LCD screens have often shown some backlight non-uniformity (called mura), because an LCD panel can let the backlight leak through more in certain spots than in others. Normally, this appears as an uneven cloudiness that usually can be seen only when the screen image is dark or completely black. But as TVs get ever thinner, we've seen a new problem that can cause even more noticeable type of non-uniformity, which, at its worst, can be distracting even in bright scenes.
For several years, both plasma and, especially, LCD TVs with LED backlights have been getting thinner and thinner as bezels and frames shrink, resulting in aesthetically pleasing, super-slim, borderless TVs. The new type of non-uniformity is caused by the LCD panel getting pinched and contorted by the cabinet assembly and producing bright patches of illumination, typically around the borders of the panel.
A bright patch often appears only in the corners of the display as a faint "spotlight" effect and is only really noticeable during very dark scenes or when you're watching a movie with black bars on the top and bottom of the image. But our lab testers have seen this issue getting worse. At times, even large sections of the screen look noticeably brighter then the rest.
The other problem with non-uniformity is how inconsistent it can be. The intensity and number of bright spots can vary substantially between different samples of the same TV, since the effect depends on how the individual model was assembled. This makes it difficult to predict how a given TV will look.
So when you bring home your new LCD TV, especially a slim one with LED backlighting, be sure to play some dark-scene content or pause on a black frame between commercials or during credits to see if your TV has any cloudiness or bright patches. If you're distracted by them, you may want to exchange it for another TV.
