Monitor test - colour, uniformity and backlight bleed
Go fullscreen and darken the room. Browser chrome and a taskbar cover the edges of the panel, which is exactly where backlight bleed shows.
The stuck pixel exercise slowly alternates colours. If you are sensitive to flashing light, do not use it.
Click the field or press the arrow keys to move between tests, F for fullscreen, Escape to leave it. Everything runs in your browser.
Why a flat colour field finds what a normal page hides
Panel faults are almost invisible against ordinary content, because text and pictures give your eye something else to look at. Fill the screen with one flat colour and there is nowhere for a fault to hide - a single bright dot on pure black, or a corner glowing where it should be dark, is unmistakable.
How to run the test properly
- Go fullscreen. Browser chrome and the taskbar cover the edges of the panel, and the edges are exactly where backlight bleed appears.
- Turn the lights down. Bleed and clouding can only be judged fairly in a dark room. In daylight a poor monitor looks acceptable and a good one looks perfect.
- Clean the screen first with a dry microfibre cloth. A surprising share of reported dead pixels are specks of dust, and the blue field makes those obvious.
- Sit square to it. Most LCD panels shift in colour and brightness off-axis; that is the technology, not a fault.
- Step through every field with the arrow keys.
What each fault looks like
| What you see | What it is |
|---|---|
| A black dot on white | A dead pixel - the pixel receives no power |
| A coloured dot on black | A stuck subpixel - sometimes recoverable |
| Glow at the edges or corners on black | Backlight bleed - light escaping past the panel |
| Soft grey patches on a dark field | Clouding, called IPS glow on IPS panels |
| A colour cast on grey | White balance is off - usually fixable in the monitor menu |
| Visible steps in the gradient | Banding, from a panel with limited colour depth |
| Blurred lines on the grid | Not running at the native resolution |
Dead, stuck, and which is worth pursuing
A dead pixel stays black on every field and cannot be revived. A stuck pixel shows a fixed colour and can sometimes be freed by driving it repeatedly through its range - which is what the stuck pixel exercise on this page does. Leave it running over the affected area for ten minutes or more. It is a matter of luck rather than a reliable repair.
Before claiming under warranty, check the manufacturer policy. Most set a threshold - a certain number of dead pixels, or any dead pixel in the central zone - and a single one near the edge is often deemed within specification.
A note on the flashing exercise
The stuck pixel exercise alternates colours deliberately slowly, at two changes a second. That is below the rate associated with photosensitive seizures; many similar tools flash as fast as the display allows. It never starts on its own, and it is disabled entirely when your system is set to reduce motion. If you are sensitive to flashing light, do not use it - and note that a slower cycle is no less effective, since freeing a stuck pixel depends on how long it runs rather than how fast it flashes.
Related checks
Our dead pixel test concentrates on that single fault, the refresh rate test measures the frames a second your monitor presents, and screen resolution tells you whether you are running at the panel native resolution - which is what the sharpness grid here is checking.
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