Dead pixel test
In fullscreen, the arrow keys and space change colour. Press Escape to leave.
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Fills the screen with solid colours in turn, which is the only reliable way to spot a dead or stuck pixel — against a plain field a single wrong dot is unmissable, and against normal content it is invisible.
How to use the dead pixel test
The distinction worth knowing is between dead and stuck. A dead pixel receives no power and stays black on every colour, so it shows up against white and vanishes against black. A stuck pixel is jammed at one subpixel value and shows as a coloured dot — red, green or blue — that stays the same colour whatever the screen displays. Cycling through white, black and the primaries catches both, which is why the sequence matters more than any single screen.
Stuck pixels sometimes recover. Rapidly cycling colours over the affected area for a few minutes can unstick one, and gentle pressure with a soft cloth while the screen is on works often enough to be worth trying. Dead pixels do not recover — no amount of cycling restores a pixel that is not receiving power.
Worth knowing before contacting a manufacturer: almost none will replace a panel for a single dead pixel. The ISO 9241-307 standard defines classes, and most consumer monitors ship to Class II, which permits a small number of defective pixels — commonly two full and five subpixel faults per million. Check the specific policy before assuming a warranty claim, because the answer is usually that the panel is within specification.
One caution: what looks like a dead pixel is often dust on the screen. Wipe it first.
Questions
A dead pixel gets no power and stays black on everything. A stuck pixel is jammed at one colour. Cycling all the colours catches both.