Dead Pixel Test
Fill the whole screen with solid white, black, red, green, blue, and gray, one at a time, and look for pixels that don't change.
No permissions. Uses full-screen mode.
Click or press any key to change color. Esc to exit.
Look for pixels that stay the wrong color as the background changes. A pixel that's always black is dead; one stuck on a single color (red, green, or blue on the other backgrounds) is a stuck subpixel; a bright dot on black is a hot pixel. Wipe the screen first -- dust is the most common false positive.
Frequently Asked Questions
What's the difference between a dead pixel and a stuck pixel?
A dead pixel is black on every color -- its subpixels get no power. A stuck pixel is lit on one color (usually red, green, or blue) regardless of the background -- a subpixel stuck on. Stuck pixels sometimes recover; dead ones don't.
I found one. Can I return the monitor?
Manufacturers have pixel-defect policies (often based on ISO 9241-307 classes) that allow a small number of defects before a panel counts as faulty, and retailers add their own return windows. Note how many you found, of which type, and where, and check the policy for your exact model.
Why cycle through several colors?
A stuck red subpixel is invisible on a red background and obvious on black or green. Each solid color exposes a different fault, so the full cycle catches everything a single white screen would miss.
It won't go full screen on my phone.
iOS Safari doesn't allow web pages to enter full-screen mode. The colored overlay still fills the whole browser viewport, so hide the toolbars by scrolling first and test with that.