How to Check a Screen for Dead Pixels

Run the test

1. Wipe the screen with a dry microfiber cloth, so dust does not look like a fault.
2. Open Dead Pixel Test and click Start full screen.
3. Look across the whole screen on each color, from about 30 cm away. Click or press Space for the next color, and Esc to finish.

What you might see

• Dead pixel: a black dot that stays black on every color. Easiest to see on white.
• Stuck pixel: a dot that stays red, green or blue. It shows on black and on the other colors.
• Hot pixel: a white dot that stays lit, visible on black.
• Backlight bleed: light leaking in at the edges or corners on a black screen, easiest to see in a dark room.

What to do about it

Test a new screen as soon as it arrives, while you can still return it. Manufacturers have their own policies, often allowing a small number of faulty pixels before they replace a panel, so check the warranty terms and keep a photo of the fault.

Stuck pixels sometimes free themselves after a few days of use. Dead pixels, which get no power at all, almost never come back.

Check the resolution too

When buying second-hand, check the screen resolution as well, to make sure the panel is the one advertised.

Freeing a stuck pixel

A stuck pixel is sometimes freed by making it switch on and off quickly. Show a small box that flashes through bright colors over the pixel for 10 to 20 minutes, then check again. It does not work on dead pixels, and it is not worth pressing on the screen, which can make things worse.

Fast-flashing colors can trigger seizures in people with photosensitive epilepsy. Do not look at the flashing area, and do not use this method if that applies to you.

Other things to check

• Uniformity. On a mid-grey screen, look for darker corners or cloudy patches. Some unevenness is normal on large LCD panels.
• Burn-in on OLED screens. A faint ghost of a status bar or logo that stays on every color is burn-in, not a pixel fault. It is easiest to see on a plain grey or red screen.
• Dust under a laptop screen protector. A dot that moves slightly when you look from another angle is on the surface, not in the panel.

Recording the fault

Photograph the fault with the test color filling the screen, close enough that the dot is clear. Note its position, such as "3 cm from the top, 10 cm from the left", which helps when returning a screen.