WS
Site Language:

Screen test

Click the screen, or use the arrow keys or spacebar, to step through the colours. Press Escape to leave fullscreen.

White screen
Black Screen
Red Screen
Green Screen
Blue Screen

What a full-screen test reveals about your display:

  • Dead pixels: permanently black dots

    A dead pixel receives no power, so it stays black on every colour in the sequence. The white and light-grey steps expose it fastest, because a black dot on white is the highest-contrast pairing your eye can be given. If a dot is black on white, red, green and blue alike, the sub-pixels are not switching at all and no software fix will bring it back — it is a hardware fault, and on a new panel it is the strongest evidence you have for a warranty claim.

  • Stuck pixels: one sub-pixel jammed on

    A stuck pixel is the opposite failure: a sub-pixel is locked in the on state, so it glows red, green or blue instead of going dark. The black step is where these announce themselves. Stuck pixels are worth finding because, unlike dead ones, they sometimes recover — rapidly cycling colours over the affected area can un-jam the liquid crystal, which is exactly what stepping quickly through this test does.

  • Telling the two apart before you claim a warranty

    Manufacturers apply pixel-fault thresholds — often a minimum number of dead sub-pixels before a panel qualifies for replacement — and the distinction matters when you file. Run the full sequence and note, per fault, which steps it appears on. A dot visible on every step is dead; a dot visible only on black is stuck; a dot that changes colour between steps is a partially failed sub-pixel cluster. Photograph the screen on the step where the fault shows most clearly.

  • Backlight bleed around the edges

    The black step, viewed in a dark room, shows where light from the backlight escapes past the panel edge. Bleed looks like bright patches or streaks intruding from the bezel, usually at corners. A little is normal on edge-lit LCDs; large uneven blooms are a defect. Judge it only on a genuinely black full-screen image with the room lights off — a black desktop wallpaper cannot show you this, because the taskbar and window chrome keep pushing light into the panel.

  • IPS glow versus clouding

    On the black step, IPS panels show a silvery sheen that shifts as you move your head — that is IPS glow, an inherent characteristic of the technology, not a fault. Clouding is different: irregular lighter patches that stay put no matter your viewing angle. The test tells them apart because you can hold one solid black frame and move while the image stays constant. Glow moves with you; clouding does not.

  • Brightness uniformity across the panel

    The mid-grey step is the most revealing frame in the whole sequence. Solid grey makes uneven backlighting obvious in a way that white cannot, because white saturates your perception and hides gradual falloff. Look for the centre reading brighter than the corners, or one edge darker than the other. Uniformity problems matter for photo and video work, where you will otherwise correct an image to compensate for your monitor rather than for the file.

  • Colour-channel faults on red, green and blue

    The pure primary steps drive a single sub-pixel type at full output. If the red frame shows dark specks that the green and blue frames do not, you have located failures confined to the red sub-pixels. This is also how you catch a failing panel connection: a whole column or row dropping out on one primary but not the others points at the ribbon cable or driver rather than at individual pixels.

  • Banding and gradient smoothness

    Stepping between the grey and colour frames shows whether your display renders tonal transitions cleanly. Visible steps or bands rather than a smooth change usually indicate a 6-bit panel using dithering to simulate 8-bit colour, or a bit-depth mismatch in your GPU output settings. Worth checking before you blame an image file for banding that your monitor is introducing.

  • Finding dust and smears you cannot otherwise see

    Dust is nearly invisible against a busy desktop and obvious against a solid field. The white and black steps together catch almost everything: dark specks and fibres show on white, while greasy smears and fingerprints — which scatter light rather than block it — show on black. Clean between the two steps and re-check, rather than cleaning once and assuming you got it.

  • Checking a screen before you buy it

    If you are buying a used monitor, laptop or phone, running this test takes under a minute and is the single most useful check available to you. Load the page on the device, step through the full sequence, and watch the black and white frames in particular. Sellers rarely disclose pixel faults or backlight bleed, and both are effectively impossible to spot on a normal desktop image.

