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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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Monitor dead pixel test: check a new display properly

Do this the day it arrives. Manufacturers accept a pixel fault only within a set window and above a set number, and both are easier to meet now.

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The short answer

To test a monitor for dead pixels, go fullscreen and cycle through red, green, blue, white and black at full brightness from about 50cm away. A pixel black on every colour is dead; one lit on a single colour is stuck. Photograph anything you find straight away — manufacturers usually want evidence inside the return window.

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

  • Photograph the fault with something for scale

    A photo of a bright dot on a black field, with a ruler or a coin beside it, is far harder to dismiss than a description. Take it the day you find it.

  • Know the class your panel is sold under

    ISO 9241-307 defines pixel fault classes, and most consumer monitors are Class II, which permits a small number of faults before the panel counts as defective. Retailers are often more generous than manufacturers, so ask both.

  • Test at native resolution

    Scaling blends a faulty pixel with its neighbours and can hide it completely. Set the display to its native resolution before you look for anything.

  • Check the corners on black with the lights off

    Backlight bleed and IPS glow show at the edges on a dark field in a dark room. Some is normal on IPS; a bright patch that is obvious during a film is not.

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.

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FAQ

Questions people ask

Anything we've missed?

Tell us

How many dead pixels before I can return a monitor?

It varies by manufacturer and panel class. Some accept a single bright pixel, others require several. Check the warranty text for your model, and check the retailer's return policy separately — it is often the easier route.

What is the difference between backlight bleed and IPS glow?

Bleed is light escaping at the edges and stays put as you move. Glow is a wash across a corner that shifts with your viewing angle. Bleed can be a warranty fault; glow is a property of the panel type.

Will a dead pixel spread?

No. A dead pixel is a single failed transistor and does not affect its neighbours. New faults appearing over time is a different problem and worth reporting.

Should I test a second-hand monitor before buying?

Yes, and take a phone with this page already open. Five minutes of colour fields is the cheapest inspection available.

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