Monitor test — dead pixels, stuck pixels & uniformity
Pick a pattern to open it fullscreen and look closely across the whole screen. Solid colours reveal dead and stuck pixels; the gradient reveals backlight bleed and uniformity issues; the checkerboard reveals scaling and sharpness problems. Nothing here is uploaded — every pattern renders locally in your browser.
Solid colours
Uniformity & sharpness
Click a pattern to open it fullscreen. In the test view: Space or a click moves to the next pattern, ←/→ step back and forward, Esc or the on-screen exit button leaves the test.
Stuck-pixel exerciser
Your system is set to reduce motion. The flasher still requires you to opt in below — nothing starts automatically.
Read more about how and why this works on the stuck-pixel fixer page.
Dead pixel vs. stuck pixel
These two terms get used interchangeably, but they describe different failures with different odds of fixing them.
- Dead pixel. The pixel (or one of its red/green/blue subpixels) receives no power and stays permanently black. It only becomes visible against a bright background — on a full-black screen it is invisible by definition, which is exactly why the black pattern above is still worth checking closely for other issues even though it can't reveal a dead pixel itself. Dead pixels are almost always permanent; there is no reliable software fix.
- Stuck pixel. The pixel is powered but a transistor is stuck holding one subpixel on, so it shows as a small dot of a fixed colour — commonly red, green, blue or white — against every pattern you display, including black. Stuck pixels are the type the flashing technique on this page is meant for, and it sometimes works.
- Hot pixel. A less common third case, usually discussed with camera sensors rather than displays: a pixel that is always at full brightness. On a monitor this looks similar to a stuck-white pixel.
How to inspect a screen properly
- Set your browser zoom to 100% and your display to its native resolution first. Scaling resamples the image before it reaches the panel and can hide or blur exactly the defects you're looking for.
- Clean the screen. A speck of dust or a fingerprint looks exactly like a stuck pixel from a normal distance and wastes a lot of time being investigated as one.
- Go through every solid colour fullscreen, including both grays and both saturated primaries and secondaries. A stuck pixel can be hard to spot against some colours and obvious against others.
- Check at a normal viewing distance first, then again close up. Dead and stuck pixels are usually invisible at arm's length on a large panel but obvious at 20cm.
- Scan systematically — corners, edges, then a grid sweep across the middle — rather than glancing at the whole screen at once. It is very easy to miss a single dot if you don't work through the surface deliberately.
- Repeat in a dark room for the black pattern specifically, to check backlight bleed and glow, which are much harder to see with the room lights on.
- Use the gradient to look for visible banding steps or a patch that is a noticeably different brightness than its surroundings.
- Use the checkerboard at native resolution to confirm the image is genuinely sharp — a blurry checkerboard where the pattern grid should be reveals the display is not actually running at native resolution, or that scaling is interpolating the image.
Backlight bleed vs. IPS glow
Both show up as extra brightness on an otherwise-black screen, and both get blamed on each other constantly, but they have different causes and different implications.
| Backlight bleed | IPS glow | |
|---|---|---|
| Cause | Light escaping around the LCD panel's edges or through an uneven diffuser/mounting pressure | An optical property of IPS-type panel construction itself |
| Where it appears | Usually along the frame edges, sometimes as a patch elsewhere | Corners of the screen nearest to you |
| Colour | Often a flat, slightly yellow or white glow | A softer silvery or golden sheen |
| Changes with viewing angle? | No — stays the same as you move | Yes — shifts, brightens or fades as you change your head position or viewing angle |
| Is it a defect? | A small amount is normal; a lot may be a return candidate | No — it is inherent to the panel type, present to some degree on every IPS-family panel |
The quick test: view the black pattern fullscreen in a dark room, then move your head or change your viewing angle. If the bright patches shift or fade, that's glow. If they stay exactly where they are regardless of angle, that's bleed.
Checking colour and brightness uniformity
Uniformity problems — patches that are visibly warmer, cooler, brighter or dimmer than the rest of the panel — are separate from dead pixels and backlight bleed, though all three get discovered the same way: a full-screen flat colour in a controlled room.
- Use the mid-gray patterns (25/50/75%) rather than pure white or black — uniformity deviations are much easier to see against a mid-tone than against either extreme.
- Look for large, soft-edged patches rather than sharp dots — a hard-edged dot is a dead or stuck pixel, not a uniformity issue.
- The gradient pattern is useful here too: a smooth ramp makes an unexpected step or blotch stand out much more than a flat fill would.
- Some colour non-uniformity is normal on every LCD panel, especially at the very edges; panel-to-panel variance and the cost of the display both affect how much is typical for a given price point.
Buying a used monitor — a quick checklist
If you can test in person before paying, work through these in order:
- Power it on and let it warm up for a couple of minutes before judging colour or brightness.
