Dead Pixel Test

The Dead Pixel Test fills your screen with solid colours so that a single misbehaving pixel has nowhere to hide. Where most pixel testers stop at showing you the colours, this one asks you to click every bad spot you find and then tells you what each one actually is — a dead pixel, a hot pixel, or one specific stuck subpixel — along with whether it is worth trying to fix. It works on any screen with a browser: monitors, laptops, phones, tablets and TVs.

What a dead pixel actually is

Your screen is a grid of pixels, and every pixel is built from three subpixels: one red, one green and one blue, sitting side by side as tiny stripes. Mixing their brightness produces every colour you see. Yellow is red and green at full brightness with blue off; white is all three at full; black is all three off.

A dead pixel is one whose three subpixels have all stopped lighting, usually because the transistor driving them has failed. It stays black permanently, which is why it leaps out against a white background and becomes completely invisible against a black one. A stuck pixel is a different fault entirely: it still receives power but is latched at a fixed value, so it stays lit. And because the three subpixels fail independently, the most common defect of all is a single stuck or dead subpixel — a dot that is not black or white but red, green, blue, cyan, magenta or yellow.

Dead, stuck and hot — the differences that matter

These names get used interchangeably online, but they describe genuinely different faults with different odds of being repaired:

How to use the Dead Pixel Test

1. Clean your screen first with a dry microfibre cloth, and dim the room if you can. Dust and reflections are mistaken for dead pixels far more often than real dead pixels are found.
2. Choose a test set. Quick Check runs black, white and the three primaries in about 30 seconds and finds every defect. Full Sweep adds the secondary colours, greys and a gradient, and it is the only set that can name the exact broken subpixel.
3. Press Start Full-Screen Test. The page takes over your whole screen with the first colour. Use the arrow keys, or the arrows in the control bar, to move between screens.
4. Click or tap every bad spot you see. A ring marks it. Clicked something by mistake? Click the ring again to remove it.
5. Check the same spots on every screen. Once you have marked a spot, a faint dashed ghost ring stays at that position on all the other screens. Wherever you can still see the defect, click the ghost ring to confirm it. This is the step that makes the diagnosis possible.
6. Press Analyze. Every marked spot comes back identified, positioned, and — if it is a stuck one — with a button that drops the fixer straight onto it.

How this test identifies the exact fault

This is what separates a real diagnosis from a colour slideshow. Each of the three subpixels is in one of three states — healthy, jammed on, or dead — which gives 26 possible faults for a single pixel. Every one of those 26 has a unique fingerprint: the exact set of test colours it is visible against.

Take a red subpixel jammed on. Against a red screen it is invisible, because the background already asked that subpixel for full red and it is delivering exactly that. Against black it glows red. Against green it turns yellow, and against blue it turns magenta. Now take a dead red subpixel, which does the precise opposite: it goes black against the red screen and tints the white screen cyan, while the green and blue screens can say nothing about it at all.

So when you mark a spot on some screens and not others, you are not just pointing at a dot — you are handing over a fingerprint. This tool simulates all 26 faults against the screens you actually displayed and keeps only the ones whose predicted fingerprint matches what you marked. On a Full Sweep, exactly one always survives, which is why the report can tell you not merely "stuck pixel" but "stuck green subpixel".

What each test screen reveals

The black and white screens do the heavy lifting for pixel faults: between them they separate "too dark" from "too bright", which is the single most useful split there is. The primaries isolate one subpixel each. The secondaries — cyan, magenta and yellow — are the cross-check that resolves faults involving two subpixels at once. The greys and the gradient are not looking for pixels at all; they reveal panel-wide problems such as clouding, backlight bleed, IPS glow and colour banding, which is why this tool reports anything seen only on those as a uniformity issue rather than a broken pixel.

How to fix a stuck pixel

A stuck subpixel is still powered — it has simply settled into one position and stopped responding. Flashing rapid random colours over it forces the liquid crystal cell to switch state many times a second, and that repeated exercise is often enough to shake it loose. That is exactly what the built-in fixer does: drag the flashing box over the defect and leave it running.

• Give it time. Ten minutes frees many recently stuck pixels. Some need 30 minutes or several sessions. Some never come back.
• Recent beats old. A pixel that stuck yesterday has far better odds than one that has been stuck for a year.
• It cannot hurt a healthy pixel, so there is no risk in trying — beyond the flashing itself, which is why the tool asks first.
• Skip the pressure trick. Rubbing or pressing a stuck pixel with a cloth is widely repeated advice, and it can permanently damage the panel or create new defects. Software flashing carries none of that risk.
• Dead pixels do not respond to any of this. There is nothing to exercise — the pixel is not receiving power at all.

