Dead Pixel Test

Put a solid color on the monitor you want to check and step through all eight

The monitor drawing above is the test screen. Move this browser window to the monitor you want to check, then press Start full-screen test or the F key, and the whole screen fills with the chosen color. Click the screen or press → for the next color, and press Esc to finish. Colors change only when you move on, so you can stay on one color as long as you need and look into every corner.

When you spot something suspicious, press M or switch on Mark spot in the control bar, then click that place. A numbered ring appears around the dot, and when you finish, the Suspect spots log below lists its position (x and y pixels counted from the top left of the screen) and the colors it showed up on. Clicking the same place on another color adds that color, so you can compare at a glance which backgrounds reveal the dot. Use Copy log and paste the text straight into a message to the seller or manufacturer.

Why run a solid-color check as soon as a new monitor arrives

A monitor panel is made of millions of pixels, and manufacturers say up front that a few defects can occur. Acer's user manual for the PM161Q B, for example, states that "the LCD screen has 99.99% or more effective pixels" and that it may include blemishes of 0.01% or less, such as a missing pixel or a pixel lit all the time. A 1920 × 1080 screen has 2,073,600 pixels, so 0.01% is about 207. Whether you can get a replacement therefore depends less on that sentence than on the pixel policy and warranty period set by the seller and manufacturer, and what matters is finding and documenting the dots within that period.

• Right after you receive a new monitor or laptop: EIZO guarantees zero bright subpixels for 6 months after purchase on some models. Warranties like this have a time limit, so test on the day it arrives.
• When you inspect a used monitor or laptop in person: open this page in that device's browser and step through all eight colors in a few minutes. If you spot a dot with the seller there, log its position with the marking feature.
• When a small speck on the screen keeps bothering you: sorting out whether it is dust, an always-on pixel or something visible on one color only tells you whether to wipe the screen or contact support.
• After a repair or replacement: compare against the x and y positions of your first log to see whether the same dot is still there or a new one has appeared.
• For photo, video and design work: look at the gray screen first for broad blotches and a color cast to one side. Setting brightness and color accurately takes a measuring instrument.

How to use it

1. Prepare: check the screen surface for dust and make sure windows and lamps don't reflect in it. Switch off anything that changes color or brightness, such as night mode, blue-light filters and auto-brightness, and note your original settings. Keep brightness at the level you normally use.
2. Move the window: if you have several monitors, drag the browser window to the one you want to check. The line under the monitor drawing shows that screen's resolution and scale, so you can confirm it is the right one.
3. Pick a color and start: choose the starting color in the Test colors row and press Start full-screen test. Starting with black is a good idea, because stuck-on dots are easiest to see there.
4. Scan the screen: sweep from the top left to the right, then work down line by line to the edges. Click the screen, press → or Space for the next color, ← for the previous one, and 1 to 8 to jump straight to a color.
5. Mark a dot: when you see a suspicious spot, press M and click it. If the same dot shows on other colors, click its ring again; click once more to remove a color you added by mistake. A dashed ring is a dot you haven't marked on the current color yet.
6. Hide the control bar: when the mouse stops, the control bar and the cursor disappear after 2.6 seconds and return when you move it. Press H to hide or show them right away. On a touch screen, the first touch after hiding only brings the bar back and does not change the color.
7. Finish and keep the log: when you return with Esc or Exit, every color shown for at least one second is checked in the Test colors row, and the suspect-spot log keeps each position and the colors it appeared on. The log isn't saved, so use Copy log to keep it.

What each of the eight colors reveals

Each pixel mixes the light of three subpixels, red, green and blue. A solid-color screen turns all of them off, all of them on, or just one kind on, so a subpixel that is stuck on or off stands out against its neighbors. EIZO's monitor test guide says the same: colored dots on a black screen are subpixels that stay on, a black dot on a white screen is a missing pixel, and a black dot on a red, green or blue screen is a missing subpixel of that color.

This is also why a single white screen isn't enough. According to EIZO's pixel policy document, blue is the color that looks darkest of the three, so a blue subpixel that is off shows up only as a slightly yellow dot on white. Green looks brightest, so a dot with green off appears magenta-tinted and is comparatively easy to see on white. Stepping through red, green and blue one by one lets an off subpixel show as a black dot on its own color.

The color combinations in the table assume the common layout with one red, one green and one blue subpixel per pixel. Some panels arrange subpixels differently, and the color you see by eye can't tell you which part failed or why.

How many dead pixels is too many: defect types and ISO 9241-307

Dot defects on a screen are usually sorted into four types. The table below gives the definitions from EIZO's pixel policy document and the allowed counts for ISO 9241-307:2008 Class 1, the international standard that document describes. The counts apply to one 1920 × 1080 monitor (about 2 million pixels).

EIZO's document calls Class 1 the one most often referred to and summarizes it as allowing up to 4 pixel faults and up to 10 sub-pixel faults on a monitor with 2 million pixels. EIZO's own standard in the same document is stricter: current models have 0 pixel defects and at most 5 subpixel defects in total. The bright subpixels covered by the zero-bright-subpixel guarantee are those visible in an office brighter than 500 lx from a distance of more than 35 cm.

Whether you actually get a replacement is decided by the warranty policy of the shop and the manufacturer, not by the standard. Read the product page's "zero dead pixel" guarantee terms first: whether it covers only bright dots, from how many dots it applies, and within how many days you must apply. Then sort the dots you marked with this tool into the types above and compare. For monitors with other resolutions, check the standard itself or the manufacturer's documents for the allowed counts. As a reference, the resolution line on the page lets you count pixels: 2560 × 1440 is 3,686,400 pixels (about 3.7 million) and 3840 × 2160 is 8,294,400 pixels (about 8.3 million).

