Uses for a red screen
- A dim night light that protects night vision. Red light disturbs your dark-adapted eyes far less than white, which is why astronomers, pilots and photographers in darkrooms use it. Turn the brightness down and use your phone as a red torch.
- Testing the red sub-pixels. Every pixel is made of red, green and blue parts. On a pure red screen, a pixel with a faulty red part shows as a black dot.
- Photography and video. A tablet showing red makes a cheap coloured fill or background light for product shots and moody portraits.
- Parties and signals. Hold up a phone showing red as a simple stop sign or a coloured glow.
How to use it
Press Start red screen or click the preview. Use the brightness slider (or the up and down arrow keys) to make it dimmer. While it is full screen, the left and right arrow keys switch between colours, and you can pick any shade with the colour picker before you start. Press Esc or double-click to exit.
For a proper pixel check, the dead pixel test steps through red, green, blue, white, black and grey, so faults in any part of a pixel show up.
Red light and night vision
Your eyes take around 20 to 30 minutes to fully adjust to the dark, and a burst of bright white light resets that in a moment. The rod cells that do most of the work in the dark are much less sensitive to deep red, which is why a dim red light lets you read a map, find your way or check a star chart without losing your night vision. For the best effect, turn your phone's own brightness right down as well as the slider here, and hold the screen low and away from your eyes. A red screen also makes a gentle glow for a child's room or a late-night feed, as it is far less dazzling than white at the same brightness.