What the dead pixel test shows
Each pixel is three subpixels — red, green and blue — and a fault can affect one or all of them. Filling the screen with each primary in turn isolates them: a subpixel that never lights shows as a dark speck on that colour and nowhere else, which tells you exactly what has failed.
Black and white matter most. On white, a dead pixel is an obvious black dot. On black, a stuck pixel is a bright one that should not be there. Both are far easier to see at full screen than in a window, because there is nothing else on the display to look at.
How to run a dead pixel test properly
Clean the screen first. The overwhelming majority of "dead pixels" people find turn out to be dust, and a microfibre cloth settles it in seconds. Then dim the room: a reflection off a bright window will hide a fault completely.
Work through the colours with a click or the arrow keys, and look at the whole panel rather than scanning it in strips — a fault is far easier to catch in peripheral vision than by staring directly at each region.
- Dead pixel — black on every colour, including white. The subpixels get no power.
- Stuck pixel — bright red, green or blue, most visible on black. Sometimes recoverable.
- Hot pixel — always white. Rare, and normally permanent.
- Dust — moves or disappears when you clean the screen. By far the most common.
What this test cannot tell you
This shows you a colour. It cannot inspect your panel, count faults for you, or tell you whether a fault is within your manufacturer’s warranty threshold — most allow several dead subpixels before they will replace a display.