How to log a suspect dot and contact support

The starting point is whether the same dot stays in the same place on several colors. The eight boxes on a log row show the colors on which you marked that dot. If the black box is filled, suspect a pixel or subpixel that stays on (Type 1 or 3a); if only white, red, green or blue are filled, suspect an off pixel or subpixel (Type 2 or 3b), or dust, first. When you write to the seller or manufacturer, include the following.

• The text from Copy log: it holds the date, resolution and scale, whether the test was full screen, the colors seen, and each dot's position and colors. The x and y values count from the top left pixel of the screen, which is 0.
• Model name, serial number and purchase date, plus the connection type (HDMI, DisplayPort, USB-C).
• Two photos: one showing the whole screen and one close to the dot. Focus, exposure and moiré patterns can make a small dot vanish or create patterns that aren't there, so send the x and y from the log along with them.
• The conditions you checked: whether the dot remains after wiping the surface, and whether it is in the same place with another computer or cable.

Screenshots don't capture dots. A screenshot saves the image data the computer sends to the display and says nothing about the physical state of the panel. Conversely, if the same dot also shows in a screenshot opened on another device, look first at the image being displayed rather than at a panel defect.

Telling a dead pixel from dust, reflections and backlight bleed

• Dust and debris: on a white screen they look like black dots. Wipe the screen as the manufacturer's cleaning instructions say and look again on the same color. Don't scratch with a fingernail or press and rub the spot.
• Reflections: a bright spot from a window or lamp moves when you move your head. A pixel defect stays on the same pixel wherever you look from.
• Backlight bleed at the edges: on a black screen, wide brightening along the corners or edges is a different phenomenon from a small dot defect. It changes with viewing angle and room brightness, so note its position and size separately and don't count it as a dot.
• Image retention: manuals note that after the same image is shown for a long time, a faint outline of it may remain when the picture changes. If it looks like a broad pattern on a solid color, record it separately from dot defects.
• The cursor: it hides when the mouse stops. While Mark spot is on, a crosshair cursor stays visible so you can aim.

When full screen doesn't work, on phones and with two monitors

Browsers allow full screen only at the moment you click or press a key, and they leave it when you press Esc or F11 or switch to another tab or app. When you come back, press Start full-screen test again.

Safari on iPhone does not support full screen for web page elements (iPad does). In that case this tool opens as an in-window test that covers the window, and the control bar says it covers only n% of the screen. Leave the areas hidden by the address bar and status bar out of what you checked. Browsers inside messenger or social apps may block full screen, so reopen the page in your default browser.

With two monitors, test one at a time. Move the window to the monitor you want to check and start, and that monitor goes full screen while the resolution line shows its values. In mirror mode the same color appears on both screens, so write down which monitor you actually looked at.

The resolution on that line is the screen size the browser reports multiplied by the scale (devicePixelRatio). The scale includes both the operating system's display scaling and browser zoom, so if you changed the scaling to "more space" or zoomed the browser, the number can differ from the panel's real resolution. Set browser zoom to 100% and compare it with the value in your operating system's display settings.

Common mistakes

• Stopping at one white screen: a dot with a blue subpixel off is almost invisible on white. Go on through red, green and blue.
• Turning brightness all the way up: look at your usual brightness and don't change it while switching colors, so every color is compared under the same conditions.
• Mistaking the in-window test for full screen: if the control bar shows "n% of the screen", you have checked only part of it.
• Sending only photos: photos sometimes don't capture the dot, so send them together with the logged position.
• Leaving a flashing "repair" screen on for a long time: this tool has no such feature. Rapid flashing can trigger photosensitive seizures, and the web accessibility guideline (WCAG 2.3.1) says to avoid more than three flashes per second. If you are still under warranty, keep a log and contact the seller or manufacturer first.

Limitations

• This tool fills the screen with solid colors and organizes the positions you mark. It does not read the panel to find defects automatically or to decide how many there are.
• Not finding a dot doesn't guarantee a perfect screen. Very small subpixel defects, pixels that only flicker now and then, and hidden areas can be missed.
• The colors on screen are what the browser draws, so they depend on browser color management and operating system settings. Brightness, color accuracy, response time and refresh rate are not measured.
• The x and y positions can be off by 1-2 pixels depending on the scale, so treat them as "around here".
• The log lives only in the tab that is open now and is neither saved nor sent anywhere. Use Copy log before closing the page.

Sources

• 01EIZO Monitor TestDefects seen on black, white, red, green and blue; uniformity on a gray screen; display differences due to browser color management
• 02EIZO Pixel Policy (2016-04-12, PDF)Defect Types 1, 2, 3a and 3b; ISO 9241-307:2008 Class 1 allowances (1920 × 1080); conditions of the zero-bright-subpixel guarantee (500 lx, 35 cm); colors seen on white when a blue or green subpixel is off
• 03MDN: Fullscreen API GuideFull screen can be requested only inside an event handler; Esc and F11; it ends when you switch tabs or apps
• 04MDN: Element.requestFullscreen() browser compatibilitySafari on iOS: only available on iPad, not on iPhone
• 05MDN: Window.devicePixelRatioRatio of physical pixels to CSS pixels; page zoom changes the value
• 06Acer PM161Q B User Manual (2023-08-08)LCD screen with 99.99% or more effective pixels, possible blemishes of 0.01% or less, afterimage after long display of the same image
• 07W3C: Understanding WCAG 2.2, 2.3.1 Three Flashes or Below ThresholdThe criterion to avoid content that flashes more than three times in any one second

Sources checked 2026-10-20. The ISO 9241-307 allowances are the values quoted in EIZO's document, not the text of the standard, and actual replacement terms follow the policy of the seller and manufacturer.

Frequently asked questions

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