Dead Pixel Test
Step through eleven full-screen colour fields to find dead, stuck and hot pixels — then try to un-stick them. Everything runs locally in your browser.
Clean the screen, turn the lights down, then run the check. Tapping or clicking anywhere advances to the next field, except the left third of the screen, which goes back; arrow keys and Space work too, and Esc exits at any time.
Screen size is an estimate: it is the size the browser reports multiplied by the device pixel ratio, which is only your true panel resolution if browser zoom is at 100%.
This tool only paints colours onto your screen. It never reads the screen, never touches your camera or microphone, and nothing is uploaded anywhere.
Stuck-pixel exerciser
In small window mode a movable box appears — drag its bar to park it over the bad pixel, or focus the bar and nudge it with the arrow keys (hold Ctrl to resize, Shift for bigger steps). Drag the bottom-right corner to resize with the mouse. Stop with this button or Esc. Only stuck subpixels ever respond to this; dead pixels will not change.
The countdown only advances while this tab is visible and drawing, so time spent in a background tab is not counted as exercising. Where the browser supports it, a screen wake lock is held during the run and released the moment you stop.
How to run the check
- Clean the screen first. A speck of dust or a dried droplet is by far the most common “dead pixel”. Use a dry microfibre cloth; if it needs moisture, dampen the cloth, never the panel.
- Kill the room lights and get close — closer than you normally sit. One dead subpixel on a 24-inch 1080p monitor is about 0.09 mm across. From a metre away you simply will not see it.
- Step through all eleven fields and give each one a couple of seconds. Click or tap anywhere to advance, the left third of the screen to go back, or use ← / →, Space, Home and End. Turn on auto-advance if you would rather keep your eyes on the panel than on the mouse.
- Black field: hunt for light. Any point that glows is a hot (always-on) pixel or a stuck subpixel. This is the single most revealing field — a lit dot on black is far more visible than a dark dot on white.
- White field: hunt for darkness. Any dark point is a dead or stuck-off pixel. If the dot smears when you wipe it, it was dirt.
- Red, green and blue: find the subpixel. A dot that is dark only on the red field is a dead red subpixel — on white that same fault shows up as a faint cyan speck that is easy to miss entirely.
- Write down where it is, and photograph it. A phone photo of the black field with a lit pixel on it is the evidence retailers actually accept. Then decide: same colour on every field means stuck and the exerciser is worth a try; black on every field including white means dead, and no software will change that.
Dead, stuck, hot — what you are actually looking at
Every pixel on an LCD is three subpixels sitting side by side: one red, one green, one blue, each with its own transistor in the panel’s active matrix. The panel drives them independently, and almost every “dead pixel” anyone finds is really one subpixel misbehaving. That is the whole reason this test cycles through primaries instead of just showing you a white screen.
Dead (dark) pixel — Type 2 fault
The subpixel receives no drive at all. It reads black on every field, including white. On an LCD this is usually a failed thin-film transistor; on an OLED it is a burnt-out or shorted emitter. Either way the fault lives in the glass, not in the signal, so nothing running on your computer can touch it. A dead pixel is a returns question, not a software question.
Hot / bright pixel — Type 1 fault
The opposite failure: the pixel is driven full-on and never switches off, so it is a hard white dot on the black field and invisible on the light ones. Bright faults are the ones people actually notice, which is why several manufacturers allow fewer of them than dark ones.
Stuck pixel — Type 3 fault
Here the drive is working and the liquid-crystal cell for one subpixel is simply jammed in the wrong state. A red-stuck subpixel shows a red dot on the black field, looks perfectly normal on the red field, and tints white areas pink at that one spot. This is the only category the exerciser can help with, precisely because the electronics are intact — the cell just is not relaxing.
Things that are not pixel faults at all
- A dark speck that moves or smears when you wipe — dust or grease on the polariser.
- A soft glow at the corners of the black field that changes with viewing angle — backlight bleed or IPS glow, a uniformity issue, not a pixel.
- A diffuse pale blotch — a pressure mark, usually from something pressing on the panel in transit.
- An entire row or column that is dark or the wrong colour — that is a driver-IC fault. It is unfixable and it is an RMA, but it is not a dead pixel.
- A faint stationary ghost of previous content on an OLED — that is retention or burn-in. Different problem, different tool: see the OLED burn-in test.
What the exerciser does — and what it cannot do
It repaints the area under it with fully saturated random red/green/blue noise about 20 times a second, drawn at your display’s real device-pixel grid so that each physical subpixel gets its own value rather than a blurred average. Ten minutes is roughly twelve thousand repaints — but each subpixel is re-rolled on or off independently every time, so it only actually changes state on about half of them: call it six thousand on/off transitions per subpixel, not twelve thousand. The theory is that this can shake a jammed liquid-crystal cell back into responding.
Be clear about the evidence: this is a folk remedy with a large pile of anecdote and no controlled study behind it. It sometimes works on stuck subpixels. It cannot restore drive to a dead transistor, it cannot un-burn an OLED emitter, and on an OLED a long run is actively a bad trade — you are hammering one small area at maximum output on a panel that ages with use. If ten minutes and then twenty more change nothing, stop.
