One click fills the screen with a flat neutral grey — every subpixel driven equally, none at maximum. It is the field that shows what white washes out: dirty screen effect, mura, faint banding, and any colour cast pulling the panel away from neutral. Also spelled gray. The field is static: it never flashes or cycles on its own.
How this test works
The page holds a single static field of neutral grey — #808080, every channel at the same middling value, so all three subpixels of every pixel are lit and none is saturated. That is what makes grey the uniformity field. White pins every subpixel to maximum, which flattens the small local differences in backlight and liquid-crystal behaviour that produce blotching; at a middling drive level those same differences stay visible. This is the field where dirty screen effect and mura show themselves, where faint vertical or horizontal banding appears, and where a panel that is running warm or green stops looking merely fine and starts looking wrong.
Fullscreen comes from the browser's Fullscreen API, with a full-viewport overlay as the fallback on devices that don't offer it — the ✕ button, Esc, and the browser's own gesture all hand control back, and a tap anywhere re-reveals the ✕ if it has faded. The colour itself is one CSS background the panel renders directly; the page runs no animation and no loop. The readout strip stays live throughout, reporting the hex value, your display resolution as the operating system states it, the viewport size, and the true fullscreen state — all read locally in your browser, with nothing sent anywhere.
The limits are worth stating plainly. This page shows a field; it does not measure one. No browser can read the light actually leaving your screen, so every judgement here — is that blotchy, is that neutral, is that banding — is your eye's, made under whatever room lighting you happen to be in, and a second display in the same room is worth more than any single verdict. Grey is also the wrong field for a single dead subpixel, which needs the primaries lit one at a time. And #808080 is mid-grey by code value rather than by light: sRGB's transfer function puts it at roughly 21.6 percent of white's luminance, not half, which is why it reads darker than the name suggests.
Frequently asked questions
What is a grey screen test used for?
A flat neutral grey is the most revealing background for uniformity faults. Dirty screen effect — the faint blotches, smears and vertical bands that show up when a camera pans across a football pitch — is far easier to see on mid-grey than on white, because white drives every subpixel to maximum and saturates the small differences that make the blotching visible. Grey is also the best field for spotting a colour cast: the eye is unusually good at judging neutrality, so a panel running warm or green announces itself here and hides on almost every other colour.
Is this the same as the dead pixel test?
No, and grey is the wrong field for that job. Finding a dead subpixel means lighting one channel at a time, which is what the red, green and blue fields do — a dot that is dark on red but fine on green and blue is specifically a failed red subpixel. Grey drives all three channels together at a middling level, so a single failed subpixel is muted rather than isolated. Use grey for whole-panel problems like blotching, banding and tint; use the dead pixel test for individual pixels.
Why is #808080 not half as bright as white?
Because sRGB is not linear. The value 128 out of 255 sits halfway along the encoded scale, but the sRGB transfer function maps it to roughly 21.6 percent of the luminance of white, not 50 percent. That is deliberate — the encoding devotes more of its range to darker tones, where human vision is more sensitive to change. So #808080 is the conventional mid-grey by code value and looks like a fairly dark grey by light output, and both of those statements are correct at once.
My grey screen looks pink, green or blue — what does that mean?
It means the display is not neutral at that level, which is the single most common thing a grey field reveals. Ordinary causes are a colour profile or a night-light or blue-light filter still running, a monitor preset such as warm or cinema mode, or an ageing backlight. Turn off any night-shift mode and try again before concluding anything about the hardware. This page cannot measure the cast: no browser can read the light actually leaving your screen, so the judgement is your eye's, and comparing against a second display in the same room is the practical check.
Is a static grey screen safe for my display?
Yes. A solid colour is ordinary work for a panel, and this page never flashes or cycles on its own — the field changes only when you change it. Grey is in fact the gentlest of the test fields, since it drives every subpixel well below maximum. The usual static-image caution still applies on OLED, where many hours of an identical picture contribute to burn-in, so do not leave it parked overnight. LCDs are effectively immune.
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