Red Screen

How to use the red screen

1. Press Open full red screen. The whole screen turns red and the mouse pointer hides after a moment.
2. For a pixel check, use Pure red at full brightness. For a night light, pick Night red or Maroon and turn the brightness down.
3. Set Auto close if you leave the screen on as a light, so it switches off on its own.
4. Press Esc, or tap the screen on a phone, to come back to this page.

What the results mean

Pure red (#FF0000) lights only the red subpixel in every pixel. The green and blue subpixels are off, so a red screen tests one channel on its own. A healthy panel shows one even red from corner to corner. Look for:

• A black dot: the red subpixel there is dead or stuck off. If the same spot is also black on the white screen, the whole pixel is dead.
• A green, blue or white dot: a green or blue subpixel is stuck on. The stuck pixel fixer can sometimes revive it.
• Darker or orange-looking areas: uneven backlight or a colour shift across the panel. Some fall-off at the edges is normal on LCDs.

For a full check of all three colour channels in one go, run the dead pixel test, which steps through red, green, blue and more.

What a red screen is used for

Night vision light. Your eyes adapt to the dark mostly through rod cells, which are barely sensitive to deep red light. A dim red screen lets you read a star chart, find your way or check on a sleeping child without losing your dark adaptation. Astronomers and sailors use red light for exactly this. Pick Night red and set the brightness as low as it goes.

Pixel and colour checks. Because a red screen uses one subpixel only, it shows faults that a white screen can hide, such as a single dead red subpixel or a tint in one corner. Repeat on the green and blue screens to cover all three channels.

Mood light and signals. A red tablet or monitor makes a quick party or photo light, a "recording" or "do not disturb" sign outside a door, or a stop signal in a game.

Evening use. Red light has less effect on your body clock than white or blue light at the same brightness, so a dim red screen is a gentler choice late at night than a bright white one.

Common problems and fixes

The red looks orange or pink

Turn off night mode, Night Shift or blue light filters, and set the monitor to its standard or sRGB picture mode. Vivid modes and a wrong colour profile push pure red towards orange or pink.

The red is too bright to use as a night light

Choose Night red (25%) and lower the screen brightness to the minimum. On a phone, also turn on the accessibility "reduce white point" or extra dim option for an even darker red.

Full screen does not work on my iPhone

iPhone Safari does not let websites go fully full screen, so the red fills the browser window instead. Rotate to landscape or add the page to your home screen for the cleanest view.