Dead pixel warranty policies and ISO 9241-307

Finding one dead pixel rarely qualifies a screen for replacement, which surprises most people. Manufacturers sell panels against the pixel fault classes in ISO 9241-307, and almost all consumer screens are sold to Class II:

Those allowances are counted per million pixels, so a 4K screen with roughly 8.3 million pixels is permitted several times the headline figure before it counts as faulty. That is why a single dead pixel usually does not qualify. The good news is that many premium monitor makers and retailers advertise their own stricter zero bright pixel or perfect panel guarantee that overrides the standard, and return windows apply regardless of pixel policy. Check your specific warranty document rather than the standard, and if you plan to claim, keep the defect count and positions from your report — the position of each defect is recorded as a percentage across and down the screen, which stays meaningful whatever resolution you tested at.

Tips for an accurate test

• Clean the screen before you start. Most "dead pixels" reported online are dust. If a spot shows on both the black and the white screen, this tool flags it as a blemish, because no pixel fault can do that.
• Test at native resolution. A scaled or non-native resolution blurs pixels together and can hide a single-subpixel fault entirely.
• Look straight on. A spot that only appears from an angle is far more likely to be a coating flaw or a smudge than a pixel fault.
• Dim the room. Reflections easily hide a small dark defect on the white screen.
• Do not rush the black screen. Give your eyes a few seconds to adjust; faint stuck pixels emerge only once they do.
• Be systematic. Scan in a grid — corners and edges last, since that is where defects are easiest to miss.
• Test a new screen immediately. Return windows are short, and they are usually far more generous than pixel warranty policies.

Frequently Asked Questions

What is a dead pixel?
A dead pixel is a single point on your screen that no longer lights up at all. Each pixel is made of three subpixels — red, green and blue — and in a dead pixel all three are permanently off, so the spot stays black no matter what is displayed. It shows as a tiny black dot on a white or brightly coloured background and disappears on a black screen. Dead pixels are a hardware fault caused by a failed transistor and cannot be repaired by software.

What is the difference between a dead pixel and a stuck pixel?
A dead pixel receives no power and stays black. A stuck pixel still receives power but is latched at a fixed value, so it stays lit. That difference is what makes this test worth running: a stuck pixel appears as a bright white, red, green or blue dot against a black screen and vanishes on white, while a dead pixel does the exact opposite. Stuck pixels can often be revived with rapid colour flashing. Dead pixels cannot.

Can dead pixels be fixed?
Genuinely dead pixels cannot be fixed by software. The transistor driving the pixel has failed, so no pattern of colours can reach it. Stuck pixels are a different matter and often do respond to the flashing fixer built into this tool, because the subpixel is still powered and just needs to be cycled. That is exactly why identifying which type you have is worth the extra minute.

How does this test know which subpixel is broken?
Every fault has a unique fingerprint across the test screens. A red subpixel jammed on is invisible against a red screen, because it already matches the background, but glows against black and turns a green screen yellow. A dead red subpixel does the reverse: it goes black on the red screen and tints white cyan. There are only 26 possible combinations of three subpixels being healthy, jammed on or dead, and this tool simulates all 26 against the screens you actually viewed, keeping the ones that match what you marked. On a full sweep of all 12 screens, exactly one always survives.

How many dead pixels do I need for a warranty replacement?
It depends entirely on the manufacturer. Most consumer screens are sold to ISO 9241-307 pixel fault class II, which permits up to 2 permanently lit pixels, 2 permanently dark pixels and 5 defective subpixels per million pixels. On a 4K screen with roughly 8.3 million pixels, that allowance is quite generous. Premium monitors and many laptop makers advertise a stricter zero bright pixel policy. Check your specific warranty document, and record the defect count and positions from your report if you plan to claim.

Does the stuck pixel fixer actually work?
Sometimes. Flashing rapid random colours over a stuck subpixel forces it to switch state many times per second, which can free a liquid crystal cell that has settled in one position. It is not guaranteed and works better on recently stuck pixels than on long-standing ones. Run it over the defect for 10 to 30 minutes, then retest. It cannot damage a working pixel, but it does flash quickly, so skip it if you are sensitive to flashing light.

Should I test in a dark or a bright room?
A dim room is best. Reflections on a bright screen hide small defects and can make dust look like a stuck pixel. Clean the screen with a dry microfibre cloth first, sit at your normal viewing distance, and view the screen straight on rather than at an angle. If a spot only appears from one angle it is far more likely to be a smudge than a pixel fault — which is why this tool flags anything visible on both the black and white screens as a blemish rather than a defect.

Does this work on a phone or a TV?
Yes. The test fills whatever viewport it is given, so it works on phones, tablets, laptops, monitors and any TV with a browser. On a TV, open the page in the built-in browser or cast the tab. OLED screens are worth a mention: they very rarely have stuck pixels, but the black screen is an excellent way to check for the faint permanent image retention that OLED panels are prone to instead.

Is anything uploaded or stored?
No. The whole test runs in your browser. The only thing that ever leaves the page is the summary of your own marks encoded into the result link — which is what lets you bookmark or share a report — and even that contains nothing but positions and colour names.