Whether you've just unboxed a new display, picked up a used monitor, or you're chasing a mark that only shows on certain colours, it pays to test a screen before the return window closes. The good news: you don't need to install anything. A handful of full-screen solid colours will surface almost every common panel fault in about five minutes.
The panel faults worth checking for
Four issues account for most monitor complaints. Knowing what each looks like tells you which colour exposes it:
- Dead pixels. A pixel whose transistor has failed. It stays permanently off — a tiny black dot, most visible on white. Effectively unfixable.
- Stuck pixels. A pixel jammed on one colour, usually red, green or blue. It's still powered, which is why stuck pixels can sometimes be revived.
- Backlight bleed and IPS glow. Light leaking around the edges or corners, obvious as a cloudy glow on a pure black image in a dark room.
- Colour and brightness uniformity. Patches, tints or banding that show up on flat mid-tones like grey.
The test: full-screen solid colours
Put the screen into full-screen mode and cycle through pure colours one at a time, looking closely at each. Every fault reveals itself on a specific colour:
- Black — stuck/bright pixels (they glow) and, in a dark room, backlight bleed.
- White — dead or dark pixels, plus dust and smudges.
- Red, green, blue — subpixel faults. A pixel that looks fine on white can have one dead subpixel that only shows on its matching colour.
- Grey — the toughest uniformity test; tints and banding are easiest to spot here.
You can produce these colours any number of ways, but the quickest is a browser tool that fills the whole screen and switches between colours without menus in the way. A free one like BlankScreen does exactly that — pick a colour, click into full screen, and step through black, white and the RGB primaries in a couple of minutes, on any device with a browser.
Two things make faults far easier to catch: clean the screen first (a speck of dust looks just like a stuck pixel), and test bleed and uniformity with the lights off, at your normal brightness — cranking to 100% exaggerates bleed you'd never notice day to day.
Dead pixel or stuck pixel?
The distinction decides whether to attempt a fix or start a return. Show a white screen: a black dot is almost certainly a dead pixel. Show black: a coloured dot is a stuck pixel. Dead pixels don't respond to fixes; stuck pixels sometimes do.
Trying to revive a stuck pixel
No method is guaranteed, but two are worth a shot:
- Pixel-refresh cycling. Rapidly flashing colours over the stuck area can shock it back to life. Leave a colour-cycling video or utility running on the spot for 10–20 minutes.
- Gentle pressure. With the display on, place a soft, slightly damp cloth over the pixel and apply very light pressure with a fingertip. Go gently — too much force creates more dead pixels.
When is it a warranty issue?
This is where expectations meet reality. The old ISO 13406-2 standard (and the newer ISO 9241-307 that replaced it) defines pixel-fault "classes," and most consumer panels ship as Class II — which permits a small number of defective pixels before the panel counts as faulty. That's why a single stuck subpixel often won't qualify for a replacement.
Here's what each class allows, per million pixels:
|
Class |
Bright dots (stuck-on) |
Dark dots (dead) |
Stuck subpixels |
|
Class I |
0 |
0 |
0 |
|
Class II |
2 |
2 |
5 |
|
Class III |
5 |
15 |
50 |
|
Class IV |
50 |
150 |
500 |
Most consumer monitors are sold as Class II, which is why one stray subpixel usually isn't grounds for a swap — while a Class I "zero-bright-dot" panel gives you the strongest claim. Run the colour test before the return window closes, and you'll never be stuck arguing about it later.
Quick checklist
- Clean the screen.
- Full-screen white → black dots (dead pixels) and dust.
- Full-screen black, lights off → coloured dots (stuck pixels) and edge glow (bleed).
- Full-screen red / green / blue → subpixel faults.
- Full-screen grey → tints, patches and banding.
- Compare anything you find against the manufacturer's dead-pixel policy.
FAQ
Can I test a monitor without downloading software? Yes. Any source of full-screen solid colours works; a browser-based colour screen runs the whole check with nothing installed.
Will one dead pixel be covered by warranty? Often not — most consumer panels allow a few pixel defects under ISO class rules. Check your manufacturer's specific policy.
Can a dead pixel be fixed? No. A true dead pixel (permanently black on white) can't be revived. Only stuck pixels sometimes respond to pixel-refresh or gentle pressure.
