Dead pixel test

Nine full-screen colours and an exerciser. Tells a dead pixel from a stuck one — different faults, different outcomes.

Black · 1 of 9

The key background: any lit dot leaps out. It also shows light bleed at the edges.

The colour already fills the panel below, so you can work through them without leaving the page. Checking the true edges needs full screen, because the browser chrome covers the top strip.

Dead pixel

Always black, on any background. It receives no current and cannot be fixed.

Stuck pixel

Always lit red, green or blue. One subpixel is frozen on; sometimes it recovers.

Always-white pixel

All three subpixels lit at once. Most visible against black.

Patch or area

Not a pixel: usually pressure on the panel or uneven backlight.

Stuck pixel exerciser

Rapid colour flashing in a small area. It sometimes frees a stuck pixel by forcing the liquid crystal to move. It does nothing for a dead one, which receives no current at all.

Contains rapid flashing. Do not use it if you have photosensitive epilepsy.

Generated right here, in your browser. What you type never leaves your device.

Keep going with Screen test Monitor calibration Screen burn-in test Refresh rate test

A faulty pixel is practically invisible over a photo or a web page, because the content keeps changing and the eye forgives it. Over a solid colour filling the whole screen it leaps out immediately. That is the entire trick behind this test.

The sequence starts on black deliberately: a lit pixel against black is the easiest defect there is to spot. It then runs the primaries, which isolate one subpixel each, and the secondaries, which isolate by absence — a red dot on cyan can only be a red subpixel stuck on.

And it helps to know before starting that dead and stuck are not the same thing. One cannot be fixed and the other sometimes can, and the difference shows in a second with the right colour.

Manual

How to use it

1
Clean the screen first

A speck of dust looks a great deal like a dead pixel against white. Wipe it with a dry microfibre cloth before you start and save yourself the fright.
2
Go full screen

Outside it the browser chrome covers the top strip of the display, which is exactly where manufacturing defects and knocks tend to concentrate.
3
Start on black

It is the background where any lit dot is obvious. Use it to check the edges too: a pale halo in the corners is backlight bleed, very common on IPS panels.
4
Work slowly through all nine colours

With the arrow keys or automatic mode. Look closely, moving your eyes zone by zone rather than trying to take in the whole screen at once. A pixel is tiny and gets lost in peripheral vision.
5
Note which colour reveals the dot

That is what tells you which subpixel is at fault. A dot that is black on red but vanishes on green and blue means the red subpixel is dead. A dot that is red on cyan means it is stuck on.

In depth

Things worth keeping in mind

Dead, stuck and always-on

A dead pixel receives no current: its transistor has failed and it stays black whatever the screen shows. No software or trick recovers it, because there is nothing left to move.

A stuck pixel does receive current, but one of its subpixels has frozen at a value. It shows as a permanent red, green or blue dot. Since the liquid crystal is still alive, it can sometimes be freed by forcing it to change many times over, which is what the exerciser does.

Dead: black on any background · no fix
Stuck: always the same colour · sometimes recoverable
Always-on: white against black, all three subpixels frozen
Smears and halos: not pixels — pressure or backlight

Why each colour reveals something different

Every pixel is made of three subpixels: red, green and blue, side by side. A pure red background lights only the reds and switches off the other two, so a dead red subpixel shows as a dark dot there and on no other colour.

The secondaries work the other way round and are the most useful for stuck pixels. Cyan is green plus blue with no red at all: a reddish dot on a cyan field means that subpixel is on when it should be off. The same goes for magenta and green, and yellow and blue.

What is not a pixel

Much of what people take for faulty pixels is not. A diffuse patch that changes shape when you look from another angle is usually pressure on the panel — from a finger pressing, a backpack, the laptop lid itself.

A glow in the corners against black is backlight bleed, and on IPS panels it is so common that manufacturers do not treat it as a defect. An uneven cloudy look over grey is non-uniformity, typical of VA panels. None of the three can be fixed, but none of them worsens either.

