About the Red Screen
Filling the display with one primary colour isolates a single sub-pixel channel. On a red field, every lit pixel should be the same saturated red; a dot that appears dark has a failed red element, and a dot that shows green or blue is stuck in the wrong state. Repeating the check across all three primaries is how repair shops decide whether a panel is worth replacing.
Red has a second use that has nothing to do with faults. Human night vision depends on rod cells that are far less sensitive to long wavelengths, so a dim red glow lets you read a star chart or find your way around a tent without losing the dark adaptation that took twenty minutes to build. Set a dark red shade and drop the brightness to around fifteen per cent for that, and photographers use the same trick as a stand in for a darkroom safelight when handling paper.
The deeper shades are also useful for judging how a display handles saturated colour. Cheap panels often crush a strong red into a flat blob with no detail near the edges of the gamut, which is easy to spot when the whole screen shows it. Pair this with the blue screen and the black screen for a full sweep, and use colour blindness simulator if you are checking how a red interface reads for other people.
How to use
- Select a red shade; pure red is best for a sub-pixel check.
- Drop Brightness to about 15 per cent when you want a night safe glow instead.
- Fill the display and look for dots that are dark or the wrong colour.
- Repeat with the blue and white screens so every channel gets tested.
Common questions
- Why does red preserve night vision?
- Rod cells in the eye respond weakly to long wavelength light, so a dim red field lets you see without resetting the dark adaptation your eyes have built up.
- What does a dark dot on a red field mean?
- The red element of that pixel is not lighting. If the same dot stays dark on green and blue fields as well, the whole pixel is dead rather than partly stuck.
- Is a solid red screen good for a chroma key?
- No. Keying works best on green or blue because skin tones contain a lot of red, which would be pulled out along with the background.
- Does the shade affect the test?
- Yes. Only pure red drives the red sub-pixel to full output; the darker shades mix in less light and make faint faults harder to see.