The entire surface of a LCD panel is backlit from behind by a light source (CCFL or LED) and the LCD blocks out the light that is not needed when displaying a particular image. Backlight bleeding most commonly occurs when this light is not 100% blocked, allowing excess light to "bleed" around the edges of the LCD panel. This backlight bleeding issue leaves spots of lighter areas on a dark or black background.
Unfortunately, many LCD monitors suffer from at least a small amount of backlight bleed because the opacity of LCD panels and construction materials used in the monitor manufacturing process are not high enough to completely block all light. This will usually only cause problems if the backlight bleeding can be easily detected by the human eye. The graphic to the right shows an example of what an LCD display with excessive backlight bleeding looks like with a dark, static background. As you can see, the top left and bottom right corner are lighter in color than the center of the display.
Fixing Backlight Bleed
In general, there is no definite fix for backlight bleeding other than completely dismantling the monitor and adding extra light blocking materials (such as black electrical tape) around the LCD panel. Some users in this hardforum.com thread have had success improving the level of bleed on the model 2005FPW Dell LCD using the method listed. Note: Dismantling of a LCD monitor in an attempt to reduce backlight bleed should be done at your own risk and only as a last resort if the monitor is no longer under warranty and can't be returned or exchanged.
The best way to "fix" backlight bleed is to have the monitor exchanged if the retailer will allow it and take your chances with a new LCD panel, hopefully one with less bleed. The ideal solution is to do your homework and in the future avoid monitors with a history of backlight bleeding and other quality control issues.
How To Avoid Backlight Bleed When Buying A New Monitor
Read reviews on the model of LCD display you plan on purchasing beforehand and look for any complaints about backlight bleeding. Buy from a retailer that will allow you to exchange the display if there are any major problems and, if possible, try to view a display model or two before making a purchase. You should also avoid LCD monitors from brands which are known to have quality control problems, as they will be much more prone to display inconsistencies such as backlight bleeding.
Even this does not guarantee you will receive an LCD completely free from bleeding, but it can limit the chances and give you a higher success rate.