A dead pixel test only checks one thing. A panel can pass it and still have light pouring out of its corners, crushed blacks, visible banding in gradients, or a backlight that is noticeably brighter on one side. This guide runs the full set of checks in the order that makes sense — each one takes a minute, they need nothing but a browser, and together they tell you whether a screen is worth keeping, returning or claiming on.
On this page
- How should you prepare before testing an LCD screen? — the conditions that make the results mean anything
- How do you test an LCD screen for dead pixels? — the first check, and the one with the clearest pass or fail
- How do you check for backlight bleed and clouding? — the most common LCD complaint, and the one with no software fix
- How do you test contrast and black levels? — whether the panel actually separates the shades it claims to
- How do you check colour uniformity and banding? — the tests that expose an ageing or uneven backlight
- How do you check resolution, scaling and refresh rate? — the settings that make a good panel look bad
- What should you do about the problems you find? — which faults are fixable, which are warranty, which you live with
How should you prepare before testing an LCD screen?
Every test below is worthless in the wrong conditions, and the preparation is the same for all of them:
- Clean the panel with a dry microfibre cloth. Dust reads as pixel faults — the safe method avoids the pressure that creates real ones.
- Darken the room. Backlight bleed and contrast problems are invisible in daylight. A dark room is not optional for those two.
- Turn off colour management. Night Light, Night Shift, True Tone, HDR, blue-light filters and any vendor “eco” or dynamic contrast mode.
- Let it warm up. Give the panel fifteen minutes from cold — brightness and colour shift measurably in the first few minutes.
- Set brightness to your normal working level, not maximum. You are testing the screen as you actually use it.
- Run at native resolution, confirmed with our screen resolution test. Scaling hides single-pixel faults and invents softness.
Sit at your normal viewing distance for the first pass of each test, then move closer. Faults that only appear with your nose against the glass are rarely worth acting on.
How do you test an LCD screen for dead pixels?
Start here, because it is unambiguous. Fill the screen with one solid colour at a time and look for anything that does not belong:
- Black — a lit dot is a stuck or hot pixel.
- White — a dark dot is a dead pixel.
- Red, green and blue — a single failed sub-pixel hides on its own colour and shows clearly on the other two.
A dead pixel has lost power and cannot be repaired; a stuck pixel is still powered and often can be. How to run a dead pixel test covers the method in detail, and dead versus stuck pixels covers which one you are looking at.
How do you check for backlight bleed and clouding?
Display a full black screen in a dark room. An LCD blocks the backlight rather than switching it off, so some leakage is normal — you are judging how much.
- Backlight bleed is brighter patches at the edges and corners, where the panel layers do not seal perfectly. Usually worst at the corners.
- Clouding is uneven blotches across the middle of the panel, often from pressure during assembly or mounting.
- IPS glow is a wash of light in the corners that changes as you move your head. This is inherent to IPS panels and not a defect — the movement test is what separates it from real bleed, which stays put.
Photograph it with your phone if you are considering a claim, but be aware that a camera exaggerates bleed dramatically, especially with a long exposure. Judge with your eyes at normal brightness and normal distance. Severe bleed is often covered by warranty; mild bleed almost never is, and no software will change either.
How do you test contrast and black levels?
Contrast is what makes a screen look good or flat, and it is where cheap panels and bad settings show up. Two failures matter:
- Crushed blacks — the darkest shades all merge into the same black, so shadow detail disappears in films and games.
- Blown highlights — the brightest shades merge into white, so bright areas lose all texture.
Our screen contrast test shows a graduated set of dark and light patches. On a well-adjusted panel you should be able to distinguish every step, including the ones very close to black and very close to white.
If steps are missing, adjust brightness and contrast in the monitor’s own menu before concluding the panel is at fault — and turn off any dynamic contrast setting, which alters the image continuously and makes the test meaningless.
How do you check colour uniformity and banding?
Display a mid-grey full screen. It should be the same brightness and the same tint across the whole panel. What you are looking for:
- Brightness falling off toward one edge or corner — uneven backlight, common on large panels and worse as they age.
- Tint shifts, one area warmer or cooler than another — an ageing backlight, since LED output drifts with use.
- Banding — visible steps in what should be a smooth gradient, rather than a continuous transition. This is usually the panel’s bit depth or the graphics output, not a fault.
- Dirty screen effect — a faint mottled texture, most obvious on slow-panning bright scenes like sports.
Also run white and each primary colour full screen. A tint visible on white that is not on grey usually points at a colour-profile problem rather than the panel, which is worth checking in your operating system’s display settings before you blame the hardware.
How do you check resolution, scaling and refresh rate?
A perfectly healthy screen looks soft and wrong if it is being driven incorrectly, and this is a far more common complaint than any panel fault.
An LCD has one fixed grid of physical pixels and only looks sharp when the signal matches it exactly. Anything else is interpolated and blurred. Our screen resolution test confirms whether you are running native, and whether the operating system is scaling on top of that.
Run the screen resolution test
Check the refresh rate at the same time. Running a panel above what the cable can carry causes sparkle, dropouts and artefacts that look convincingly like pixel faults — and a 144 Hz monitor left at 60 Hz is one of the most common setup mistakes there is. How LCD screens work explains why the native grid matters so much.
What should you do about the problems you find?
The results sort into three groups.
Fixable yourself. Stuck pixels, via the flashing method — leave the dead pixel fixer running over the fault for at least an hour. Wrong resolution, scaling and refresh rate, in display settings. Contrast and brightness, in the monitor menu. Colour casts, via the colour profile.
Worth a warranty claim. Dead pixels above the manufacturer’s threshold, severe backlight bleed, obvious clouding, and any cluster of failures — clusters point at impact or liquid damage, which spreads, so act quickly. Photograph everything on both black and white, note positions, and check the policy for your specific model. What to do about a dead pixel covers the claim.
Live with it. Mild bleed, IPS glow, a single dead pixel below threshold, and minor banding. None of these will get worse on their own and none can be repaired.
Whichever it turns out to be, tell us how your test went. We publish the results by manufacturer, and they are what let us say anything useful about which brands ship clean panels.
