What to look for on each colour
| Colour | Reveals |
|---|---|
| Black | Stuck pixels appear as bright coloured dots. Also shows backlight bleed as lighter patches at the edges and corners. |
| White | Dead pixels appear as black dots. Also reveals clouding, a grey mottled unevenness across the panel. |
| Red, green, blue | Individual subpixel failures. A pixel can fail in one channel only, which shows up on that colour and nowhere else. |
| Grey | Banding and brightness uniformity. Gradients should look smooth, not stepped. |
Clean the screen first. A speck of dust looks exactly like a dead pixel on a white field. Wipe the panel with a dry microfibre cloth before you start, or you will find faults that are not there.
Buying a used monitor or laptop
This test takes under a minute and is worth running before money changes hands. On a used laptop, pair it with the keyboard test and mouse test, which catch the other two expensive faults. Load the page on the seller's machine, run through the sequence, and photograph anything you find. Pay particular attention to the black and white fields, since those catch the two most common defects. Backlight bleed on a black screen is easy to miss in a bright room, so cup your hands around the edges of the display or dim the lights.
Stuck pixels sometimes recover
A stuck pixel is powered but frozen on one value, and rapidly cycling colours over it can occasionally shake it loose. Leave the colour sequence running for ten to twenty minutes and check again. Very light pressure through a soft cloth while the screen is on also works sometimes. Do not press hard: the pressure can spread the damage permanently, and a single stuck pixel is a much better outcome than a cracked panel.
Other checks
Common questions
What is the difference between a dead and a stuck pixel?
A dead pixel receives no power and stays black on every colour. A stuck pixel is permanently on in one colour, so it shows as a bright red, green or blue dot on a black background. Stuck pixels sometimes recover; dead ones do not.
Can a stuck pixel be fixed?
Sometimes. Rapidly cycling colours over the area can unstick it, and very gentle pressure with a soft cloth while the screen is on occasionally works. Neither is guaranteed and pressing hard can cause permanent damage.
How many dead pixels before a warranty claim?
Manufacturers set thresholds under the ISO 9241-307 standard and most consumer panels are allowed several defects before qualifying for replacement. Check your specific manufacturer's policy, and photograph what you find.
Why check a screen with white and grey?
A full white field reveals backlight bleed and clouding around the edges, which is common on IPS panels. Mid-grey shows banding and uneven brightness that solid colours hide.