Black Screen Test: Full Black Screen for Dead Pixels
Black Screen Test. Click Start Black Screen Test to fill your display with pure black and spot stuck pixels and backlight bleed. The white screen test runs fullscreen so you can inspect your panel edge-to-edge under real viewing conditions.
Interactive Tool
The custom color is also the last pattern in the fullscreen test (pick it there with the color picker in the controls bar).
Black Screen Test switches your entire display to pure black so you can check for stuck bright pixels, backlight bleed, IPS glow, and panel clouding — the flaws a lit-up desktop always hides. On an OLED panel any light you see against true black is a real defect, since OLED pixels switch off completely, while a little glow near the edges of an LCD is normal backlight bleed; click Start Black Screen Test in a dark room for the clearest read, and use the arrow keys to cycle onward.
Lights off and an online black screen test are all you need to vet a new screen before keeping it. The page fills your display with #000000, and in under 60 seconds any lit dead pixels or glowing corners stand out against the pure black fullscreen. It works on monitors, smartphones, tablets and TVs, and the payoff is a clear answer on whether your screen is defect-free.
What a Black Screen Test Shows You
A black screen check is the quickest display test you can run: every pixel is told to show black, so anything still emitting light is a fault. It doubles as a monitor test for light leakage, screen uniformity and the pixel defects a busy desktop hides, and it's a fair first read on display quality. Run your input through the stuck pixel fixer tool to get a detailed breakdown in seconds.
- A bright dot that never changes: a lit fault that won't clear.
- Light pooling at one edge that stays put when you move: backlight bleed.
- A soft haze in the corners that shifts with your head: IPS glow.
- Cloudy patches across the middle: poor uniformity.
Why a Pure Black Display Exposes Defects
On a pure black display the background luminance drops to almost nothing, so one lit point has extreme contrast. An OLED is self-emissive and reaches true black by switching off, while a backlit screen can only block its light, so results differ between the two.
How to Run a Full Black Screen in Fullscreen Mode
The full black screen takes seconds to set up, but the order matters.
- Dim the room and close the curtains.
- Wipe the glass so dust isn't mistaken for a defect.
- Open the tool in your browser and click the black box to enter fullscreen mode.
- Raise brightness to maximum and wait while your vision adjusts.
- Scan the edges first, then the centre, row by row.
The steps are the same on laptops and on a smartphone; on a phone, turn off auto-brightness first.
Exiting Black Screen Mode
Press the Esc key to leave black screen mode. On a phone or tablet, tap or swipe down from the top to bring the controls back.
Black Screen Video vs a Black Image
A static black image costs your device almost nothing to show. A looping black video does the same job but keeps the decoder busy, using more memory and power. For a long black screen session, the static image is the better choice.
Features of a Good Black Screen Tool
Any black screen test tool should get out of your way fast. Look for: The blue screen test is free and runs entirely client-side, so nothing about your display is ever uploaded.
- Solid black at #000000, not a dimmed gray theme.
- A color picker or hex code field for white and single-color fields.
- A timer that exits after a set time, which protects OLED screens.
- Free to use, with no download and no sign-up.
Pixel Defects a Black Background Reveals
On a black background, faults show up as bright pixels: points that should be off but aren't. A 24-inch 1920×1200 monitor carries 2,304,000 of them and a 4K screen 3.6 times as many. Each has three sub-pixel elements.
Dead Pixels vs Stuck Pixels
Dead pixels have a failed transistor, so no power reaches them. The thin-film transistors (TFT) behind each point switch it, and when one fails the dot stays dark on every color. That's why a dead pixel barely shows on black and is easiest to spot on white. Stuck pixels are the reverse: one of the red, green, and blue sub-pixels is locked on, so a colored dot glows against black. A pixel fixer running rapid color cycling can sometimes revive a stuck one; a dead one never recovers.
Is It a Hot Pixel or a Stuck Pixel?
A hot pixel glows white on every color, while a stuck pixel holds one color. Both show on black. Faults can appear months after purchase, so rerun the check before your warranty ends.
