the screensaver active, turn off the display and let it cool down as mentioned above. Then turn it on and let it warm up (you can adjust the brightness to any level that's comfortable for you, since the backlights have nothing to do with the pixel response and image persistence problems). Run the display like this for at least as long as you displayed the original pattern that caused the image persistence, but it wont hurt to run it for longer. With this setup, the pixels should slowly re-equilibrate.
For stuck pixels, there are a variety of fixes that can help. The first and least intrusive is the use of a program that exercises the pixels. The popular "jscreenfix" program is a Java applet that will run a rapid pattern over a stuck pixel and exercise it to hopefully clear the problem. This can also be used for dead pixels as well, so download and try the program out (sometimes it can take a long time for pixels to unstick). Other programs you can use to test pixels are LCDtest, Pixel Fix, and Dead Pixel Tester.
If jscreenfix does not work, you can try various pressure remedies. We caution using this, since you can further damage your screen, but if you are aware of the risk, this has helped a few people clear stuck and dead pixels. The idea is that the liquid in the liquid-crystal may have shifted and is not getting full electrical contact, or another connection is slightly ajar from its settings, which can sometimes be fixed by massaging the components of the display. There are a variety of approaches to this, which include tapping, rubbing, and pressing on or around the dead/stuck pixels. A few of these methods are outlined in detail in this wikiHow article. Again, we caution the use of these methods, especially if your system is under warranty, in which case we recommend you first talk to Apple.
NOTE: Pressure methods will not work on any glossy LCD, since you have a layer of glass in front of the display and you risk cracking it if you put pressure on it. You may get away with gentle rubbing, but it will not hold up to firm pressure.
The key to preventing image persistence is to frequently run a screensaver that exercises the pixels, and couple this with frequently turning off your display. While general use of the system will usually ensure that the working area of the display is constantly changing intensity, items like the menu bar and dock may be presented enough to potentially cause image persistence. Dimming the display used to help prolong the life of CRT monitors because it cut down on the radiation output that caused the phosphor breakdown, but for LCDs the backlight intensity will not affect the pixels. As such, you can safely run your LCD monitor at any brightness without increasing the potential of image persistence.
These preventative practices may also help prevent dead and stuck pixels from occurring.
Major Hardware Failures:
Beyond pixel-related problems such as these, LCD monitors can experiences several severe hardware failures that are quite apparent. The first is if the backlights go out, which can be caused by broken backlight tubes or a broken inverter board for the display. When this happens, you will see uneven brightness or the inability to light your display. You can check for pixel functionality by holding a bright light up to the display and you should see a faint image of the pixels on the screen. This can sometimes be repaired by replacing the inverter board on the display.
The last problem is a leak of the liquid crystal. This will look like a dark oil blot on the display that may grow slowly or suddenly appear. If this happens, the display panel will need to be replaced.Resources