Dead Pixel Test
Fill the screen with one color at a time and look for dots that don't change.
Look over the whole screen for dots that stay a different color.
Use your monitor or phone controls to raise the brightness. To come back, press Esc or click Exit full screen.
Ready.
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How to use this test
The dead pixel test fills the screen with white, black, red, green and blue in turn. A pixel that stays dark on every color is dead; one that stays lit in a single color is stuck. It works on monitors, laptops, phones, tablets and TVs used as displays.
Press Go full screen, then click or use the arrow keys to move through the colors. Look over the whole screen at each color, including the edges, from a normal viewing distance and then closer. Press Esc or click Exit full screen. Wipe the screen first so dust isn't mistaken for a pixel.
What the results mean
A spot that is black on white and every other color is a dead pixel. A spot that shows red, green or blue on the black screen is a stuck sub-pixel; these sometimes recover. A patch that looks slightly brighter or darker on a solid color is a uniformity issue rather than a pixel fault. Most manufacturers only replace a panel above a certain number of defects, so count them.
Common questions
Can a stuck pixel be fixed?
Sometimes. Leaving a rapidly changing pattern on the spot for a while, or very gentle pressure through a soft cloth, occasionally frees a stuck sub-pixel. A dead pixel that is black on all colors won't recover.
How many dead pixels are acceptable?
It depends on the manufacturer's policy and the panel class. Several allow a few defects before a warranty replacement, so check the policy for your model before claiming.
I see a faint gray patch on the white screen.
That's backlight or panel uniformity, not a dead pixel. The Screen Test has a dedicated uniformity chart for judging it.