Backlight Bleed vs IPS Glow on a Black Screen
Almost every LCD leaks some light on black. The question is whether it's backlight bleeding, a defect, or IPS glow, a trait of the technology.
| Sign | Backlight bleed | IPS glow |
|---|---|---|
| Where it appears | Fixed bright patches along the edges | Soft haze in the corners |
| Viewing angle | Stays in place when you move | Shifts and fades as you move |
| Cause | Uneven bezel pressure on the backlight layer | How the liquid crystal layer passes light off-axis |
| Warranty claim | Often valid if visible in normal use | Rarely accepted |
| What helps | Exchange or RMA | Lower brightness (fewer nits) and some room light |
The Viewing Angle Test
With the black screen up, look at the bright area and move your head slowly to one side. If the glow slides or changes tint, it's IPS glow. If it stays fixed, it's backlight bleeding from the panel assembly, and that's what you photograph.
Light Patches and Uneven Gray
If the black screen shows cloudy patches, confirm them on a mid gray background. Blotches or bands there are the dirty screen effect, from an uneven diffuser. Patches visible in normal video are worth documenting.
OLED vs LCD on a Dark Screen
A dark screen also reveals your panel technology. With the lights off, an OLED looks as black as the bezel. An LCD or LED-backlit screen shows a faint glow, because the backlight never turns off and the liquid crystals only block most of it.
Why an LCD Shows Dark Gray Instead of Black
That gray is normal. IPS, VA and TN designs all leak light, with VA usually darkest. A budget laptop with a 6-bit panel tends to look worse, since thin chassis press unevenly on the backlight. Gray alone isn't a defect; uneven gray is.
OLED Burn-In and Image Retention
Static images held for hundreds of hours, such as a taskbar or a channel logo, wear OLED subpixels faster and leave a permanent ghost: OLED burn-in. Ghosts show on a gray field rather than on black, and image retention fades while burn-in doesn't. Running a black screen is safe, since unlit cells carry no voltage stress; pixel shift and an auto-hiding taskbar slow the wear. Older plasma TVs suffered the same way from any static image.
Running a Black Screen Check on a 16-Inch Laptop Before Day 14
I'm deciding whether to keep a 16-inch 2560×1600 notebook bought for photo culling, and the retailer's no-questions return ends on day 14. It's day 3. The answer arrives early: one stuck green dot and a mild lower-left wedge of bleed, both tolerable, so I keep it, but getting there takes a few measured steps.
First I work out how close I need to sit. The diagonal is 3,018.9 dots across 16 inches, so 188.7 PPI and a 0.135 mm pitch; divided by tan(1/60°), that's 46.3 cm. A lit fault on the black pass shows from my 55 cm typing position anyway, but a dark one could hide at that distance, so I lean in to roughly 23 cm for the white pass.
Lights off, fullscreen black at maximum output, five minutes of sitting in the dark. One green dot sits 4 cm in from the right bezel, a third of the way down. I wipe the glass and it stays; on a green field it vanishes, which marks it as a stuck green element rather than a smudge. The lower-left wedge doesn't move when I shift my head, so it's bleed, not glow.
Then the threshold. The screen has 4,096,000 dots (I recompute 2560 × 1600 by hand so the allowance rests on the right resolution). Class II allows 5 faulty single-color elements per million, which is 20.48, so 20 here. One is nowhere near a failing count.
| Same 16-inch size | 2560×1600 | 3840×2400 |
|---|---|---|
| PPI | 188.7 | 283.0 |
| One-dot visibility distance | 46.3 cm | 30.9 cm |
| Single-color faults allowed | 20 | 46 |
The comparison is the number I'd watch: on the denser version the black screen still catches lit faults, but dark ones vanish at typing distance, so the white pass becomes essential.
The catch is the bleed. It's obvious at full output and gone at the 35% level I edit at, and the defect standard counts dots, not light leaks, so it can't settle this part for me. My rule: if a 2.5-second manual shot at my working setting doesn't show it, it doesn't justify a return. I save that shot and rerun the black screen test on day 12, two days before the deadline, to confirm the stuck element hasn't spread to a neighbour.
Black Screen Testing Tips for Accurate Results
Run the first pass at full brightness, then repeat at the level you actually use, since a patch only matters if it shows up in everyday viewing.
Dark Room and Dark Adaptation
Test in a dark room at night or with blackout blinds, because ambient light reflecting off the glass hides faint bleed. Let the display warm up for ten minutes and give your eyes about five minutes of dark adaptation before judging.
