Black Screen & White Screen Test
Ten exact fullscreen colours for finding dead pixels, backlight bleed and dust, with an auto cycle and arrow-key stepping.
For parody, education, and mockups only
Colour
Walks through black, white, red, green, blue and grey in that order.
4 sec
In fullscreen, the arrow keys or a tap step through the colours. The display is kept awake, and Escape exits at any time.
Everything here runs on your device. Nothing you enter is uploaded or stored.
Ten exact fullscreen colours, each labelled with what it diagnoses. Arrow keys or a tap to step through, or let it cycle. Escape exits immediately.
How to use it
- Pick a colour, or leave it on black.
- Press Start to fill the screen. The display is kept awake while it runs.
- Press the arrow keys, or tap, to step to the next colour.
- Or turn on auto cycle to walk through the six diagnostic colours hands-free.
Every colour here diagnoses something specific
This is the simplest surface on the site and the one with the most genuine utility, so it is worth being exact about what each one is for rather than presenting ten swatches and leaving you to guess.
Black finds stuck subpixels. A pixel that is permanently lit is unmissable against solid black and easy to overlook against anything else. Black is also what you want for cleaning, because dust and smears are nearly invisible against a bright desktop.
White finds dead pixels, which receive no power and stay dark — the opposite case, and invisible on black. White is also the only way to see backlight bleed and IPS clouding, which show as brighter or milkier patches toward the edges.
Red, green and blue each isolate one subpixel. A dead red subpixel appears as a dark speck on the red screen and is invisible on the other two. Green is worth a second look because green carries most of the perceived brightness in an RGB display, so defects show up there first.
Blue specifically is the best background for spotting dust and debris trapped under the glass, which is a different problem from a panel defect and needs a different fix.
Cyan, magenta and yellow test pairs of channels together, which catches a subpixel that is weak rather than fully dead.
18% grey and 50% grey show gradient banding, gamma problems and colour cast — all of which a pure tone hides completely.
Why the cycle is in that order
Black first, then white. The transition between those two is the single most informative moment of the whole test, because it shows backlight uniformity: a panel that looks fine on black and blotchy on white has a bleed problem, and you only see it in the change.
Then red, green, blue in that order, so a missing channel is identifiable by position rather than by remembering which screen you are on. Grey last, because banding is the subtlest thing here and worth looking at with your eyes already adjusted.
The colours are exact, on purpose
A test screen is a measurement surface. If you ask for pure black and the display receives #010101, the test is worthless — you would be looking for a lit pixel against a background that is already slightly lit.
So this is drawn as a flat background colour on a plain element rather than through a canvas. Canvas drawing goes through colour-managed conversion, and the values that arrive at the panel are not guaranteed to be the ones you asked for. Setting a background directly avoids that entirely, and it is the reason this tool is built differently from the other simulators.
Keeping the screen awake
A test pattern that dims after thirty seconds cannot be inspected, and a screen that sleeps mid-clean is worse than useless. The Screen Wake Lock API is requested when the tool starts and released when it stops, where the browser supports it. Where it does not, nothing breaks — you may just need to move the mouse.
What it does not do
It cannot repair a dead pixel. Nothing can, in software: a dead subpixel is a hardware fault. Rapidly cycling colours over a stuck pixel occasionally unsticks it, which is why the cycle option exists, but treat that as a coin flip rather than a fix.
Nothing is uploaded and no permission beyond the wake lock is requested.
Colour reference
| Colour | Value | Finds |
|---|---|---|
| Black | #000000 | Stuck pixels, dust and smears |
| White | #ffffff | Dead pixels, backlight bleed, clouding |
| Red | #ff0000 | A dead or weak red subpixel |
| Green | #00ff00 | Green defects, which show first |
| Blue | #0000ff | Debris under the glass |
| 18% grey | #2e2e2e | Banding and gamma problems |
| 50% grey | #808080 | Colour cast and tint |
Questions
How do I get out of it?
Press Escape. It is bound before the screen appears and works whether the browser granted true fullscreen or fell back to a fixed overlay. The Exit button in the corner does the same if there is no keyboard to hand.
What is the difference between a dead pixel and a stuck one?
A dead pixel receives no power and stays black, so it is invisible on a black screen and obvious on a white one. A stuck pixel is permanently lit in one colour, so it is obvious on black and easy to miss on white. That is why you need both, and why the cycle starts with the two of them in sequence.
Why is this drawn without a canvas?
Because a canvas is subject to colour-managed conversion, and
Can I use this to clean my screen?
Yes, and it is one of the main reasons people want a black screen. Dust and smears are almost invisible against a bright desktop and unmissable against solid black. The screen is kept awake while it runs so it will not dim halfway through.
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