Dead, hot, and stuck: three different defects with one name
"Dead pixel" gets used loosely, but a panel can fail in a few distinct ways. A dark dot defect (a dead or dark pixel) is a pixel stuck fully off: the backlight is there, but no light reaches through at that spot, so it shows as a black dot against any bright background. A bright dot defect (a hot pixel) is the opposite: a sub-pixel stuck fully on, showing as a colored or white dot against a dark background regardless of what the rest of the screen displays.
A stuck sub-pixel is narrower still. Each pixel is built from three sub-pixels, red, green, and blue, and a stuck sub-pixel is just one of those three frozen on or off while the other two keep working. That's why the red, green, and blue full-screen tests exist separately: a stuck red sub-pixel is invisible on a pure-red screen (everything is red anyway) but stands out clearly on a pure green or blue one.
How the two modes in this tool work
The solid-color test cycles through six full-screen colors, black, white, red, green, blue, and 50% gray, and you click or use the arrow keys to step through them while scanning for a dot that stays put. Gray sits between black and white and often reveals uneven backlighting or clouding that pure black or white can hide.
The pixel-refresh mode instead flashes through those colors rapidly (8 times per second here) for a duration you pick. Rapid color cycling like this is a documented approach some users report success with for a stuck sub-pixel specifically, on the theory that the rapid switching can jar loose the liquid crystal material behind a sub-pixel that is stuck rather than physically dead. It has no effect on a dead or hot pixel, since those come from a failed transistor rather than a temporarily stuck crystal, and even on a stuck sub-pixel it isn't guaranteed to work.
The ISO 13406-2 class system, and why "ISO-approved" doesn't mean flawless
ISO 13406-2 was the ergonomics standard that first defined pixel fault classes for flat-panel displays, from Class I (zero defects tolerated) down to Class IV (up to 50 hot pixels, 150 dead pixels, and 500 stuck sub-pixels allowed per million pixels). Most manufacturers built their displays to Class II, the second-strictest tier. The standard itself was withdrawn in the 2000s and formally revised by the ISO 9241-302/303/305/307:2008 series, but the old Class II numbers are still the figures most commonly quoted in manufacturer support pages and consumer pixel-policy discussions today.
ISO 13406-2 sets fault classes for display defects. Wikipedia's article says most manufacturers specify Class II, but the citation attached to that claim is flagged as failed verification (checked 13 October 2026). To know whether a panel qualifies for a return, check the manufacturer's current warranty page.
Worked example: what "allowed" looks like on a real screen
Class II allows 2 hot pixels and 2 dead pixels per million pixels. A 1920×1080 monitor has 1,920 × 1,080 = 2,073,600 pixels, so the allowance scales to 2 × 2,073,600 ÷ 1,000,000 = 4.15, rounded down to 4 hot pixels and 4 dead pixels before the panel would fall outside Class II. The stuck-sub-pixel allowance is looser, 5 per million, which works out to 5 × 2,073,600 ÷ 1,000,000 = 10.37, rounded down to 10 on the same panel. Move up to a 3840×2160 (4K) panel with 8,294,400 pixels and the same 2-per-million hot/dead allowance scales to 16, since a 4K panel simply has four times as many pixels for defects to be spread across.
Before you assume it's a defect
Wipe the screen with a dry microfiber cloth first. A speck of dust or a smudge can look identical to a dead pixel from a normal viewing distance, and it disappears with a wipe while a pixel defect does not. If it survives a cleaning and shows up in the same screen location across every color in the test, at every viewing angle, it is a pixel-level defect, not something sitting on the glass.