  • Verifying a repair or panel replacement

    After a screen replacement, the same sequence gives you a like-for-like comparison against the fault you documented before the repair. Run it immediately, while you still have recourse. Refurbished panels are sometimes swapped for units with their own minor defects, and a test run at the counter is far easier than a second warranty conversation a fortnight later.

  • Testing projectors and TVs, not just monitors

    Cast or connect this page to a television or projector and the same frames answer different questions. On a projector, the white step shows lamp uniformity and any dust inside the light path; on an OLED television, the mid-grey step is the standard way to reveal uneven wear or early burn-in from static logos. Full-screen solid colour is the diagnostic tool in every one of these cases.

Frequently Asked Questions

How do I run the screen test?

Press the fullscreen button, then click anywhere or use the arrow keys or spacebar to move through the colour sequence. Each step fills the entire display with one solid colour so nothing competes for your attention. Press Escape to leave fullscreen at any point. The test runs entirely in your browser, needs no download or sign-up, and works on phones, tablets, laptops, monitors, projectors and televisions.

What is the difference between a dead pixel and a stuck pixel?

A dead pixel gets no power and stays black on every colour, including the white step. A stuck pixel has a sub-pixel locked in the on position, so it shows as a bright red, green or blue dot and is most visible on the black step. The practical difference is that stuck pixels sometimes recover on their own or after rapid colour cycling, while dead pixels are a permanent hardware fault.

Can this test fix a stuck pixel?

Sometimes. Rapidly cycling colours over a stuck sub-pixel can unstick the liquid crystal, and stepping quickly through the sequence for several minutes is a reasonable thing to try. It is not guaranteed and it will do nothing for a genuinely dead pixel. Avoid the widely repeated advice to press hard on the panel — the risk of creating a permanent pressure mark or spreading the damage outweighs the small chance of success.

Why not just use a solid-colour desktop wallpaper?

Because the taskbar, dock, icons, cursor and window borders all stay on screen, and every one of them puts light into the panel. That matters most for the black step, where backlight bleed and clouding are judged, and where any bright element on screen destroys your dark adaptation. A true fullscreen frame with nothing else drawn is the only way to see these faults properly.

How many dead pixels before a warranty replacement?

It depends entirely on the manufacturer and the product tier, and the thresholds are set out in the warranty terms rather than by any universal standard. Some accept a single bright sub-pixel on premium panels; others require several faults, or faults within the central zone of the screen. Document what you find with photographs of the specific test step where each fault is clearest, then check your warranty document for its stated pixel policy.

Is it safe to run on an OLED screen?

Yes for a short diagnostic run. Stepping through the sequence for a minute or two poses no meaningful risk. What you should avoid on OLED is leaving any single static bright frame — particularly the white step — on screen for a long period, since prolonged static content is what drives uneven wear. Keep the test brief, keep stepping, and do not leave it running unattended.

Does it work on a phone or tablet?

Yes. Tap to advance through the steps instead of using the keyboard. Mobile screens are worth testing for exactly the same faults, and the black step is especially useful on a phone you are buying second-hand, since it shows both stuck pixels and any pressure damage or discolouration behind the glass that a busy home screen hides.

What is IPS glow and should I worry about it?

IPS glow is a silvery brightening visible in the corners of an IPS panel on dark content, and it shifts position as you change viewing angle. It is inherent to the panel technology and is not a defect. Clouding, by contrast, is irregular blotchy lightness that stays fixed regardless of where you sit. Hold the black step and move your head — if the pattern moves with you it is glow, and if it stays put it may be worth raising.

Why does the test include a grey step?

Mid-grey is the most sensitive frame for judging backlight uniformity. Pure white overwhelms your perception and masks gradual brightness falloff toward the edges, while black shows only leakage. A uniform grey field sits in between and makes centre-to-corner variation, blotches and dirty-screen effect visible — which is why grey slides are standard in professional display calibration.