Understanding Display Panel Anatomy and Pixel Defects
A modern display panel relies on a dense grid of individual pixels to render images. Each pixel is composed of three distinct subpixels: red, green, and blue. By varying the light output of these three subpixels, the display can produce millions of different colors. When all three subpixels operate at full intensity, the pixel appears white; when all three are completely turned off, the pixel appears black.
Physical defects occur when these subpixels or their controlling transistors fail. This results in three primary categories of pixel anomalies:
- Dead Pixels: These occur when a pixel or its subpixels lose power entirely. Because they cannot light up, they show as black dots on white and bright screens. Dead pixels are the least likely to recover over time.
- Stuck Pixels: These happen when one or more subpixels remain frozen in an active state. They appear as fixed, colored dots that are clearest on their complementary color. Stuck pixels sometimes recover on their own.
- Hot Pixels: These are pixels where all three subpixels are stuck fully on, appearing as bright white dots on a black screen.
Preparing Your Device and Environment for Testing
To ensure an accurate visual inspection and avoid false positives, you must prepare both your physical environment and your device settings before launching the test:
- Clean the Screen: Gently wipe the screen to remove dust, smudges, and fingerprints. A tiny speck of dust on the glass looks exactly like a dead pixel at a glance and is the most common cause of false alarms.
- Adjust Device Settings: Raise your screen brightness to its maximum level. Turn off night mode, blue-light filters, and any active color filters, as these settings alter subpixel output and can mask defects.
- Control the Lighting: Dim the room lights or turn them off completely. A dark room makes it much easier to spot hot pixels, stuck subpixels, and backlight anomalies.
Navigating the Test Sequence
The Dead Pixel Test guides you through a sequence of 11 distinct screens designed to isolate different subpixel and panel issues. You can initiate the process by clicking Start fullscreen test.
If true fullscreen mode is unavailable on your browser or device, the tool displays the message: True full screen is unavailable here, so the test is running as an overlay.
To navigate through the test screens, you can use the following inputs:
- Keyboard: Press the left and right arrow keys (
← →) to switch between screens. - Touch Gestures: Swipe left or right to switch screens.
- On-Screen Controls: Click Previous screen or Next screen to move through the sequence, or click Exit to leave the fullscreen test.
The interface displays a HUD guide based on your input method: ← → switch · click a dot to mark it for desktop users, or Swipe to switch · tap a dot to mark it for touch devices.
Diagnostic Rules for Each Test Screen
| Test Screen | Screen Name | Diagnostic Purpose and Subpixel Rules |
|---|---|---|
| 1 | White | Scan the whole screen for dark or discolored dots. A pixel that stays black on white is likely dead. |
| 2 | Black | Scan for points of light (white or colored dots). White dots indicate hot pixels; colored dots indicate stuck pixels. |
| 3 | Red | The screen should be uniform red. A dark dot indicates a dead red subpixel; a glowing green or blue dot indicates a subpixel stuck on. |
| 4 | Green | The screen should be uniform green. A dark dot indicates a dead green subpixel; a glowing red or blue dot indicates a subpixel stuck on. |
| 5 | Blue | The screen should be uniform blue. A dark dot indicates a dead blue subpixel; a glowing red or green dot indicates a subpixel stuck on. |
| 6 | Cyan | Cyan lights green and blue subpixels. A dark dot indicates a dead red subpixel; a red dot indicates a red subpixel stuck on. |
| 7 | Magenta | Magenta lights red and blue subpixels. A dark dot indicates a dead green subpixel; a green dot indicates a green subpixel stuck on. |
| 8 | Yellow | Yellow lights red and green subpixels. A dark dot indicates a dead blue subpixel; a blue dot indicates a blue subpixel stuck on. |
| 9 | Mid gray | Exposes cloudy patches, faint vertical bands (dirty-screen effect), or image retention (ghosting). |
| 10 | Grayscale ramp | Displays a gradient from black to white. Visible steps or stripes indicate color banding from the cable or settings, not a pixel defect. |
| 11 | Checkerboard | Alternates tiles at a single-pixel pitch. Shimmering, moiré, or smeared areas indicate scaling issues rather than physical defects. |
Identifying False Positives and Non-Pixel Defects
Not every visual anomaly on a screen is a bad pixel. Use these rules to differentiate physical panel defects from other issues:
- Software vs. Hardware: A genuine physical defect stays at the exact same physical spot across different test screens and will never appear in a digital screenshot. If a dot appears in a digital screenshot, it is caused by software or content, not the display panel.
