How this test works
The page sets a CSS background of #ff0000, red at its maximum code value with green and blue at zero, and holds that one color. Look for dark dots and for patches that look blotchy, banded or tinted, then compare the same places on white, green and blue to see which color channel is involved. You do the looking: the page shows the color and does not scan the panel.
Go full-screen red asks for fullscreen through the browser's Fullscreen API. If the browser refuses or has no Fullscreen API, as on iOS Safari, the red field fills the viewport instead and the browser's own controls may stay visible. Leave with ✕, Esc or the browser's fullscreen-exit gesture; the ✕ fades after a few seconds, and a tap on the field or a pointer movement brings it back. The readout shows the color, the hex value, the screen and viewport sizes in CSS pixels as the browser reports them, and whether fullscreen is on, off or an overlay. Everything is read locally in your browser, and nothing is sent anywhere.
#ff0000 is a color value, and color management, your display's settings and the panel itself decide exactly how red it looks and which physical subpixels light. Brightness comes from your backlight or OLED drive level, so set it with the device's controls and keep it low in a dark room.
Frequently asked questions
What is a red screen test used for?
For finding dark dots, patches or uneven color in the panel's red channel. Look over the red field, then compare any spot on white, green and blue: a mark that appears only on red points to a red-channel problem. Outside testing, it works as a red backdrop, or as a dim red work light with the device brightness turned down.
Why test with red instead of just white?
White lights all three color channels at once, so it can show that something is wrong without showing which channel. Compare the same spot on red, green and blue to see where it changes or disappears. This page supplies red, and the white screen page has green and blue swatches.
Why do astronomers and night workers use red screens?
Night vision relies on the eye's rod cells, which are less sensitive to long-wavelength red light, so a dim red screen lets you read a chart while your eyes stay mostly dark-adapted. That is why telescope apps and ship bridges switch to red at night. Brightness still matters: a bright red screen disrupts dark adaptation like any other bright light, so turn the brightness right down.
What does a dark or discolored dot on red mean?
A dot that is dark on red but fine on green and blue points to a red subpixel that is not lighting. A dot that is dark on every color points to the whole pixel, though a mark on the surface can look the same. To check, look for dust on the glass and clean it the way the manufacturer recommends, then step through the dead pixel test's colors and compare the same spot. If the spot stays on a new display, check the manufacturer's pixel policy while you are inside the return window.
Is a static red screen safe for my display?
Yes, for ordinary use. A solid color is normal work for a panel, and this page never flashes or cycles on its own. Just do not leave it running for many hours or overnight, especially on an OLED: long periods of static content can contribute to burn-in on OLEDs, and LCDs can also show image retention. Follow your display manufacturer's guidance for static images.
