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Device test

Black — shows stuck pixels and backlight bleed

In fullscreen, tap or press a key for the next colour. Press and hold on a bad pixel to mark it (or right-click, or press M). Escape leaves.

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Dead pixel test: check a screen properly

Go fullscreen, step through six colours and mark anything that looks wrong. A dead pixel stays black on every colour; a stuck pixel shows the wrong one.

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The short answer

To check for dead pixels, go fullscreen and cycle through solid red, green, blue, white and black. A pixel that stays black on every colour is dead; one that stays lit on a single colour is stuck. Black reveals stuck pixels and backlight bleed best, white reveals dust and dead pixels.

How to use it

Five steps, about a minute

  1. Step 1: Clean the screen and turn the brightness up

    Wipe the screen with a dry microfibre cloth, set brightness to maximum and turn off night mode and auto-brightness, which tint or dim the test colours.

  2. Step 2: Go fullscreen

    Press Go fullscreen. Everything else leaves the screen, so every pixel is showing the test colour and nothing else.

  3. Step 3: Step through the six colours

    Tap, click or press any key for the next colour: black, white, red, green, blue and grey. Look across the whole screen on each one, corners included. The left arrow goes back.

  4. Step 4: Mark what you find

    Press and hold on a bad pixel to put a ring around it. With a mouse, right-click or hold Shift and click; with a keyboard, press M with the pointer over the spot. Marking the same place again clears it.

  5. Step 5: Leave and copy the result

    Press Escape. The result lists each mark by where it is on the screen. Copy it into a return request, or send it to the seller, along with a photograph of each spot.

Reading what you see

Dead, hot or stuck: what each one means

What the fault looks like, whether it can recover, and how it counts towards a return.

FaultWhat you seeDoes it recover?For a return
Dead pixelA black dot on every colour, clearest on whiteNoCounts as an always-dark fault. Class II panels may have 2 per million pixels
Hot pixelA white dot on every colour, clearest on blackRarelyCounts as an always-lit fault. Class II allows 2 per million, and some makers replace a panel for one
Stuck pixelA red, green or blue dot that vanishes on a field of its own colourSometimes, with rapid colour flashingA sub-pixel fault. Class II allows 5 per million pixels
Backlight bleedLight leaking in from an edge or corner on black, in a dark room. It stays put when you move your headNoNot a pixel fault, so there is no count. It is judged by eye: photograph it in a dark room
Dust or a markA soft-edged speck that seems to shift against the picture as you move your headWipe it offNot a fault. Clean the screen before you mark anything

The class figures come from ISO 13406-2, since carried into ISO 9241-307. Most consumer screens are sold as Class II, which works out at 4 always-lit, 4 always-dark and 10 sub-pixel faults at 1920 × 1080 (Full HD), 7 always-lit, 7 always-dark and 18 sub-pixel faults at 2560 × 1440 (QHD) and 16 always-lit, 16 always-dark and 41 sub-pixel faults at 3840 × 2160 (4K). A maker's own warranty can be stricter or looser, so read it for your model.

Getting it right

Four things worth knowing

  • Do it the day the screen arrives

    Manufacturer policies often allow a return for a small number of faulty pixels only within the return window. Finding one in month four is a very different conversation.

  • Clean the screen first

    Most of what looks like a stuck pixel is dust or a speck of dried spray. Wipe with a dry microfibre cloth before concluding anything.

  • Look from straight on, in a dark room

    Backlight bleed and clouding only show properly on a black field with the lights off. Off-angle viewing exaggerates both and will worry you unnecessarily.

  • A stuck pixel sometimes recovers

    Dead pixels do not come back, but stuck ones occasionally do. Rapid colour cycling over the area for a few minutes is the usual trick — worth trying before you start a return.

Nothing leaves your device

This test runs entirely in your browser. There is no upload, no recording and no server that could receive anything — close the tab and it is gone.

  • No sign-up and no account
  • Nothing recorded or stored
  • Works with an ad blocker on
  • Free, and staying free
FAQ

Questions people ask

Anything we've missed?

Tell us

What is the difference between a dead and a stuck pixel?

A dead pixel receives no power and stays black on every colour. A stuck pixel is permanently on in one colour, so it shows as a bright red, green or blue dot and disappears on a field of its own colour.

How many faulty pixels can I return a screen for?

It depends on the manufacturer and the panel grade — some allow a return for a single bright pixel, others require several. Check your specific warranty, and record what you find with a photograph.

Which colour should I check on?

All of them. Black shows stuck pixels and backlight bleed, white shows dead pixels and dust, and the solid primaries show sub-pixel failures that plain black and white can hide.

Can this fix a stuck pixel?

Sometimes. Rapid colour cycling over a stuck pixel can restart it, which is why the test includes a flashing mode. It shows a flashing-light warning first, stops by itself after five minutes, and never works on a dead pixel.

How do I record where a dead pixel is?

In fullscreen, press and hold on the pixel, or right-click it, and a numbered ring appears around it. When you leave fullscreen the result lists each mark by position, such as top left, 12% across and 8% down, ready to copy into a return request. Nothing is saved or sent anywhere.

Does this work on a phone or a TV?

Yes on a phone. For a TV, open the page in the TV's browser if it has one, or cast the tab — but be aware that video compression can hide a single pixel.

Is there a risk of burn-in from the solid colours?

For a few minutes, no. OLED burn-in comes from static images over many hours. Do not leave a solid field up all day.

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Photo by Helena Lopes on Unsplash
Before it matters

Find the problem now, not mid-sentence

Every one of these runs in the browser and checks one thing properly. Nothing is uploaded, nothing is recorded, and none of them need an account.

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