Red Screen
A plain red screen. Go full screen, then press Esc to come back.
Look over the whole screen for dots that stay a different color.
Use your monitor or phone controls to raise the brightness. To come back, press Esc or click Exit full screen.
Ready.
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How to use this test
A full-screen red page for checking the red channel of a display and finding stuck pixels. Pixels that stay dark on red but light up on other colors have a failed red sub-pixel.
Press Go full screen and look across the whole display. Compare with the green and blue pages to narrow down which sub-pixel has failed. Press Esc or click Exit full screen to return.
What the results mean
The red should be flat and even. A dark dot that disappears on green or blue is a dead red sub-pixel. Red is also the color on which uneven tint across the panel is easiest to see.
Common questions
Why test red separately?
Each pixel has red, green and blue sub-pixels that can fail independently. A single-color screen shows which one is broken.
The red looks orange on my screen.
That's the display's color calibration or a night-light mode, not a fault. Turn off blue-light filters before judging color.
Can I use this page as a red light?
Yes. At low brightness it's a gentle light that doesn't disturb night vision as much as white.