Red Screen Test
Light only the red subpixel to isolate a fault white cannot show you.
Only the red subpixel is lit, so a fault in it shows on its own instead of hiding inside white.
Looking at the whole screen, including the corners — what did you see?
How this test works
The page fills the display with pure red, which lights the red subpixel of every pixel and leaves green and blue off. That isolation is the whole point: inside a white field, one failed subpixel is masked by the two that still work, so it reads as a very slight colour cast instead of a fault. On a single-channel fill it reads as a dark speck. The test also reports how much of the panel the fill is actually covering, then interprets what you report — including the distinction between a subpixel fault and a dead pixel, which warranty policies frequently treat differently.
What the results mean
- Dark dot
- The red subpixel at that spot is not being driven. The other two are likely fine, so this is a subpixel fault rather than a dead pixel.
- Even fill
- No visible variation means the red channel is being driven consistently across the panel.
- Blotches
- Uneven red across the field is a uniformity characteristic, most often strongest toward the corners.
Common problems and fixes
- The red looks orange or pink
- That is the panel's colour calibration, not a fault. Wide-gamut displays render pure red noticeably differently from sRGB ones, and OS colour profiles shift it further.
- I found a speck here but not on white
- That is expected and is exactly what this fill is for. One dead subpixel is hidden inside white by the two working ones; only a single-channel fill isolates it.
- My eyes water looking at full red
- Full-saturation red at high brightness is genuinely uncomfortable to stare at. Lower the brightness — the test works just as well dimmer.
Frequently asked questions
Why test red separately from white?
Because white cannot isolate a channel. All three subpixels are lit in white, so a single failed one is masked. A pure red fill is the only condition under which a red subpixel fault appears as an obvious dark speck.
Is a dead red subpixel the same as a dead pixel?
No. A dead pixel is dark on every colour including white. A dead subpixel leaves the other two working, so the pixel still lights — it just renders slightly off-colour. Many warranty policies count them differently.