Skip to content

Which store is yours? We'll remember it and show you the right details.

Ed's PCs
Support

Tech Zone

Screen Test

Fill the whole screen with one colour at a time and look at it properly. It's the fastest way to find a dead pixel, a stuck one, or light leaking in from the edge of the panel — and it takes about a minute.

Clean the screen first. Most "dead pixels" people bring in are dust.

Pick a pattern to start

It goes full screen. Click or tap to move to the next pattern, arrow keys work too, and Esc gets you out at any time. On anything that moves, the scroll wheel changes the speed.

What each one finds

Red
A sub-pixel that never lights: the dot stays black on red.
Green
The same again — green is the channel your eye is most sensitive to.
Blue
Blue shows dust and smears as well as dead dots.
White
Dead pixels (black dots), dust, and yellowing at the edges.
Black
Stuck pixels (bright dots), backlight bleed and clouding at the corners.
Grey ramp
Banding, an uneven backlight, and whether dark greys separate at all.
Grid
Geometry and scaling — the lines should be even and perfectly straight.
Moving band
Runs colours over every pixel. Click again for the same band going down instead of across. Leave it going to try to free a stuck one.
Moving bars
The whole colour set sweeping at once — across, then down on the next click. Faster coverage, and it shows up tearing and judder.
Test card
The old TV pattern: geometry, convergence, colour and greyscale in one picture.
Display info
What your screen actually is — resolution, real pixels, refresh rate, colour depth and gamut.
Bouncing logo
A moving object on black. Good for judder and ghosting, and it's the old DVD screensaver.

Reading the result

  • A black dot on every colour is a dead pixel — the whole pixel has stopped. Nothing frees those; it's a panel replacement or living with it.
  • A dot that's bright red, green or blue on a black screen is a stuck sub-pixel. Leave the moving band running on it for ten or fifteen minutes — a fair few of them come good.
  • Glow creeping in from the corners or edges on the black screen is backlight bleed. A little is normal on every LCD ever made; a lot, or a bright patch, is a fault.
  • A cloudy patch that moves when you press the bezel is pressure damage to the panel. Stop pressing it.
  • A coloured cast or a line down the screen is usually the cable or the connection, not the panel — worth checking before anyone quotes you for glass.

This is a test, not a diagnosis. A laptop screen with a real fault is one of the jobs we do most —see what's usually on the shelf before you drive in.