Dead pixel test
Fill the screen with one colour at a time and look for a dot that does not match. Works on a monitor, laptop, TV, phone or tablet.
Next: →, Space, click, tap or swipe left. Back: ← or swipe right. Leave: Esc.
This browser cannot put a web page in full screen (iPhone Safari cannot; iPad Safari can from iPadOS 16.4). The test fills the browser window instead, and Safari's bars stay. To cover more of the screen:
- Tap Share, then Add to Home Screen, and open the page from that icon: it opens without Safari's address bar. The status bar with the clock stays.
- Or, in Safari, open the page menu at the left of the address bar (aA on many iOS versions) and choose Hide Toolbar.
- Turn the brightness up and lock rotation if the screen keeps turning.
Stuck-pixel helper
Found a dot stuck on red, green, blue or white? Drag a small flashing square over it and leave it for 10–20 minutes. It sometimes frees a stuck (coloured) pixel and cannot revive a dead (black) one.
The helper is off because your device asks for reduced motion. It flashes colours many times a second, which is exactly what that setting asks pages not to do. The still colour screens work as normal. If you want the helper anyway, switch off Reduce motion (iPhone: Settings, Accessibility, Motion; Windows: Settings, Accessibility, Visual effects, Animation effects; Mac: System Settings, Accessibility, Display) and reload.
Warning: flashing colours
The helper flashes a square through red, green, blue, white and black up to 60 times a second. Do not use it if you, or anyone who can see the screen, has photosensitive epilepsy or has ever had a seizure from flashing lights. You do not need to watch it: start it, then look away or leave the room.
How to check a screen for dead pixels
- Wipe the screen with a dry microfibre cloth. Dust looks exactly like a dead pixel on white.
- Turn the brightness up and press Start full-screen test. The screen turns black and the pointer disappears.
- Step through black, white, red, green, blue and grey with →, a click or a tap. On each, scan the whole screen in strips from about 30 cm away; a magnifying glass or your phone camera's zoom helps on a 4K panel.
- If you see a dot, step to the other colours and note which ones it shows on (see the table below). Photograph it if you plan to return the screen.
- Carry on to the backlight bleed screen in a dark room, the grey ramp and the 1-px grid, then press Esc to leave.
What a dot on each colour means
| What you see | It is | Best screen to spot it |
|---|---|---|
| Black on every colour | Dead pixel | White |
| Black on red only (or green, or blue) | Dead subpixel: one of its three colour cells is off | That colour |
| Red, green or blue on black | Stuck pixel (one subpixel always on) | Black |
| White on black | Hot pixel (all three always on) | Black |
| Same grey spot on every colour, moves when you wipe | Dust or a smudge on the glass | White |
Worked example: a laptop shows a tiny green dot on the black screen. On the red screen it shows as a yellow dot (red plus green) and on blue as a cyan one; on green it vanishes, and on white it is barely visible. That is a stuck green subpixel, the kind the helper sometimes frees. Had it been black on white, red, green and blue, it would be dead and the helper would not help.
Backlight bleed, IPS glow and uniformity
An LCD lights every pixel from behind. Where the panel's frame presses unevenly, that light leaks round the edges as bright patches, usually in the corners: backlight bleed. Check it in a dark room with brightness at maximum, looking straight at the centre from your normal distance; a camera exaggerates it, so judge by eye. IPS glow is a different, normal effect: a faint silvery or yellow sheen in the corners of IPS panels that moves or changes when you move your head. Bleed stays put. OLED screens have no backlight, so they have no bleed; their black screen should be completely dark.
The grey ramp shows 16 flat bands from black to white. Each band should be an even tone from top to bottom; a darker blotch or vertical stripe running across bands is a uniformity fault, sometimes called dirty screen effect on large TVs. If the first two or three bands look the same black, the screen (or its contrast or black-level setting) is crushing shadows.
The 1-px grid
The grid draws white lines one device pixel wide every 8 pixels, with the outermost row and column of pixels in red. At the screen's native resolution and 100% scaling every line is crisp. Blurred, doubled or wavy lines mean the picture is being scaled: set the computer to the panel's native resolution. A TV that cuts off one or more red edges is overscanning; turn on its "Just scan", "Screen fit" or "1:1" picture-size option.
What it cannot do
- It cannot repair a screen. The helper sometimes frees a stuck pixel; it cannot revive a dead one, a pressure mark or a cracked panel.
- It cannot find a pixel for you: a web page cannot read what your screen shows, so a fault is only found by looking.
- On iPhone it cannot hide Safari's bars or the status bar, because iPhone Safari gives pages no full-screen mode; the edges they cover are not tested unless you use the steps above.
- It shows the colours your system sends. Night Shift, Night Light, True Tone, a blue-light filter or an HDR mode tint them; switch those off for a fair test.
- It cannot test a screen the browser is not showing: on a second monitor, drag the window there before you press Start.
Privacy
Nothing leaves your device and nothing is saved. The page sends an anonymous page-view count and one of two fixed words, screen-test-start and stuck-helper-start.
Questions
How do I test a monitor for dead pixels?
Clean the screen first, then press Start. The page goes full screen on black; press the right arrow key, click or tap to step through white, red, green, blue and grey. On each colour, look across the whole screen from about 30 cm for a dot that does not match. A dot that stays black on white is dead; a dot that stays lit or coloured on black is stuck. Press Esc to leave.
How do I do a dead pixel test on an iPhone?
Tap Start: on iPhone the colours fill the Safari window, because iPhone Safari does not let a web page go full screen (iPad Safari does, from iPadOS 16.4). To cover the toolbars too, add the page to your Home Screen with Share, Add to Home Screen, and start it from that icon, or hide Safari's toolbar from the page menu in the address bar. Tap to step through the colours and tap Leave to stop. The status bar at the very top stays.
How do I test an Android phone screen for dead pixels?
Open the page in Chrome, Samsung Internet or Firefox and tap Start. The page goes full screen and hides the status and navigation bars. Tap the middle of the screen or swipe left to go to the next colour; a swipe from the very edge may be taken by Android's back gesture. Tap the screen and then Leave, or use the back gesture, to stop.
Can this fix a dead or stuck pixel?
It cannot repair anything. The stuck-pixel helper flashes a small square through red, green, blue, white and black that you drag over a stuck pixel, one that stays red, green, blue or white, and leave running for 10 to 20 minutes. That sometimes frees a stuck pixel. It cannot revive a dead pixel, one that stays black on every colour. The helper starts only after you accept a photosensitive-seizure warning.
What is the difference between a dead pixel and a stuck pixel?
A dead pixel stays black whatever the screen shows, so it is easiest to see on the white screen. A stuck pixel stays one colour, usually red, green or blue, so it is easiest to see on black; on the screen of its own colour it vanishes. A hot pixel is a stuck pixel that stays white. If the spot stays the same on every colour and moves when you wipe the glass, it is dust.