Screens · guide

Black marks on computer screen, and how to tell them apart

By Alberto Gulotta · Updated 11 September 2026 · 16 min read

Black marks on computer screen come from four different things, and telling them apart costs nothing. Dust sits on the glass. A dark pixel is one point that has stopped working. A patch is damaged crystal underneath. A crack spreads. Four tests, in order of price, separate them before anybody is paid.

The reason to insist on the order is that the first two answers are free and the last two are not. Yet the pages that come up for this question start at the expensive end: of the five results on the first page, one is a shop, one sells replacement panels, one is a seven-year-old community answer and one is a user’s question on a Microsoft forum — which looks like documentation and is not. The documentation exists, it is published by the people who build the panels, and it contains the tests.

Notice what that list does that a symptom search cannot: it separates things by what they are rather than by what they look like on the day you noticed them. A dark pixel and a small black patch look identical in a photograph, and they have nothing in common — one is a fault in a single addressable point that a published tolerance may replace for nothing, the other is physical damage that the same document explicitly does not cover. Everything else on this page is about establishing which of the two you are looking at.

1. Put a white background behind it. A blank document, full screen. Apple’s rule does the work here: irregular shape, most visible on white, likely to be something that landed on the screen rather than something in it.
2. Clean it the way the maker says, not the way the internet says. Dell’s instruction is a soft, clean microfibre cloth “that is lightly dampened with water”, and its caution is the useful half: “Do not use benzene, thinner, ammonia or ammonia-based cleaners, abrasive cleaners or compressed air.” It also warns off detergents, “as they can leave a milky film on the monitor”. Unplug it first, and do not press: Dell writes that you should not “put pressure directly on the LCD screen as it may cause irreparable cracks”.
3. If it is still there, look at its edges and its size. A single sharp point is a pixel question. An area with a soft edge is a damage question. A line is a third thing again, and it goes to a vertical black line on a laptop screen.
4. Run the maker’s panel test and watch the mark on every colour. On a Dell laptop: restart, press F12 at the logo, choose Diagnostics; the screen then cycles through solid colours. Dell tells you what to look for on each: “On white : Look for any dark dots”. A mark that is there on every colour is in the panel; one that appears only on some images is not a mark at all.
5. Photograph it against white, with the date. The one thing that decides what happens next is whether it spreads, and that is a measurement over weeks. Two photographs, a month apart, in the same light.

One caution that belongs here rather than anywhere else, because this is the page people reach while holding a cloth. Pressing on the screen while cleaning is how a mark gets made. Dell says it twice, in two different documents: do not “put pressure directly on the LCD screen as it may cause irreparable cracks”, and, about the pixel remedies that circulate, “Applying pressure can crack the screen or damage internal components”. The mark you would be making is the one described in black pressure marks on a laptop screen, and it is not covered by anything.

A word about the question Google keeps attaching to this one: black spots in vision. They are not the same thing and the difference is easy to establish. A mark on a screen stays where the screen is: it does not move when your eyes move, it is in the same place for anybody else looking at the screen, and it disappears when the screen is off. Anything that behaves differently is not a computer problem, and this page has nothing useful to say about it — that is a question for a person who examines eyes, and neither source behind this page says a word on the subject.

And if what you are seeing is not a mark but the whole picture misbehaving — shivering, dimming, going out and coming back — the tests here are the wrong ones. Monitor flickering has the pair that fits that case, and a monitor with display problems covers the rest of what a screen can get wrong while the panel itself is perfectly healthy.

Not covered here. It will not name a product to clean your screen with. Dell describes the kind of tissue or solution to use and the things to avoid; a brand recommendation here would be an opinion dressed as a source.

It will not tell you what a panel costs. None of the four support pages read for this guide publishes a figure, and the sites that do sell the part.

And it will not answer a question about eyesight. It is built on two display makers’ documentation, and that documentation has nothing to say about eyes. What holds instead is simple: the statements that pixel anomalies are in many cases caused by a piece of foreign material trapped somewhere in the display or on the front surface of the glass panel, that foreign material is typically irregular in shape and usually most noticeable when viewed against a white background, and that material trapped within the screen must be removed by an Apple Authorized Service Provider or Apple Retail Store, are quoted from Apple’s article 102187; the definitions of a black line, spot or patch as internal crystal liquid cell damage whose shape or location might vary, and of an internal glass crack as cracked internal glass with liquid crystal inside the display panel along the crack, are quoted from Lenovo’s document HT104148; the description of a dark pixel as three subpixels permanently turned off and visible as a black dot on white or coloured backgrounds but not on black, the exclusion of dots that disappear when the screen is cleaned as dust, the instruction about what to look for on a white background during the colour cycle, the warning that applying pressure can crack the screen or damage internal components, and the answer that a stuck pixel stays stuck until the monitor is replaced, are quoted from Dell’s article 000126004; and the cleaning guidance — the anti-static screen-cleaning tissue or solution, the soft clean microfibre cloth lightly dampened with water, the caution against benzene, thinner, ammonia or ammonia-based cleaners, abrasive cleaners and compressed air, the warning that detergents can leave a milky film, and the instruction not to put pressure directly on the LCD screen as it may cause irreparable cracks — is quoted from Dell’s article 000124390.