How to Find a Dead Pixel (and Tell It From Dust)
Check any screen with a full-screen colour cycle, work out whether the dot is dead, stuck or just dirt, and see how many faults your warranty covers.
The first dead pixel I ever found turned out to be a crumb.
I spent a good ten minutes squinting at a new monitor, filled in the warranty form, and then wiped the screen while waiting for a reply. It came off on the cloth. So before anything else: find a dry microfibre cloth and clean the panel. On a white background a speck of dust is indistinguishable from a pixel that never lights, and support desks see that mistake all day long.
Once the screen is clean, the Dead Pixel Test fills your whole display with one flat colour at a time. That is the entire trick. A broken pixel is a single dot among two million or more, and it only becomes visible when everything around it is uniform.
One colour will not do it
Every pixel on an LCD is three subpixels side by side: red, green, blue. Mix them and you get the colour you asked for. Freeze one and you get a tint that follows the pixel around forever.
The catch is that a frozen subpixel hides on its own primary. A red subpixel stuck at full brightness vanishes completely on a red field, and on a green one it sits there like a tiny lamp. That is why the test runs the primaries separately, then black to catch anything glowing when it should be off, then white to catch anything dark when it should be lit. Yellow, cyan and magenta come last, because a subpixel that has gone dim rather than fully dead shows up best on a mixed field.
Nine colours, maybe forty seconds of clicking. Sit about 40 cm back and let your eyes travel across the panel instead of locking onto the middle — peripheral vision is surprisingly good at spotting a dot that does not belong.
Dead, stuck, or neither
Three questions sort out almost every case.
Did the dot light up on black but blend into white? Something is holding it on. That is a bright pixel, and it is the type that occasionally recovers.
Did it stay dark on white but disappear on black? The transistor driving it is open-circuit. No software will bring that back.
Did it look exactly the same on black, white, red and green? Then it is not a pixel at all. It is sitting on top of the glass: dust, a fingerprint, a dried water spot, or a scratch in the anti-glare coating. Pixel faults change with the background. Dirt does not.
The tool asks those three questions as checkboxes and names the fault for you, which saves arguing with yourself about what you just saw.
What the warranty actually promises
Here is the part nobody reads until they need it. Screens are graded under ISO 9241-307, and almost everything sold to consumers is Class II. Class II permits two permanently lit pixels, two permanently dark pixels and five stuck subpixels per million pixels.
Run that on a 1080p monitor, 2.07 megapixels, and you get 4 bright, 4 dark, 10 subpixels. On a 4K panel it is 16, 16 and 41. Your single annoying dot is, by the standard, a working screen.
Manufacturers sometimes go further than the standard on purpose. Dell’s Premium Panel Guarantee covers a single bright pixel on much of the UltraSharp line, which is a genuinely better deal than the spec sheet implies. Check your model’s warranty page before you give up.
Worth one attempt
For a stuck pixel, flashing is the only home remedy with any track record. The tool’s flash mode cycles the cell between full brightness and black about five times a second; leave it for fifteen or twenty minutes. Some people add light pressure with a soft cloth directly over the spot while it runs. Light pressure. Push hard and you will trade one stuck pixel for a bruise-shaped patch of them.
It works sometimes. More often it does not, and then you are back to the warranty table.
If you are testing a second-hand monitor before handing over cash, do this first and check the screen resolution and keyboard while you are at it. Open the Dead Pixel Test and run the cycle — it takes less time than reading this did.