One click fills the screen with pure red — only the red subpixels lit, green and blue off. Use it to catch stuck subpixels and uniformity problems the white screen hides, or turn the brightness down and use it as a low-glare red light for dark rooms. The field is static: it never flashes or cycles on its own.
How this test works
The page holds a single static field of pure red — #ff0000, the red subpixel of every pixel at maximum while green and blue stay off. That isolation is what a red screen is for: white tells you a pixel is wrong, red tells you which channel. A sharp dark dot that appears only here is a failed red subpixel; blotches, banding, or a visible tint gradient point at uniformity problems in the panel or its driving electronics. The same field, dimmed, is a practical work light — red is the traditional choice where preserving dark adaptation matters, from telescope charts to ship bridges.
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 color 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 knowing. Without hardware calibration, #ff0000 is whatever your panel's red primary happens to be — a wide-gamut monitor shows a deeper red than an sRGB one, and no browser can measure the wavelength it emits, so treat the night-vision use as practical rather than precise. Brightness is hardware too: the page drives the red channel to its maximum value, but the light output depends on your backlight or OLED drive level, which only you can change. And as with any static image, avoid parking it on an OLED for many hours.
Frequently asked questions
What is a red screen test used for?
A pure red field drives only the red subpixel of every pixel and turns the other two off. That isolation is the point: a dark dot on red means a failed red subpixel, and a red field that looks blotchy or uneven can reveal tint and uniformity problems that white hides. Outside testing, people use it as low-glare mood lighting and as a dim red work light for dark rooms.
Why test with red instead of just white?
White lights all three subpixels at once, so it tells you that something is wrong but not what. Red, green, and blue fields each light exactly one subpixel per pixel, which lets you name the culprit: a dot that's dark on red but fine on green and blue is specifically a dead red subpixel. This page covers red — the white screen's swatches cover green and blue.
Why do astronomers and night workers use red screens?
Night vision relies on the eye's rod cells, which are least sensitive to long-wavelength light — so a deep red display lets you read a chart while your dark adaptation mostly survives. That's why telescope apps and ship bridges run red at night, and a red screen at low brightness is the browser version of the same idea. The key variable is still brightness: a dazzling red screen costs you your night vision like any other bright light.
I see a dark or discolored dot on the red screen — what does it mean?
A sharp dark dot that only appears on red is a red subpixel that has failed or is stuck off; if the same dot is dark on every color, the whole pixel is dead. First wipe the screen — dust produces most false alarms — then confirm on the full dead pixel test, which cycles all the primaries and tells you which subpixel is at fault. If it's a real defect on a new display, check the manufacturer's pixel policy while you're inside the return window.
Is a static red screen safe for my display?
Yes. A solid color is ordinary work for a panel, and this page never flashes or cycles on its own — the color changes only when you change it. The one caution is the same as for any static image: on OLED screens, many hours of the identical picture contribute to burn-in, so don't leave the red field parked overnight. LCDs are effectively immune.