What this dead pixel test does
This dead pixel test fills your whole screen with one flat color at a time, so a faulty pixel has nowhere to hide. Press "Start screen test" and the page goes full size and steps through black, white, red, green, blue and gray. A dark dot on white, a bright dot on black or an odd-colored dot on red, green or blue is a pixel fault.
Around the colors sit tools most screen test pages leave out: a locator grid that labels the screen like a spreadsheet, a calculator that compares your defect count with the commonly cited ISO pixel-defect classes, extra screens for gradients and backlight bleed, and a stuck pixel fixer that stays off until you confirm a photosensitivity warning.
How to use the dead pixel test
- Prepare the screen. Wipe it with a dry microfiber cloth, raise the brightness, switch off night light or color filters, and dim the room for the black screen.
- Choose the screens. "Screens to show" offers "Essential: 6 screens" or "Full: 15 screens", which adds cyan, magenta, yellow, two more grays, two step charts and two gradients.
- Start. Press "Start screen test", or click a tile to begin on that color. The page goes fullscreen where the browser allows it.
- Move through the screens. Click, tap, or press Space or the right arrow for the next one. The left arrow or a right-click goes back, keys 1 to 9 jump, and on a touch screen you tap the left edge for back or swipe.
- Scan slowly, corner by corner. Press G to cycle the locator grid. Columns are lettered and rows numbered, so "C7" names one cell.
- Leave. Press Esc, use the Exit button, or press and hold on a touch screen. A small bar with hints shows at the start, after each change and when the mouse moves; H pins it.
- Count and compare. Enter what you found under "Count what you found and check the class". "Auto-advance" can change screens every 3, 5 or 10 seconds so you can stand back.
Dead, stuck and hot pixels
A pixel is typically built from red, green and blue subpixels, and faults are named by what those subpixels do.
| Fault | What is wrong | What you see | ISO type |
|---|---|---|---|
| Dead pixel | All subpixels stay off | Black dot, clearest on white | Type 2 |
| Hot pixel | All three stay on | White dot, clearest on black | Type 1 |
| Stuck subpixel | One or two stay on or off | Colored dot, such as red or cyan | Type 3 |
The colors tell you which subpixel is at fault. On the red screen only red subpixels should glow, so a green, blue or white dot means another subpixel is stuck on, and a black dot means the red one is dead. Cyan, magenta and yellow each need two subpixels, so they expose a missing red, green or blue. Not every dot is a fault: dust on white looks like a dead pixel until you wipe it away.
| Screen | What it reveals | A fault looks like |
|---|---|---|
| Black | Pixels stuck on, backlight bleed | A bright or colored dot, or a glowing edge |
| White | Dead pixels, dirt, color tint | A dark dot, or a colored dot |
| Red, green, blue | A stuck or dead subpixel of another color | A dot that is not the screen color |
| Cyan, magenta, yellow | A missing red, green or blue subpixel | A dot with a different hue |
| Gray 25%, 50%, 75% | Uneven brightness, clouding, tint | A patch that is lighter, darker or tinted |
Backlight bleed and IPS glow
On an LCD, light can leak past the edges of a black screen, and two things cause it. Sit back in a dim room with the black screen up, then move your head slowly. A haze that shifts or fades is IPS glow, a property of the panel type. A bright patch locked to the same edge or corner is backlight bleed, which can come from uneven pressure on the panel. A little of either is common, so judge by whether it bothers you in dark scenes. OLED screens have no backlight, so use the gray screens to look for uneven wear instead.
Gradients and banding: a worked example
The gradient screens draw a black-to-white ramp by giving each screen column its own level. Across a 1,920-pixel-wide screen an 8-bit ramp has 256 levels, so each should cover 1,920 ÷ 256 = 7.5 pixels. On a 3,840-pixel-wide screen each covers 15.
That is your yardstick. Stripes about that wide are the smallest steps the format allows; much wider stripes mean fewer than 256 levels reach your eye. Suspects are a 6-bit panel without dithering, a limited color range, a color profile or the graphics driver. Color management in your browser or operating system can also remap the ramp's exact values.