A patch that shifts with viewing angle: pressure on the panel
A halo in the corners against black: backlight bleed
Irregular clouds over grey: panel non-uniformity
A dot that moves when you wipe: it was dust

What the warranties actually say

Almost no manufacturer replaces a screen over one pixel. They work to ISO 9241-307, which defines tolerance classes for how many defects of each type each panel category allows. Most consumer monitors are class II, which tolerates several faulty pixels before entitling you to anything.

The thresholds usually distinguish between always-on pixels, always-off pixels and individual subpixels, and are stricter about the first because they are more visible. Before claiming it is worth counting exactly how many there are and of what kind — which is precisely what this test lets you do.

History

From the tube to the flat panel

CRT monitors had no dead pixels, and that is one reason the transition was resisted. A tube draws the image with an electron beam sweeping the screen; there is no grid of independent elements that can fail one at a time.

Liquid crystal was discovered in 1888, when the botanist Friedrich Reinitzer noticed that cholesteryl benzoate had two melting points and behaved strangely between them. More than eighty years passed before it displayed anything.

The first working LCD came in 1968, from George Heilmeier at RCA. It was monochrome and painfully slow, but it consumed a fraction of any alternative, and that carried it into the calculators and digital watches of the seventies.

The transistor-per-subpixel — the T in TFT — is what made large, fast panels possible, and with it came the failure mode this page is about. Every subpixel now depends on its own transistor, and one broken transistor among several million is statistically inevitable: hence tolerance standards rather than a promise of zero defects.

1888: Liquid crystal discovered
1968: First LCD display
3: Subpixels per pixel
ISO 9241-307: Tolerance standard

How it works

What sits behind each dot

An LCD emits no light of its own. Behind it a sheet illuminates constantly, and in front a layer of liquid crystal acts as a shutter: depending on the voltage applied, it lets through more or less light. Colour comes from a fixed filter on top, in red, green and blue stripes.

Each subpixel has its own tiny transistor, which is where TFT gets its T. That transistor applies the voltage that opens or closes the shutter. If it breaks, the shutter stays shut forever: the subpixel never lights again, and that is a dead pixel.

A stuck pixel is a different failure. The transistor works, but the liquid crystal in that cell has settled into a fixed orientation, sometimes from contamination, sometimes from showing the same thing for a very long time. Because current is still available, forcing rapid changes can reorient it, which is why the exerciser only makes sense in this case.

On an OLED panel the situation changes entirely: there is no backlight and no shutter, each subpixel emits its own light. There a dead pixel is a diode that has stopped emitting, and there is nothing to unstick. In exchange an OLED shows perfect black, which makes any lit dot even more obvious.

The exerciser on this page changes colour about sixteen times a second in a small area. The idea is to subject the cell to rapid, repeated transitions for a sustained period, in the hope the crystal regains mobility. It works sometimes, mostly on recent sticking, and not always.

By hand

The pressure method, and why to use it carefully

This is the other classic remedy for a stuck pixel. It can work and it can make things worse, so it is worth knowing exactly what you are doing before touching anything.

1

Put it on a background that highlights it and mark its position with a sticky note on the bezel. Once the screen is off you will not know where it was.
2

Pressing with the panel powered does not help and raises the risk of leaving a permanent mark.
3

A pencil eraser wrapped in microfibre. Never a fingernail or anything hard. Gentle, steady pressure for about ten seconds, on that spot only.
4

The idea is for the liquid crystal to reorder as current arrives while it is displaced.
5

Pressing harder does not raise the odds, but it does raise the risk of permanently damaging the panel and creating a mark far more visible than the original pixel.

Diagnosis

If something is not working

Symptom:I see a black dot against white

Likely cause:: It may be a dead pixel or it may be dust. The distinction is trivial and plenty of people skip it.
What to do:: Wipe with a dry microfibre cloth. If the dot moves or disappears, it was dirt. If it stays in exactly the same place across every colour, it is a dead pixel and cannot be fixed.

Symptom:There is a fixed coloured dot, always the same

Likely cause:: A stuck pixel: one subpixel has frozen on. The transistor works; it is the liquid crystal that will not move.
What to do:: Run the exerciser for its full sixty seconds and repeat it two or three times. If it will not give, the pressure method is the other option, with the precautions described. Recent sticking recovers far more often than sticking that is years old.

