Dead Pixel Test

Clean the screen first. A speck of dust looks exactly like a dead pixel. Wipe the panel with a soft cloth and dim the room lights if you can.

Start the full-screen test. The page fills with solid white, then black, red, green, blue and grey. Click, tap or press the right arrow to move on, the left arrow to go back and Esc to leave.

Look corner to corner on each colour. A dead pixel shows as a black dot on the bright colours. A stuck pixel shows as a dot of the wrong colour, such as a red dot on the green screen. A bright pixel shows as a white dot on black.

Try the flasher on a stuck pixel. It rapidly cycles colours in a small square that follows your pointer, so you can park it over the pixel for a few minutes. Some stuck sub-pixels free up with this. Dead pixels never do.

Dead pixel. The sub-pixels no longer switch on, so it stays black on every colour. It cannot be revived, and manufacturers only replace panels above their own threshold of dead pixels, which varies by brand.

Stuck pixel. One or two sub-pixels are held on, so it shows red, green, blue or a mix. The flasher frees a share of these. Gentle pressure through a soft cloth sometimes helps, but do not press hard on a laptop panel.

Bright or hot pixel. All sub-pixels stuck on, showing white on the black screen. Treat it like a stuck pixel and try the flasher.

Lines, clusters or patches. A column or row of dead pixels, or a growing dark patch, is a panel or ribbon fault rather than a single pixel. The grey screen also shows backlight bleed along the edges and uneven brightness across the panel.