How to use it
- Click the red box above, or press F.
- The whole screen turns red. Move the mouse or press an arrow key to see the controls hint.
- Click anywhere or press Esc to go back.
On an iPhone the browser keeps its address bar, so the color fills the page but not the very top strip. Turn the phone sideways or scroll a little to hide the bar.
What a red screen is for
- Night vision. Astronomers and campers use dim red light because it disturbs eyes that are used to the dark less than white light. Pick dark red and lower the brightness.
- Pixel test. On pure red only the red part of each pixel is lit. A black dot means that part is dead; a bright dot of another color means a stuck pixel.
- Mood and photos. A red screen gives a room or a selfie a strong red cast.
- Alerts and signs. A red screen is easy to see across a room as a "stop" or "busy" sign.
Red light and night vision
For the least disturbance to dark-adapted eyes, use dark red and set brightness low, then turn your device brightness down too. Even red light is too bright at full power in a dark place.
Questions
Is a red screen good for night vision?
Dim red light affects dark-adapted eyes less than white light, which is why astronomers use it. Keep it dim: bright red still dazzles.
Can I use it as a darkroom safelight?
Do not rely on it. A screen is not a tested safelight and may give off light that fogs photo paper.
How do I get out of the red screen?
Click anywhere, tap the screen, or press Esc.