Symptom:There is brightness in the corners against black

Likely cause:: Backlight bleed. Light from behind escapes at the edges where the panel does not seal completely.
What to do:: It cannot be fixed and on IPS panels it is so routine that it is not treated as a defect. Only worth claiming if it is very pronounced and the monitor is new. Lowering brightness masks it considerably.

Symptom:Irregular clouds appear over grey

Likely cause:: Panel non-uniformity, typical of VA technology and some IPS panels.
What to do:: It is a characteristic of the panel rather than a fault, and it does not progress. It shows mostly in dark, uniform scenes. No setting removes it.

Symptom:Several dots appeared at once after a move

Likely cause:: Pressure or impact on the panel. It usually shows as a group rather than isolated dots.
What to do:: If the shape is a patch or a line, it is physical damage and there is no viable repair: replacing the panel typically costs close to the value of the monitor. Count and photograph the defects before claiming on insurance or from the courier.

Symptom:I can see a faint image of what was there before

Likely cause:: Image retention. On LCD it is usually temporary; on OLED it can become permanent.
What to do:: Leave the exerciser or a colour video running for half an hour: on LCD it almost always clears. On OLED, avoid leaving fixed elements on screen for long and use the panel maintenance cycle if your television has one.

Trivia

Things worth knowing

A 4K panel has nearly 25 million transistors just for the image

3840 × 2160 pixels, three subpixels each, gives 24.9 million subpixels with a transistor apiece. A few failing is statistics, not poor manufacturing.

Liquid crystal was discovered by a botanist

Friedrich Reinitzer was studying cholesterol in plants in 1888 when he found a substance with two melting points. It took eighty years to become a display.

Subpixels are not always in vertical stripes

Many OLEDs use arrangements like PenTile, which shares subpixels between neighbouring pixels. The same defect can therefore look different depending on the panel technology.

Manufacturers do not promise zero defects

ISO 9241-307 defines tolerance classes, and most consumer monitors are class II, which allows several faulty pixels without entitling you to a replacement.

Black on an OLED is genuinely off

There is no backlight to block: the pixel simply does not emit. That is why on an OLED the black background in this test is the most revealing of them all.

Questions

Frequently asked questions

Can a dead pixel be fixed?

No. A dead pixel has a failed transistor and receives no current, so there is nothing to move. What does sometimes recover is a stuck pixel, which is a different fault: it receives current but the liquid crystal has frozen.

Does the exerciser actually work?

Sometimes, and only on stuck pixels. Forcing rapid transitions can return mobility to the liquid crystal. It is more likely to work if the sticking is recent. On a dead pixel it does nothing whatsoever.

How many faulty pixels entitle me to a replacement?

It depends on the panel class under ISO 9241-307. Most consumer monitors are class II and tolerate several before entitling you to anything. Count how many there are and of what type before claiming, because the thresholds distinguish between always-on, always-off and individual subpixels.

Does it work on a phone or a television?

Yes, on any screen with a browser. On televisions use the built-in browser or connect a computer, and bear in mind many apply image processing that can slightly soften what you see.

A dot is only visible from certain angles — what is it?

Almost certainly not a pixel. Pixel defects look the same from any angle. Something that changes with position is usually pressure on the panel, a delaminated layer, or a reflection.

Is the exerciser flashing dangerous?

It changes colour about sixteen times a second, within the range that can trigger seizures in people with photosensitive epilepsy. If that applies to you, do not use it. The solid colours of the main test do not flash and are safe.

Do dead pixels get worse over time?

A dead pixel does not spread: the transistor behind it has failed, and that failure stays where it is. What does happen is that a panel which produced one defect can produce another later, for the same reason it produced the first — millions of transistors and ordinary odds. So a second dot months later is not the first one growing, it is a separate event. A whole dark line rather than a dot is different and worse: that is the row or column driver, not a pixel.

Is one dead pixel bad?

For the panel, no — it does not lead to anything else. For you it depends entirely on where it sits: a dot near an edge disappears from your attention within a day, one in the middle of the screen is the kind of thing you keep catching for years. The practical move is to count and locate them now, while you are inside the return window, because that is the only stretch of time when the decision is still yours.