- Backlight Bleed: A pale glow bleeding in from the edges or corners of the screen in a dark room points to backlight bleed, which is a structural trait of the panel layers and backlight rather than an individual pixel defect.
- Banding and Scaling: Visible steps on the Grayscale ramp point to display cable or color configuration issues. Moiré patterns on the Checkerboard screen indicate that the display is not running at its native resolution, which can artificially mimic pixel defects.
Documenting Defects for Warranty Claims
If you spot a suspicious dot during the test, click or tap directly on it (either on the preview or during the fullscreen test) to mark and log its exact position.
The tool records these coordinates under the Marked spots heading. If no spots have been selected, the interface displays: Nothing marked yet. When a dot looks wrong, click or tap it — here on the preview or in full screen — and it is recorded with its position.
Coordinate System and Logging
Marked positions are calculated as percentage values relative to the top-left corner of the screen (0%, 0%). The logged list displays each entry in the following format:
#{index} · {screen} · {x}%, {y}%
For example, a spot marked on the red screen near the center might appear as:
#1 · Red · 50.2%, 49.8%
You can manage your marked list using these interactive options:
- To delete a specific marked spot, click its individual removal button labeled
Remove mark {index}. - To delete the entire list, click Clear all.
Closing or refreshing the browser page completely erases the current testing session and deletes all marked spots.
Manufacturer Policies and Standards
Warranty coverage for pixel defects varies by manufacturer, model, and region. Some brands offer a "zero bright pixel" policy for premium displays, replacing a panel over a single hot pixel. Other manufacturers follow ISO standards that permit a specific threshold of dark or stuck subpixels before a replacement is authorized. The location of the defect on the screen can also influence whether a claim is approved.
To back up a warranty claim or a return, document your findings by photographing the physical screen with the test color showing, using the marked coordinate list as a reference guide.
Privacy and Local Processing
The Dead Pixel Test operates entirely within your web browser. All test screens are drawn locally on your display, and your marked coordinates never leave the page. Nothing about your screen is measured, stored, or uploaded to any external server.
Frequently Asked Questions
What is the difference between a dead, a stuck, and a hot pixel? A dead pixel never lights up, so it shows as a black dot on white and bright screens and is the least likely to recover. A stuck pixel is frozen with one or more subpixels locked on, so it appears as a fixed colored dot — clearest on the complementary color — and is the type that sometimes recovers on its own. A hot pixel is stuck bright white and stands out on the black screen. Whichever type you find, a genuine defect stays at the same spot on every test screen and never shows up in a screenshot.
Why doesn’t the dot I see appear in my screenshots? A screenshot records the image your computer sends to the display, not the physical panel itself. A dot you can see that never appears in screenshots lives on the display side — that is the signature of a real panel defect. If a dot does show up in a screenshot, software or content is producing it: restart, update, or try another app before suspecting the screen.
How many bad pixels before a manufacturer replaces the screen? It depends on the brand, the model, and your region. Some premium lines replace a panel over a single bright pixel; others allow a few dark ones under industry standards, and where the defect sits on the screen can count too. That is why this test records every mark with its position — check the exact policy for your product, and run the test as soon as a new screen arrives so you are still inside the return window.
Can this tool fix a stuck pixel? No — this is a test, not a repair tool. Stuck pixels (never truly dead ones) sometimes fade with time or with tools that rapidly exercise the pixel, but those flashing tools carry a real photosensitivity risk and are a separate job. What this page gives you is a reliable diagnosis and documented evidence for whatever step comes next.
I found a dot — how do I confirm it is really a bad pixel? Wipe the screen gently first: a speck of dust looks exactly like a dead pixel at a glance. Then check the same spot across several test screens — a genuine defect stays at a fixed position and changes with the background: dark on white, bright on black, or colored on its complementary color. Lines, smudges, wide patches, or a glow along the edges are not pixel defects; those point at the panel layers or the backlight instead.