The other folk remedy is gentle pressure: with the screen off, press the fault with a soft cloth over a fingertip, hold a few seconds, release, then power on. It occasionally frees a stuck LCD cell. It also permanently damages panels when people press hard, and it does nothing at all on OLED. Your call, but the exerciser cannot break anything and the pressure trick can.
Warranty: the numbers that decide your claim
Panels are graded against the pixel fault classes defined in ISO 13406-2 and carried forward into ISO 9241-307. The standard has been revised since, but manufacturers still quote these class numbers. Allowances are per million pixels:
| Class | Type 1 · bright | Type 2 · dark | Type 3 · stuck subpixel |
|---|---|---|---|
| I | 0 | 0 | 0 |
| II | 2 | 2 | 5 |
| III | 5 | 15 | 50 |
| IV | 50 | 150 | 500 |
Most consumer monitors, laptops and TVs ship as Class II. A 1920×1080 panel is 2.07 megapixels, so a Class II panel is allowed roughly four bright pixels, four dark pixels and ten stuck subpixels before it is out of spec — and a 4K panel, at 8.3 megapixels, is allowed four times that. Which is the blunt answer to “can I return it for one dead pixel?”: on the panel warranty alone, almost never. Two routes work better. The retailer’s return window (14 days by law across the EU and UK for distance sales, 15–30 days as policy at most large US retailers) does not care how many pixels are dead. And a zero-bright-pixel or perfect-panel guarantee, sold as an option by some manufacturers and bundled by some monitor specialists, is the only thing that reliably makes a single fault actionable.
Before you trust what you saw
- Colour management can soften the primaries. On a wide-gamut display the browser may convert sRGB #ff0000 into the panel’s own primaries, so the red field does not necessarily drive the red subpixel to its absolute maximum. It is still far more than enough to expose a dead or stuck subpixel — but for a marginal fault, cross-check with the monitor’s own built-in test pattern.
- HDR desktop mode lies about black. With HDR enabled in Windows, SDR content is tone-mapped: blacks can be lifted or crushed and a dim stuck subpixel can vanish. Turn HDR off before judging the black field.
- Content-adaptive backlight. Laptops with CABC or Intel’s Display Power Saving dim the backlight on a bright full-screen field and lift it on a dark one. If the white field visibly fades a second after it appears, that is the driver reacting to the image, not a panel fault. Disable it in the GPU control panel or BIOS before testing.
- Local dimming blooms. On a mini-LED or full-array panel a single lit pixel on black will sit inside a halo. The halo is the backlight zone, not the pixel.
- Never test over a stream. Remote desktop, screen mirroring and casting all re-encode the image, and single-pixel detail is the first thing a video codec discards. Run this on the machine physically attached to the panel.
- Without the Fullscreen API you are not testing the whole screen. If your browser refuses full screen (this is normal in iOS Safari and inside embedded browsers) the check covers the page only, and whatever is behind the browser’s own bars never gets tested.
- Density beats eyesight. On a phone at 3× density a single dead subpixel is under 25 micrometres wide. If you cannot find it from 10 cm, you are not going to notice it in use either.
FAQ
What is the difference between a dead pixel and a stuck pixel?
A dead pixel gets no drive at all, so it stays black on every field — including white. A stuck pixel is jammed on: a red-stuck subpixel shows a red dot on the black field and tints white areas pink. The distinction matters because the exerciser on this page can sometimes free a stuck cell, and can never do anything for a dead one.
Can software really fix a dead pixel?
No. Nothing running on your computer can restore drive to a pixel that is not receiving any — the fault is a broken transistor or a burnt-out emitter inside the panel. Flashing patterns only ever help a stuck subpixel, where the drive works and the liquid-crystal cell is sitting in the wrong state. Treat any tool that promises to fix dead pixels as marketing.
How long should I run the stuck-pixel exerciser?
Start with 10 minutes and look again. Most reported successes happen in the first 10 to 30 minutes, and there is little point going past about an hour in total. On an OLED keep runs short — you are driving a small area at full brightness, which is exactly how you age a panel unevenly.
How many dead pixels does a warranty actually cover?
Panels are graded against the ISO pixel fault classes. Class II, which covers most consumer screens, allows 2 bright and 2 dark pixels plus 5 stuck subpixels per million pixels — so a 1080p monitor can carry roughly four dead pixels and still be in spec. One fault rarely wins a claim on its own. The retailer’s return window, or a manufacturer’s zero-bright-pixel guarantee, is usually the better route.
Why does my faulty pixel look coloured instead of black?
Because a pixel is three subpixels — red, green and blue — and usually only one of them has failed. A pixel with a dead red subpixel is not black, it is cyan; one with a stuck green subpixel glows green on a black screen. That is why the check steps through pure red, green and blue fields as well as white and black.
Does this work on a phone, a tablet or a TV?
Yes, anywhere with a browser. Turn brightness up and switch off auto-brightness and any night or blue-light filter first. On iPhone, Safari will not let a web page take over the whole screen, so the browser’s own bars stay visible and cover part of the panel. On a TV, use a neutral or PC picture mode — the movie and vivid presets crush blacks and can hide a dark subpixel completely.