DevicedialDead pixel test
Dead pixel test
Each square fills the whole screen. Click or press โ for the next colour, Esc to come back. Look from about 40 cm and move your eyes slowly across the panel.
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Black dots on the white screen are dead pixels and never come back. Coloured dots on the black screen are stuck ones โ those sometimes recover after ten minutes of the flasher.
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- Screenโ
- Flash rateโ
- Time in testโ
Clean the screen before you start. On a black field, a speck of dust and a stuck pixel look identical.
One gear check a month
MonthlyOne thing a month worth measuring before it fails properly โ a mic that reset itself, a stick that drifts, a switch sending two clicks. Two sentences and the test.
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How do I check a screen for dead pixels?
The Devicedial dead pixel test fills the screen with nine solid colors so a faulty pixel has nowhere to hide. Clean the panel first with a dry microfiber cloth โ on a black field, dust, a dried droplet and a stuck pixel are indistinguishable, and most spots people report turn out to be the first two.
Then read the two fields that matter. On white, a dead pixel appears as a black dot: it is stuck off and never lights. On black, a stuck pixel appears as a bright red, green, blue or white dot, because one or more of its subpixels is stuck on.
The pure red, green and blue fields narrow it to a single subpixel. A pixel that vanishes on the green field but sits black on red has lost only its red subpixel, which is a fault the white field alone would never show you.
Each field is chosen for one job, and the order is deliberate. Work through them slowly, from about half an arm’s length, and look at the corners rather than the middle.
| Field | Hex | What it exposes |
|---|---|---|
| White | #ffffff | dead pixels as black dots; also every smear and speck of dust |
| Black | #000000 | stuck pixels as bright dots; backlight bleed and clouding at the edges |
| Red | #ff0000 | a dead red subpixel โ the pixel sits black while the field is lit |
| Green | #00ff00 | a dead green subpixel |
| Blue | #0000ff | a dead blue subpixel |
| Cyan | #00ffff | a red subpixel stuck on โ it shows as a white dot |
| Magenta | #ff00ff | a green subpixel stuck on |
| Yellow | #ffff00 | a blue subpixel stuck on |
| Gray | #808080 | panel uniformity, clouding and anything still on the glass |
A fault that appears on exactly one primary is a single subpixel, which is the most common defect and the least visible in normal use. A dot black on all three is a whole dead pixel.
The other screen checks are next door: screen resolution reports the pixel count these fields are covering, and the refresh rate test measures how often they are redrawn. If the panel is a laptop’s, the camera test is the other half of the same hardware check.
Frequently asked questions
Is it a dead pixel or a stuck pixel?
Look at it on two fields. A dot that is black on the white field is a dead pixel: it never lights, and it is usually permanent. A dot that glows red, green, blue or white on the black field is a stuck pixel, with one or more subpixels held on. Dead pixels look black, stuck pixels look colorful โ that is the whole test.
Can a stuck pixel be fixed?
Sometimes, and it costs nothing to try. Rapidly cycling colors under the stuck pixel exercises its subpixels and can release a transistor that has latched; leave it running for twenty minutes to an hour before giving up. Gentle pressure through a soft cloth while cycling helps some panels and damages others, so treat it as a last resort. Dead pixels do not come back.
How do I tell a dead pixel from dust?
Clean the screen first โ that is the whole answer, and it is why most reported dead pixels are not dead pixels. Dust and dried spray sit on the outside of the panel, so they shift against the image when you move your head; a pixel fault is inside the stack and never moves. Wipe with a dry microfiber cloth, then look again on the black field.
How many dead pixels before a warranty claim?
Fewer than most people expect, and it varies by brand. Panels are graded against a pixel fault class, and consumer monitors are commonly sold under one that tolerates a small number of whole bright or dark pixels plus a handful of single subpixel faults per million before the panel counts as defective. Count what each field reveals, then check the figure in your model’s warranty.
Why does the test need the full screen?
Because the browser’s own interface covers pixels, and the edges and corners are where panel faults cluster. A full-screen field also removes every reference point, which matters more than it sounds: on a partly covered screen the eye keeps finding contrast at the window border and skips the corners entirely. Press Escape to leave a field at any time.
Does this work on a phone or an OLED TV?
Yes, and the black field is more useful there. OLED pixels make their own light, so a dead one is genuinely black and obvious, while an LCD leaks a little backlight through it. On OLED the gray field is worth a long look too: uneven patches are early burn-in rather than pixel faults, and no amount of color cycling will clear them.
How the test works
The test paints one solid color at a time across the full screen through the Fullscreen API, with no
scaling, no image and nothing else drawn. Colors are specified at full intensity in hexadecimal
rather than by name, because the CSS keyword green is only half brightness (#008000); a weak
green subpixel would still light on it and pass. The primaries here are #ff0000, #00ff00 and
#0000ff, which drive one subpixel at a time to maximum.
The order runs white, black, the three primaries, the three secondaries and finally mid-gray, so the two fields that decide dead against stuck come first and the diagnostics follow. Nothing is measured automatically: a browser cannot read back what a panel emits, so the test presents the conditions and your eye does the detection. Nothing is uploaded and no image is captured.
Sources:
Why the color fields are the ones they are
A pixel is three subpixels. Red, green and blue sit side by side, and any of them can fail on its own. That is why a single white field is not a test: a pixel with a dead red subpixel still lights on white, just slightly cyan, and at normal viewing distance nobody sees it.
Primaries find subpixels that are off. Secondaries find subpixels that are on. On the cyan field the red subpixel is meant to be dark, so a red subpixel stuck on shows as a white dot. Magenta does the same for green, and yellow for blue.
Gray is for everything that is not a pixel. An even mid-gray field is the fastest way to see clouding, backlight bleed, uneven panel patches and the smears that a cloth left behind โ none of which are pixel faults, and all of which get reported as them.