Mura is an effect that looks like clouds on a liquid crystal display (LCD). Often, these clouds are visible against a dark screen, usually when the screen is viewed off-centre. Mura is surprisingly common, although this is of little consolation to owners of displays with this problem. The cause is related to a few issues and is often not completely repairable, short of replacing internal screen components.
A lack of consistency in the television's processor when controlling the colour intensity from one part of the screen to another results in mura. This is a calibration error, developed at the factory. This is normally not adjustable and instead involves the repair or replacement of key internal electronics to possibly remedy.
Mounting the screen panel with improper pressure effectively crushes certain picture elements (pixels), causing them to display whiter than the background. This usually manifests at screen corners or anywhere the screen is connected to the chassis of the unit. Occasionally, loosening the screws that mount the panel remedies this issue, but this must be performed by qualified repair personnel.
Cell gap mura results from improper manufacturing. Each LCD cell must be of identical size. If one is larger than the others, it will produce more light than its neighbours. If it's smaller, it will appear darker. These anomalies are recognised as light and dark mura, respectively. In addition, they are introduced from impurities such as chemicals and dust making their way onto the panel during the manufacturing process.
The backlight on an LCD is either a fluorescent-based matrix or a light-emitting diode array. In either case, variations in backlight intensity can result in light shining "through" the screen, brighter than in other areas. This is often reduced by backing down the backlight control in the user adjustment menu, although this usually only mitigates the problem without completely solving it.