- Run every solid colour in this tool fullscreen and scan the whole panel for dots that don't match.
- Check the black pattern in as dark a room as you can manage, and move your head to separate bleed from glow using the test above.
- Run the gradient and look for banding, patches, or an abrupt brightness change.
- Run the checkerboard at the monitor's native resolution to confirm real sharpness, not an interpolated signal.
- Check the physical stand, ports, and buttons work, and that there's no visible scratch or crack in the panel itself.
- Ask about the return window before you pay, not after you notice a problem.
Honest limits of a browser-based test
- A browser can only ever show you what actually reaches the screen. It has no way to see anything the operating system's compositor, colour management, or the display's own image processing does after that point.
- Results depend on your browser zoom and display scaling being at 100%/native resolution. Anything else resamples the image before it reaches the panel and can hide exactly the fine defects this test is for.
- Some monitors process even solid colours. Dynamic contrast, local dimming and overdrive can all alter what a "flat" colour actually looks like on screen; there's no way for a web page to disable a monitor's own on-screen-display settings.
- This cannot measure refresh rate, response time, HDR peak brightness or colour accuracy. Those need either dedicated measuring hardware or test content beyond flat colours and simple patterns.
- The flasher is not guaranteed to fix anything. It is the standard attempt at unsticking a stuck subpixel, not a certain cure, and it does nothing for a genuinely dead pixel.
- What you type or click here never leaves your device. There is no account, no upload, and the test runs entirely in your browser.
Frequently asked questions
What's the difference between a dead pixel and a stuck pixel?
A dead pixel receives no power at all, so it stays black no matter what colour the screen is showing — it is usually permanent. A stuck pixel is still receiving power but is locked onto one colour (often red, green or blue, sometimes white), so it shows a coloured dot against every pattern instead of just being invisible on black. That distinction matters because stuck pixels sometimes respond to the flashing technique below; dead pixels essentially never do.
How do I check for dead or stuck pixels on my monitor?
Open each solid colour fullscreen and look closely across the whole panel, ideally from a normal viewing distance and then again up close. A dead pixel shows up as a tiny black dot on any colour except black itself. A stuck pixel shows up as a dot of a fixed colour that does not change as you switch patterns — check it against several different background colours to be sure it truly isn't moving or changing.
Can a stuck pixel be fixed?
Sometimes, not always. The flashing technique rapidly cycles the stuck subpixel's neighbours through different colours, and on some panels the repeated switching frees whatever was holding the transistor in one state. It has no effect on genuinely dead pixels, and it does not work on every stuck pixel either — some are permanent regardless of what you try.
Is backlight bleed a defect I can return the monitor for?
It depends on how much there is and on the seller's return policy, which this tool has no way to know. A small amount of light at the corners on a full-black screen in a dark room is normal on most LCD panels because the backlight cannot be perfectly masked at the edges. Bright patches, uneven blotches away from the edges, or bleed that is clearly visible in normal room lighting are worth raising with the seller while you are still inside the return window.
What's the difference between backlight bleed and IPS glow?
Backlight bleed is light escaping unevenly around the edges or in patches, and it looks the same regardless of your viewing angle. IPS glow is a property of IPS-type panels specifically: a soft, silvery or golden brightening in the corners nearest to you that shifts or disappears as you change your viewing angle or head position. Glow is an inherent characteristic of the panel technology, not a fault; bleed that stays fixed regardless of angle is more likely to be a manufacturing variance.
Why do I need to test at 100% zoom and native resolution?
Browser zoom and non-native display scaling both resample the page before it reaches the panel, which can blur or hide exactly the single-pixel defects and the fine checkerboard pattern you are trying to inspect. Set your browser zoom to 100% and your display resolution to the monitor's native resolution before running any of these patterns, especially the checkerboard.
Can this tool detect burn-in, refresh rate problems, or check HDR brightness?
No. Those all require either measuring equipment or specialised test content this tool does not attempt to provide. What it can do is show clean, correct solid colours, a gradient and a fine pattern so your own eyes can look for dead pixels, stuck pixels, backlight bleed and gross colour uniformity problems.
Is it safe to use the stuck-pixel flasher?
The flasher cycles through bright colours rapidly, and rapid flashing can trigger seizures in people with photosensitive epilepsy or cause discomfort even without a diagnosed condition. It is gated behind an explicit warning and an opt-in checkbox for that reason, it never starts on its own, and you can stop it instantly with Escape or a click at any time. If you have any history of photosensitivity, skip it.
Does this tool work on a phone or tablet screen?
The patterns render correctly on any screen, but fullscreen behaviour on mobile browsers is inconsistent — some restrict the Fullscreen API to video elements only. On a device where fullscreen is refused, the test still covers the browser's visible viewport, which is usually good enough to spot an obvious dead or stuck pixel, just with the browser's own address bar or status bar potentially still showing.