Dead Pixel Test for Monitors and Phones

Faulty pixels show up best against a single colour filling the whole screen. Start the test and the screen goes full screen in one colour; each click, Space or right arrow moves through black, white, red, green, blue, cyan, magenta, yellow and grey. For each colour, scan the screen slowly and up close for any dot that differs from its surroundings.

There are three kinds, told apart by where they show. A dead pixel is stuck off and appears as a black dot on white or any bright colour. A hot pixel (a bright dot) is stuck on and appears as a white dot on black. A stuck pixel has one or two of its red, green and blue subpixels stuck on, so it shows as a coloured dot on black or on another colour. A bright dot on black is far more noticeable than a dark one, and manufacturers' policies usually treat bright dots more strictly.

Wipe the screen with a soft cloth first. Dust and smudges keep their shape when the colour changes and look different from another angle; a faulty pixel appears only on certain colours and sits in exactly the same place. Night mode, HDR and blue-light filters alter the colours, so switch them off, and turn the brightness up. On a phone, full screen may not be available, but the colour still fills the page, so only the edges hidden by the address bar need a separate look.

Check a new monitor straight away, while it can still be returned. How many faulty pixels count as a defect depends on the maker and the seller; look for the pixel fault class under ISO 9241-307 or a zero-bright-dot guarantee. Stuck pixels sometimes free themselves over time, while dead pixels are usually a panel replacement rather than a repair. Tools that flash colours rapidly to unstick a pixel have little evidence behind them and the flashing can trigger photosensitive seizures, so this page does not include one.