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Dead Pixel Test
The Dead Pixel Test fills your whole screen with solid colours — red, green, blue, white, and black — so a dead or stuck pixel has nowhere to hide. Run it fullscreen on any monitor, laptop, tablet, or phone, and a faulty pixel shows up as a dot that stays put while the colour behind it changes.
Tip: clean the screen first — a speck of dust looks just like a dead pixel. Dim the room lights and look at the screen from a normal viewing distance, then move closer to check any suspect spot.
How it works
Every screen is made of millions of tiny dots called pixels, and each pixel is made of three sub-pixels — red, green, and blue — that mix to make every colour you see. A dead pixel is one whose transistor has stopped working, so it never lights up at all and stays black on every colour. A stuck pixel is one whose sub-pixel is frozen on, so it glows red, green, or blue no matter what the screen is supposed to show. On a normal photo or web page both faults are easy to miss, because the picture changes all the time and a single wrong dot blends in.
A solid-colour test removes the hiding places. When the whole screen is pure red, every pixel should be red — a dead pixel shows as a black dot, and a stuck green or blue pixel shows as a dot of the wrong colour. Pure green and pure blue each expose a different stuck sub-pixel. Pure white lights up all three sub-pixels at once, so any dead or dark pixel stands out sharply, and pure black turns everything off, so any pixel that is still glowing — a stuck pixel, or light leaking around the edge — is obvious. That is why the test runs through five colours instead of one: each colour catches a different fault.
Press Start Fullscreen Test and the screen fills with the colour you chose, edge to edge, with no menus or borders in the way. Click anywhere, tap the screen, or press any arrow key or the space bar to move to the next colour in the order red, green, blue, white, black, then back to red. Pick Auto-cycle instead and the colours change by themselves every few seconds, at the speed you set — useful when you want to watch the screen hands-free. The grid overlay draws faint lines across the screen so you can say exactly where a suspect spot is, for example "third row from the top, near the left edge", which helps when you report it to a seller or a repair shop.
To leave the test, press Escape, click the Exit button, or press the browser's fullscreen exit key. The test does not change any setting on your device and it does not fix anything — it only finds faults. Before you conclude a spot is a dead pixel, wipe the screen with a soft cloth and run the test again: dust, a crumb, and a smudge all look like dead pixels until you clean them off.
Worked example
A buyer has just unpacked a new laptop and wants to check the screen before the return window closes. She opens this page on the laptop, cleans the screen with a soft cloth, and presses Start Fullscreen Test with Red selected.
Step 1: The screen fills with solid red. She scans it slowly, left to right, top to bottom, and sees nothing out of place — every pixel is red.
Step 2: She clicks once and the screen turns green, then again for blue. On the blue screen she notices a tiny red dot near the top-right corner that does not belong.
Step 3: She clicks to white. The same spot shows as a small red dot on the white background, and on black it still glows red. The dot never moves and never changes colour.
Step 4: She turns on the grid overlay and notes the position — top row, about three-quarters across — then presses Escape to exit and takes a photo of the white screen showing the red dot.
The tool gives exactly this result: a fullscreen red screen, then green, blue, white, and black, with the same red dot visible on every colour. That is a stuck red pixel, not a dead one — a dead pixel would be black on all five screens. She has the photo and the position to send to the seller, and because she checked inside the return window, the laptop can be swapped.
FAQ
What is a dead pixel?
A dead pixel is a single dot on a screen that never lights up, so it stays black on every colour. It happens when the tiny transistor that drives that pixel stops working. A dead pixel is always black, which is what sets it apart from a stuck pixel, which stays lit in one colour.
What is a stuck pixel, and how is it different?
A stuck pixel is a pixel that is frozen on one colour — usually red, green, or blue — because one of its three sub-pixels is stuck on. On a white screen it shows up as a coloured dot, and on a black screen it glows. Unlike a dead pixel, a stuck pixel can sometimes be fixed by gently massaging the spot or by flashing colours over it for a few minutes.
How do I run the dead pixel test?
Press Start Fullscreen Test, then look at each solid colour in turn: red, green, blue, white, and black. Click, tap, or press any arrow key to move to the next colour. A spot that stays the same colour on every screen — or a dot that stands out on one colour — is a faulty pixel. Press Escape or the Exit button to leave the test.
Can this test fix a dead or stuck pixel?
No. The test only finds faulty pixels; it cannot repair them. A stuck pixel sometimes recovers on its own or after flashing colours rapidly over the spot, but a truly dead pixel is a hardware fault. If the screen is still under warranty, a photo of the faulty pixel on a solid-colour screen is usually what the manufacturer asks for.
Does this test work on phones and laptops too?
Yes. The test works on any device with a screen and a browser: a phone, a tablet, a laptop, or a desktop monitor. Open the page on the device you want to check, tap Start Fullscreen Test, and tap the screen to change colours. Check a new device within its return window so a faulty screen can still be swapped.