How to run a dead pixel and stuck pixel test properly
Give the screen a quick wipe with a dry microfibre cloth first — a speck of dust looks exactly like a dead pixel on a white background. Set brightness to where you normally use it, dim the room if you can, and sit at your usual viewing distance. Then press Start full-screen test. The page asks the browser for true full screen and hides the cursor, so nothing but the test colour is on the display. Run it on every new or second-hand screen: as a quick monitor test it also shows up banding, uneven backlighting and bleed at the edges, not just faulty pixels.
Move through the screens with the → key, Space, a click, a tap or a swipe; ← or a right-click goes back, and 1–9 jump straight to a colour. On each screen, scan slowly in strips from one corner to the other rather than staring at the middle — defects are easy to miss in your peripheral vision. Press Esc to leave at any time.
When you find something, point at it and press M (or long-press on a phone). The pixel's exact physical coordinates are saved in the Marked pixels list under the tool, and you can copy them into a report for a retailer. Your marks, custom colour and fixer settings are remembered on this device only; nothing is uploaded.
Which colour reveals which fault
Every pixel is made of three sub-pixels — red, green and blue. Each test screen switches a different combination of them on, which is why you need all of them rather than just white and black.
| Screen | What it reveals |
|---|---|
| White | Dead pixels (black dots) and dead sub-pixels, which show as a coloured dot — a missing blue sub-pixel leaves a yellow speck. |
| Black | Stuck and hot pixels glowing against the dark, plus backlight bleed and IPS glow at the edges. |
| Red, green, blue | Isolate each sub-pixel. A dark spot on red is a dead red sub-pixel; a green dot on red is a stuck green one. |
| Cyan, magenta, yellow | Two channels on, one off: a stuck sub-pixel of the missing colour stands out sharply. |
| Mid and dark grey | Uniformity problems — clouding, vignetting, tinted patches and the “dirty screen” effect. |
| Ramps and grey steps | Banding: all 256 levels should blend smoothly, and all 32 steps should be distinct. |
| Near-black / near-white squares | Crushed shadows or clipped highlights, usually a brightness, contrast or HDR setting. |
| 1-pixel checkerboard | Scaling blur, inversion flicker and shimmer, because every other physical pixel alternates. |
All patterns are drawn at your display's native pixel density, not the browser's CSS pixels, so the fine patterns are pixel-exact even with Windows display scaling at 125% or 150% or on a high-density phone.
Using the stuck pixel fixer
A stuck pixel is powered but its liquid crystal is not switching properly, so it sits on one colour. Rapidly cycling it through every state can sometimes work it loose. A dead pixel has a failed transistor and no software can bring it back — the fixer is only worth trying on dots that are lit or coloured.
- Mark the pixel during the test, then choose Fix here in the list — or start the fixer and drag the flashing square over it. On a touch screen you can simply tap where the pixel is.
- Pick the square size. Small keeps the rest of the screen usable; Whole screen is for when you cannot pin-point the pixel.
- Leave it running for 10 to 20 minutes. The timer only counts time the fixer is visible, so switching tabs doesn't cheat the run, and a wake lock stops the screen sleeping.
- When it chimes, check the pixel on the black and colour screens. Repeat two or three times before concluding it won't respond.
The fixer flashes fast. If you are photosensitive, don't use it; everyone else should start it and look away. The gentle speed flashes about ten times a second instead of at your refresh rate. A careful last resort for a stubborn stuck pixel on an LCD is light pressure through a soft cloth with the screen off, but it can make things worse and is not advisable on OLED panels or laptops with thin lids.
Is one dead pixel a valid return?
Often not, which surprises people. Most manufacturers follow a pixel policy based on ISO 9241-307 (formerly ISO 13406-2). Its common Class II tolerance allows, per million pixels, up to two always-lit pixels, two always-dark pixels and five sub-pixel faults — so a 1080p panel with roughly two million pixels can legally have a few. Many brands are stricter for bright pixels, and some promise zero bright dots on premium models, so read the policy for your exact model.
In the UK, a retailer must accept a faulty item within 30 days under the Consumer Rights Act, and a bright stuck pixel in the middle of a new screen is a reasonable argument that it isn't of satisfactory quality, whatever the manufacturer's class says. Test on the day it arrives, mark every defect, and copy the report — it lists physical coordinates, your screen's native resolution and the colour each fault was seen on. If colours look wrong across the whole screen rather than in single dots, check your resolution and scaling and run the refresh rate test for frame skipping; on phones and tablets, the touch screen test checks the digitiser too.
Browser limits worth knowing
- iPhone full screen. Safari on iPhone does not allow web pages to go true full screen, so the test fills the viewport and the address bar stays visible. Rotate to landscape and scroll the bar away, or temporarily move the page to the top of the screen, to check the pixels it covers. iPads and Android phones go fully full screen.
- Notches and rounded corners. Pixels hidden behind a camera cut-out cannot be displayed by any app.
- Colour filters. Night Light, Night Shift, True Tone, HDR tone-mapping and ICC profiles all tint the output. Turn them off before judging banding or uniformity.
- Esc in full screen. Browsers reserve Esc for leaving full screen, so a single press both exits full screen and closes the test.
Frequently asked questions
What is the difference between a dead, stuck and hot pixel?
A dead pixel never lights, so it shows as a black dot on every colour. A stuck pixel is stuck on one colour — red, green, blue or a mix — and is easiest to see on black. A hot pixel is a stuck pixel with all three sub-pixels on, so it glows white. Stuck and hot pixels can sometimes be fixed; dead ones cannot.
Can a stuck pixel fixer really fix a stuck pixel?
Sometimes. Flashing a stuck pixel rapidly through every colour can free a liquid crystal that isn't switching properly, and it costs nothing to try for 10 to 20 minutes, two or three times. It won't work on a dead pixel, whose transistor has failed, and it can't be guaranteed on a stuck one. If nothing changes after several runs, the fault is permanent.
Is it just dust, or a dead pixel?
Dust sits on the surface and usually looks slightly soft and larger than one pixel; a dead pixel is a perfectly sharp, square dot aligned with the grid. Wipe the screen with a dry microfibre cloth and look again from an angle. A mark that moves or disappears was dirt. A mark that stays exactly in place on every colour is in the panel.
Does this dead pixel test work on phones and tablets?
Yes. Tap to go to the next colour, swipe to move back and forth, and long-press on a bad pixel to mark it. Android phones and iPads switch to true full screen. On iPhone, Safari keeps the address bar visible, so rotate to landscape and scroll it away to check the pixels underneath. The fixer square can be dragged with a finger.
How long should I run the stuck pixel fixer?
Start with 20 minutes, then check the pixel on the black and colour screens. If it has faded or changed colour, it is responding — run it again. If nothing has changed after three runs of 20 to 30 minutes, the fixer is unlikely to help. Some people leave it for several hours; this does not harm an LCD or OLED panel, because the image never stays still.
Why do I see stripes in the gradient screens?
That is banding. Some is normal on 6-bit panels that use dithering, or on cheap TN screens. Heavy banding usually comes from software: a night-light filter, a colour profile, limited-range RGB output from the graphics card, or brightness and contrast set to extremes. Turn those off and test again before blaming the monitor.