Check for dead pixels, bright spots and dark spots
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Monitor problems? Try these fixes
If a pattern above showed something wrong, work through these in order — cheapest and most reversible first:
- Clean the screen and look again. Dust, fingerprints and dried spray marks mimic stuck pixels and dirty-screen effect exactly. Wipe with a dry microfibre cloth, then re-run the black and white patterns before concluding anything is broken.
- Reseat the cable, then try a different one. Flicker, colour casts, dropouts and banding are cable problems as often as panel problems. Push both ends home; if it persists, swap the cable and try another port. A cable running below the bandwidth your resolution and refresh rate need will quietly reduce colour depth or chroma rather than fail outright.
- Check the OS display settings. Confirm the resolution matches the panel's native one and the refresh rate is set to its maximum — Windows and macOS both quietly drop to lower values after a driver update or a new cable. Compare against the Refresh rate reading above.
- Turn off the monitor's picture enhancements. Dynamic contrast, sharpness above the neutral setting, eco or ambient-light modes, and aggressive overdrive all distort these patterns. Reset the monitor to factory defaults and retest before adjusting anything by hand.
- Try the panel on another machine. This separates the monitor from the graphics card, driver and cable in one step. If the fault follows the monitor, it is the monitor; if it stays with the machine, it is not.
- For a stuck pixel, try exercising it. A pixel stuck lit sometimes recovers after cycling rapidly changing colours over it for a few minutes — the Ghosting and colour patterns will do that. It does not work on a truly dead pixel, which stays black because it receives no power at all.
- Record what you found before claiming warranty. Use Copy report above for a written list of which patterns failed. Manufacturers apply a dead pixel policy with a minimum fault count, so the specifics matter.
Frequently asked questions
What does Monitor Test Online do?
It fills your screen with test patterns that make display faults obvious — solid colours for dead and stuck pixels, pure black for backlight bleed, grey ramps for banding, and moving blocks for ghosting. Step through them full screen, mark each one pass or flagged, and copy a report of what you found. Everything runs in the browser; nothing is uploaded.
How do I check for dead pixels?
Run the solid colour patterns full screen and look closely at each one. A dead pixel stays black on every colour. A stuck pixel stays lit in one colour, so it shows as a bright red, green or blue dot on the black pattern. Clean the screen first: dust and smears look exactly like faults until you wipe them off.
What is backlight bleed and how do I test for it?
Backlight bleed is light leaking around the edges of an LCD panel, visible as bright patches or clouding on a black screen. Use the Backlight bleed pattern in a dark room, let your eyes adjust for a minute, and look at the corners and edges. Some bleed is normal on IPS panels; large bright patches are not.
Why does my refresh rate read lower than my monitor's rating?
The measured figure is how fast the browser is actually being given frames, which is not always the panel's maximum. Common causes: the refresh rate is set lower in your OS display settings, the browser window is on a different monitor than you think, a variable-refresh-rate feature is throttling to save power, or a laptop is on battery. It is also capped by what the browser will do in a background or partly hidden tab.
What is banding, and what should the grey ramp look like?
A greyscale ramp should fade smoothly from black to white with no visible steps. If you can see distinct bands or contour lines, the display or the graphics pipeline is quantising the gradient. That is common on 6-bit panels using dithering, on aggressive display presets, or over a bandwidth-limited cable mode. Try a different preset or cable before assuming the panel is at fault.
What is ghosting and how does this test show it?
Ghosting is a trail behind moving objects, caused by pixels changing colour slower than the image moves. The Ghosting pattern slides blocks across the screen at several speeds, so you can look for smearing or a faint trail behind each block. If your monitor has an overdrive or response-time setting, this pattern is the one to use while adjusting it; too much overdrive produces a bright trail instead, called inverse ghosting. See the dedicated monitor ghosting test page for a deeper explanation.
Does this work on a phone, laptop or TV?
Yes. Any screen that runs a modern browser can display the patterns, and the full-screen view uses the whole panel. The measured resolution reflects what the browser reports in CSS pixels along with the device pixel ratio, so on a high-density phone or a scaled laptop display those two numbers together describe the real panel.
Is a dead pixel covered by warranty?
It depends on the manufacturer's dead pixel policy, which usually sets a minimum number of faulty pixels before a panel qualifies for replacement, often several, and sometimes with stricter limits for pixels near the centre. Use the report from this page to record exactly what you found and where, then check the policy for your specific model before starting a claim.
Can this test check screen uniformity or brightness evenness?
Yes — the Uniformity set includes a 9-zone pattern and low-brightness grey fields. Display each full screen in a dim room and look across the panel rather than at one spot: uneven brightness shows up as visibly darker or brighter patches, most often in the corners or near the edges, and is a separate issue from backlight bleed, which only shows on pure black.
Can this test calibrate my monitor or measure colour accuracy?
No — it's a visual pass/fail check, not a colorimeter. The patterns will show obvious problems like banding, a colour cast, or gamma that's clearly off, but getting your monitor calibrated to a specific standard needs a hardware colorimeter and calibration software. Use this tool to sanity-check a panel or confirm a calibration looks right, not to replace one.