Dead Pixel Test

How to test your screen for dead pixels

1. Wipe the screen with a dry microfibre cloth. A speck of dust looks exactly like a dead pixel.
2. Press Start full-screen test, or click one of the swatches next to or start at: to begin with a specific colour.
3. The browser switches to full screen and shows a single solid colour. Click or tap to go to the next colour, click the left third of the screen (or right-click) to go back. The arrow keys, Space and Page Up/Down also work.
4. Scan the whole screen slowly, section by section, from a normal viewing distance. Then look closer at anything suspicious.
5. Press Esc or the ✕ Exit button to leave. The hint and the button fade after a few seconds, and the mouse pointer hides when you stop moving it so it never covers a pixel. Press H to bring the help back.

The sequence is black, white, red, green, blue, cyan, magenta, yellow and a 50 % grey. Nine colours are enough to reveal every common pixel fault.

Dead, stuck and hot pixels

Each pixel on an LCD or OLED screen is made of red, green and blue sub-pixels. A fault in one of them shows up differently depending on the colour on screen:

• Dead pixel: always dark. It is most visible on the White screen and on bright colours. On an LCD it usually means the transistor that drives the pixel has failed.
• Stuck pixel: always shows one colour, such as a bright red or green dot. It stands out on Black and on colours that don’t contain that primary. A pixel stuck on red is invisible on red, yellow and magenta but obvious on blue or cyan.
• Hot pixel: always lit white. It is easiest to see on Black.
• Partial sub-pixel fault: the pixel looks wrong on only one or two colours. Cycling through all the swatches is how you catch these.

On OLED screens, check the Grey 50 % screen too: it helps reveal burn-in and uneven wear that solid primaries can hide. For backlight bleed, clouding and banding, use a uniformity test with grey levels and gradients instead.

The stuck pixel fixer

The optional Stuck pixel fixer (optional) section shows a small square that cycles red, green, blue, white and black. The idea is to exercise the stuck sub-pixel until it responds again. It sometimes helps a stuck pixel that appeared recently; it rarely helps a dead (black) pixel, and nothing is guaranteed.

Because it changes colour repeatedly, it is off by default. It only starts after you tick I have read the warning and want to use the flashing square. The speed is capped at 3 changes per second (maximum), the square is at most 128 CSS pixels wide, and it stops by itself after the time chosen in Stop after. These limits keep it within the WCAG guidance on flashing content (no more than three flashes per second), and if your device asks for reduced motion the speed is limited to one change per second. Drag the square over the stuck pixel, look away, and press Esc or Stop at any time. Many dedicated fixer tools flash much faster; this tool deliberately doesn’t.

When to worry

Most panel makers have a pixel policy: a few bright or dark pixels may be considered within specification, especially outside the centre of the screen. Test a new monitor, laptop or phone as soon as you receive it, while you can still return it, and take a photo of any fault on a solid background.