Screen Uniformity Test

In short Uniformity is whether the panel is equally bright and equally neutral across its whole area, and the fault it reveals has a name: the dirty screen effect. It looks like smears or blotches that do not wipe off, and it is most visible on flat mid-grey and during panning shots in sport — which is where most people first notice it, watching a football pitch move across the screen. It is a manufacturing variation rather than a defect, present to some degree on nearly every large panel, and larger panels are worse because keeping a backlight even across a metre is harder than across 24 inches. Mid grey shows it best, followed by cyan; pure white hides it almost entirely, which is why a quick check on a white field tells you nothing. Judge it fullscreen at your normal brightness and step back a metre or two, because uniformity is a whole-panel judgement and standing close to a large screen shows you one region at a time.