The step charts help too. "Near-black steps" shows levels 0 to 15 and "Near-white steps" shows 240 to 255. If the first three bars look identical, brightness, contrast or range settings are crushing shadow detail.
Counting defects and the ISO classes
The older ISO 13406-2 standard sorted panels into four classes by faults allowed per million pixels, and ISO 9241-307 later replaced it. The figures below are the ones manufacturers and retailers most often quote. ISO sells the standards' full text, and some maker policies differ from this table, for example by splitting Type 3 into always-lit and always-dark subpixels, so treat it as a guide and read the maker's own policy.
| Class | Type 1 (always lit) | Type 2 (always dark) | Type 3 (stuck subpixel) |
|---|---|---|---|
| I | 0 | 0 | 0 |
| II | 2 | 2 | 5 |
| III | 5 | 15 | 50 |
| IV | 50 | 150 | 500 |
The calculator scales those rates to your panel. A 1920 × 1080 screen has 2,073,600 pixels, or 2.0736 million. Class II allows 2 × 2.0736 = 4.1472 Type 1 defects, so four pass and five do not; Type 3 allows 5 × 2.0736 = 10.368. Limits are not rounded, so the table shows 4.1 and 10.4. At 2560 × 1440 the Class II limits are 7.4, 7.4 and 18.4, and at 3840 × 2160 they are 16.6, 16.6 and 41.5.
Choose your size under "Panel resolution" or "Custom size", enter your counts, and each class shows "within" or "over". "Copy report" or "Download report" saves the result. Maker policies often also limit clusters of neighboring defects, which this tool does not check, and they vary: some promise zero defects, some follow Class II, some set their own numbers.
What to do if you find a defect
Write down the color screen where the dot shows, its grid cell and how many you found, then photograph the screen with the test color up. Next, check the return window, because a retailer's return is often quicker than a manufacturer's warranty claim. Find the maker's pixel policy on its support site and compare your counts with it, using the calculator above as a rough guide. Then contact the seller or maker with your notes and photos. If a policy sets a zero-defect or low limit, say so and ask for a replacement. Try the fixer only after you have documented the fault, in case the dot moves or changes.
Testing a new monitor, laptop or phone
- Monitor buyers. Test on day one, inside the return window. Run all 15 screens, note grid cells such as "H6" for each fault, and photograph them.
- Used laptop buyers. Run the test with the seller present at full brightness. Check gray 25% for pressure marks near the hinge and edges.
- Phone repair technicians. After a screen swap, run the essential set in both orientations and at low brightness, where uneven tint shows most.
- IT teams. Run refurbished units and attach the downloaded report to the ticket.
Can a stuck pixel be fixed?
A dead pixel almost never comes back, because the fault is in the hardware. A stuck or hot pixel sometimes does, and nobody can promise it. The stuck pixel fixer cycles red, green, blue, white and black in a small square that you drag over the faulty pixel, or across the whole screen if you pick "Whole screen".
Run it for the full minute, then recheck the color screens, and repeat a few times. If nothing changes, the fault is probably permanent and the warranty is the better route. This fixer flashes slowly for safety, so it may need more runs than faster tools, and we have no published success rate to quote. Pressing on the spot with a soft cloth is sometimes suggested, but it can cause new damage and void a warranty.
Photosensitivity and safety
The fixer stays off until you tick the box in the warning dialog. It never changes color more than three times per second. The web accessibility guidelines (WCAG 2.3.1) say content should not flash more than three times in any one-second period unless the flashes are small or dim enough to fall under its thresholds. A flash counts as a pair of opposing changes, so three changes a second is at most about one and a half flashes. Staying under the limit lowers the risk but does not remove it.
The default flash area is a small square, the fixer stops itself after 60 seconds, and Esc, a tap or the Stop button ends it at once. It also ends if the tab is hidden, and it drops to one change per second when your system asks for reduced motion. Do not use it if you or anyone nearby may be sensitive to flashing images.
Tips and common mistakes
- Clean first. Dust and fingerprints imitate dead pixels. A real fault is a sharp dot that a cloth cannot move.
- Look closely. One pixel on a 27-inch 2560 × 1440 monitor is about 0.23 millimeter across, so get near the glass or use a phone camera in macro mode.
