How to Test a Monitor
Six fields, in one order, with a reason for each position. This is the sequence ScreenTail's own guided test runs, and what each field can and cannot reveal.
Show white first, then black, then red, green and blue, then 50% gray. White is the only field where a pixel that is stuck off shows up; black is the only field where a pixel stuck on, or light leaking in at an edge, stands out; the primaries tell you how many pixels a speck really is; and gray is a whole-field judgment, so it comes last. Warm the screen up first, clean it, and work in a dark room.
Most people test a monitor by opening a few colored screens and looking for something wrong. That works, but the order you open them in decides what you are able to see at all. A pixel that is stuck off is invisible against black. A pixel that is stuck on hides in white. Show the fields in the wrong order and you can look carefully at all of them and still miss the fault.
This guide runs through the order ScreenTail’s guided Monitor Test uses, and gives the reason each field sits where it does.
Before you start
Four things change what a test shows, and all four are free to fix.
- 1
Warm the screen up. EIZO recommends that a monitor is already warmed up before testing, ideally for 30 minutes.
- 2
Clean the display. EIZO also recommends cleaning it first, because reflected light on a speck of dust looks exactly like a faulty pixel.
- 3
Darken the room. EIZO recommends carrying out the test in a dark room, which is the only way to judge dark areas precisely.
- 4
Sit at a normal distance. Dell assesses pixel faults at normal viewing distance, which it puts at about 35 to 50 cm for a standard monitor, and around 100 to 150 cm for large format monitors of 43 inches and larger.
This guide gives you no brightness setting, deliberately. No source we can cite states one, and inventing a number would be worse than leaving it out. Test at the brightness you actually work at, and write it down so the next check matches.
Set the computer to the display’s native resolution and the browser zoom to 100% as well. Anything else stretches the image, and single-pixel detail does not survive stretching.
Why the order matters
Two of the six fields are blind to each other’s faults. That is the whole reason there is an order at all.
Dell defines a bright pixel defect as one where all three subpixels in a pixel are permanently turned on, giving a bright white dot that is always visible, especially on dark backgrounds. A dark pixel defect is the opposite: all three subpixels permanently off, appearing as a black dot you can see on white or colored backgrounds.
So a dark fault needs a light field, and a bright fault needs a dark field. Neither one can find the other.
Run the primaries first and you finish with a list of specks and no way to tell how many pixels they stand for.
The primaries come third for the same reason. Dell’s definition of a pixel is three subpixels working together as a team: one red, one green, one blue. A pixel with a single faulty subpixel shows up on the field that lights that subpixel, so the same physical pixel can appear as a speck on red, on green and on blue. Read against the white and black fields you have already looked at, the primaries tell you how many pixels you are actually dealing with. Read first, they just give you a longer list.
Gray comes last because it is a different kind of judgment. It is not a hunt for a speck; it is a question about the whole field at once.
The six fields, in order
| Step | Field | Why here |
|---|---|---|
| 1 | White | The only field where a pixel stuck off is visible at all. |
| 2 | Black | The only field where a pixel stuck on, or light leaking in at an edge, stands out. |
| 3–5 | Red, green, blue | Read against steps 1 and 2, they show how many pixels the specks represent. |
| 6 | 50% gray | A whole-field judgment of evenness, so it comes after the speck hunts. |
The six values the guided test uses, shown as they are.
1. White
Look for dark specks. A dark pixel shows as a black dot against white, and a partly faulty pixel shows as a colored one, because the subpixels that still work are lighting up without the one that does not.
Scan in bands rather than staring at the middle, and cover the corners: a speck at the edge of the screen is the easiest one to miss and the most annoying one to live with.
2. Black
Now look for bright specks, and for something quite different: pale patches near the edges and corners. A bright pixel is always visible against black, by Dell’s own definition. A pale patch is not a pixel fault at all — it is light from the backlight escaping where it should not, which is why the Backlight Bleed Test exists as a separate check with its own guidance.
This is the step that needs the dark room most. In daylight, mild edge glow simply does not show.
3 to 5. Red, green and blue
Take each one in turn and note where the specks are, not just how many. Then compare the three lists with each other and with what you saw on white and black.
- A speck in the same position on all three primaries is one pixel.
- A speck on red only, say, is one faulty subpixel in a pixel that is otherwise fine.
- A speck you saw on white that appears on none of the primaries is worth a second look: it may be dust rather than a pixel.
6. 50% gray
Stop looking for specks. Step back, and ask whether the field is the same shade everywhere. Corners that look darker, a warm or cool cast on one side, or cloudy patches are what you are after. That is the job of the Screen Uniformity Test, which lets you switch between three gray levels, because some panels only show their unevenness at one of them.
What to do with what you found
| What you saw | What it usually is | Where to look next |
|---|---|---|
| A black dot on white | A pixel stuck off | Dead Pixel Test, full screen |
| A bright dot on black | A pixel stuck on | Dead Pixel Test, then each primary |
| A colored dot on white | One faulty subpixel | Dead Pixel Test, comparing the primaries |
| A pale patch at an edge | Backlight bleed | Backlight Bleed Test, dark room |
| Uneven tone across the field | Brightness or tint drift | Screen Uniformity Test |
| A faint shape from something you had on screen before | Image retention, on an OLED panel | OLED Burn-In Test |
Each finding has a guide of its own: Dead Pixel vs Stuck Pixel for a dot, Is Backlight Bleed Normal? for a pale edge, and the OLED burn-in guide for a shape that stays.
If you find a pixel fault and the display is new, this is the moment to check the maker’s own pixel policy rather than a general rule. Dead Pixel Warranty Policies quotes what Dell, ASUS, LG and Apple publish. Those policies differ by manufacturer, by product line and by region: Dell, for example, publishes allowances that depend on the display and on whether it carries Premium Panel Exchange, and other makers set their own. The number that matters is the one in your own maker’s published policy.
Makers disagree about stuck-pixel tools. In its guidelines for its own displays, Dell "strongly" recommends against pixel-fixing software and against pressing on the screen, saying such methods "may not work", can damage the display and "may void your warranty"; Lenovo's glossary says a stuck pixel has "the potential for correction through software methods". Other makers' terms may say something different. ScreenTail's Stuck Pixel Fixer flashes a small square of colors, so it opens only after a seizure warning, and it comes with no guarantee. Read the warranty terms for your own display before you try it; How to Fix a Stuck Pixel covers both sides.
What this test cannot tell you
A browser can show you a field. It cannot measure one.
- It cannot measure light. Nothing here reads brightness, contrast or color from your screen. You are judging with your eyes, in a room whose lighting changes the answer.
- It cannot see past the browser. Between this page and the glass sit the browser, the graphics driver, the display’s own processing and its settings. A result can come from any of them.
- It cannot separate dust from a fault. That is why cleaning the screen first matters; a speck that moves when you wipe was never a pixel.
- It cannot decide a warranty claim. It can only show you what to photograph and what to quote when you contact support.
What it does do is find the thing worth looking at, in the order that makes each fault visible, in about the time it takes to make a cup of tea.
Questions
Can a browser test damage my screen?
No. These tools paint plain colors and patterns, which is what every web page does. Nothing is written to the display, and nothing is stored on your computer.
How many dead pixels are normal?
That is set by the maker, not by any general rule, and it differs by product line and region. Dell, for example, publishes allowances that depend on the display and whether it carries Premium Panel Exchange. Check your own maker's published pixel policy before assuming a return will be accepted.
Does the room really matter?
Yes. EIZO recommends testing in a dark room, because a dark room is the only way to judge dark areas properly. A bright room hides edge glow almost completely.
I found a speck on red, green and blue. Is that three faults?
Usually it is one. A single pixel has a red, a green and a blue subpixel, so one faulty pixel can show on all three fields. Count the position, not the number of fields it appears on.
Why does the guide not tell me a brightness setting?
Because no source we can cite states one. Test at the brightness you actually work at, and write it down so your next check matches this one.
How this guide was made
The field order and the six values are taken from ScreenTail's own guided Monitor Test as it is built, not from a description of it. Everything about pixel definitions, viewing distance and test conditions is quoted from the manufacturer pages listed below, with the date each was retrieved.
Two things were left out on purpose. There is no recommended brightness setting, because no source we can cite states one. And there are no acceptable-defect counts here: those are set per manufacturer and per product line, so they belong in a warranty guide that quotes each policy with its date, not in a general guide.
- 01Dell's advice against pixel-fixing software and applying pressure (they may not work, can damage the display and may void the warranty), and that a stuck pixel stays stuck until the monitor is replaced (article last modified 06 Jul 2026): Dell, Display Pixel Guidelines — retrieved Sep 25, 2026.
- 02That stuck pixels have the potential for correction through software methods (a glossary Lenovo says is for reference only and may contain errors): Lenovo, What are Dead Pixels and How to Fix (glossary) — retrieved Sep 25, 2026.
- 03Definitions of a bright pixel defect, a dark pixel defect and a subpixel, and the normal viewing distance used to assess them: Dell, Display Pixel Guidelines — retrieved Sep 23, 2026.
- 04Warming the monitor up for about 30 minutes, cleaning the display, and testing in a dark room: EIZO, Monitor Test — retrieved Sep 23, 2026.
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Vivek Kumar runs ScreenTail from New Delhi. He has worked with computers for about 25 years and studied Computer Science. He is not a display engineer or a color scientist, and each guide says where its facts come from so you can check them.