- Skip screenshots. A screenshot captures the signal, not the panel, so a dead pixel never appears in one.
- Retest later. Faults can show up days after purchase, so run the test again inside the return window.
- Check other hardware. Try the keyboard tester, the mouse test or the click speed test.
Privacy and limitations
The test paints colors and reads nothing back. Your choices under "Screens to show", "Auto-advance", "Locator grid" and the fixer options are kept in this browser's local storage. The resolution and counts you enter live in session storage and vanish when the tab closes. Nothing is uploaded. The browser's screen size, pixel ratio and color depth are shown to you, and they enter a report only if you copy or download one. While a test is open the page asks the browser to keep the screen awake, where supported.
This is a visual check, not a measurement. A browser cannot read brightness, color accuracy, response time or true panel bit depth, and HDR or a television's picture processing can change how a flat color looks. Remote desktop and virtual machines show a copy of the screen, not the panel. On iPhone, Safari offers no fullscreen for a page like this, so the test fills the visible page and browser bars may remain. Class comparisons are informational, not a certified inspection.
Frequently asked questions
How do I check for dead pixels on my screen?
Clean the screen, raise the brightness and press Start screen test so the page goes full size. Step through black, white, red, green and blue, and look at each one from close range. A black dot on white is a dead pixel, a bright dot on black is a hot pixel, and a colored dot is a stuck subpixel. Press G to overlay the locator grid so you can note where each dot sits.
What is the difference between a dead pixel, a stuck pixel and a hot pixel?
Every pixel has red, green and blue subpixels. A dead pixel has all of them off, so it shows as a black dot, clearest on white. A hot pixel has all of them stuck on, so it is a white dot, clearest on black. A stuck pixel has one or two subpixels frozen on or off, so it shows as a red, green, blue, cyan, magenta or yellow dot. Stuck and hot pixels sometimes recover; dead ones rarely do.
Can a stuck pixel be fixed?
Sometimes. A stuck or hot pixel may respond to flashing colors over the spot, so the stuck pixel fixer cycles colors in a small square that you drag over it for up to 60 seconds. Run it a few times and recheck with the color screens. A dead pixel is a hardware fault and almost never recovers, and no method is guaranteed. If the screen is under warranty, document the fault before you try anything.
How many dead pixels are acceptable under warranty?
It depends on the maker. The older ISO 13406-2 standard and its successor ISO 9241-307 group panels into classes, and makers commonly quote Class II, which is usually given as 2 always-lit, 2 always-dark and 5 stuck-subpixel defects per million pixels. On a Full HD screen that scales to roughly 4, 4 and 10. Some makers promise zero, some split the subpixel limit or count clusters, so read the pixel policy before you claim. The calculator on this page compares your count.
What is backlight bleed, and how is it different from IPS glow?
Both are light showing on a black LCD screen. Backlight bleed is light leaking past the edges or corners, and it stays in the same place however you view the screen. IPS glow is a soft haze that shifts or fades as you move your head. Show the black screen in a dim room and move slowly to tell them apart. OLED panels have no backlight, so neither applies to them.
Is the flashing stuck pixel test safe?
Flashing lights can trigger seizures in people with photosensitive epilepsy, so the fixer stays off until you confirm a warning. It changes color at most three times per second, uses a small square by default, stops after 60 seconds, and ends at once with Esc, a tap or the Stop button. It slows to one change per second if your system asks for reduced motion. Skip it if anyone nearby may be sensitive to flashing.
Does the dead pixel test work on a phone or iPhone?
Yes. Tap for the next color, tap the left edge to go back, swipe left or right, and press and hold to exit. Android browsers can usually go fullscreen. iPhone Safari does not offer fullscreen for a web page like this, so the test fills the visible page instead and the browser bars may stay on screen. Hiding the toolbar in Safari's aA menu helps on recent versions.
Does the test store anything or damage my screen?
It only paints flat colors, which is ordinary use for a display and should not harm a working screen. Do not leave a bright static color on an OLED panel for long stretches. Nothing is uploaded. Your options stay in this browser's local storage, and the defect counts you enter stay in session storage until the tab closes. The page asks the browser to keep the screen awake while a test is open, where supported.