Viewing Distance for Spotting Dead Pixels
On the black screen a lit fault shows from any normal distance; the white follow-up pass is where distance matters. Eyesight resolves about one arcminute, so:
$$\text{PPI} = \frac{\sqrt{w^{2} + h^{2}}}{d} \qquad \text{pitch} = \frac{25.4}{\text{PPI}} \qquad D = \frac{\text{pitch}}{\tan(1/60^{\circ})}$$
Take a 24-inch monitor at 1920×1200. Its diagonal is 2,264 points long, giving 94.3 PPI and a 0.269 mm pitch, and dividing by \(\tan(1/60^{\circ})\) gives about 93 cm. To find dark dead pixels on white, sit at roughly half that viewing distance. A 32-inch 4K gaming monitor brings the figure down to about 63 cm.
Following Black with a White Screen and Color Fields
Black only finds lit faults. Follow it with a white screen for dark ones, then single-color fields for faults that show in one color. Those five fields make a complete dead pixel test.
Calibration and the Break-In Period
Rerun the black screen before and after calibration, because adjusting brightness and contrast can expose or hide faint bleed and shifts the color balance in dark tones. Mild bleed sometimes eases during a break-in period of a few weeks, so recheck it on black later.
When a Black Screen Defect Counts Under ISO 9241-307
A perfect panel isn't guaranteed. ISO 9241-307 sets defect limits, and most consumer monitors are Class II, which allows per million pixels up to 2 always-on, 2 always-off and 5 faulty sub-pixel spots. Scaled to the 24-inch 1920×1200 example, that's about 4 bright and 4 dark points before it fails. A few product lines carry zero-defect promises, and tight clusters count as a manufacturing defect sooner.
Dead Pixel Policy and the Return Window
The return window is your best leverage: a retailer will usually swap a unit no questions asked. After that, the manufacturer's dead pixel policy and warranty decide, and an RMA can take weeks. Run the black screen check on day one so any replacement is easy.
Documenting Defects with Photos
Photograph the fault with the black screen still up. Phones underexpose dark scenes, so for backlight bleed use manual mode with a longer exposure and fixed shutter speed. Use macro mode for a single dot, and shoot the serial number label too.
Plain Black Screen for Screen Cleaning
A plain black screen is also the best backdrop for screen cleaning. Dust, fingerprints and streaks hide on a busy desktop but light up against black. Wipe with a dry microfiber cloth and look again.
Pure Black Screen for OLED Power Saving
On OLED and AMOLED screens, black areas draw close to zero power, so a pure black screen costs almost nothing. Keeping one up while music plays cuts power consumption and stretches battery life, and some phones also drop the refresh rate on a static frame. On a backlit screen the lamp keeps burning, so energy use barely changes.
Other Uses for a Blank Black Screen
A black fullscreen has plenty of non-test uses: blanking a second monitor during a film, giving a projector a dark frame, checking color spill in video editing, or darkening a TV that is only playing audio. A black screen tester tab handles all of them.
Can a Black Screen Work as a Screensaver?
On OLED, yes, since unlit areas won't burn in. On a backlit screen it saves almost nothing, because the backlight stays on.
Frequently Asked Questions
- How long should a black screen test take?
- A first pass takes about a minute once your eyes have adjusted to the dark. For a careful check, scan each part of the screen in turn for a few minutes, then repeat with white, red, green and blue.
- Why does my LCD look gray instead of black?
- An LCD's backlight stays on and the liquid crystals can only block most of its light, so black shows as a faint gray. That's normal. Uneven bright patches at the edges point to backlight bleed instead.
- How do I tell backlight bleed from IPS glow?
- Move your head to one side while the black screen is up. Glow that shifts or changes tint is IPS glow, a trait of the panel. Light that stays fixed in the same spot is backlight bleed.
- Can a black screen damage an OLED display?
- No. Black pixels on an OLED are switched off, so they carry no voltage stress. Bright static content is what causes burn-in; the timer just makes sure no test color is left on screen for hours.
- How many dead pixels are acceptable on a new monitor?
- It depends on the manufacturer's dead pixel policy. Many follow ISO 9241-307 Class II, which tolerates a few faulty pixels per million, while some premium lines promise zero defects. Test during the return window, when swaps are easiest.
- How do I exit the full black screen?
- Press Esc on a keyboard. On a phone or tablet, tap the screen or swipe to bring the controls back.
- Does a black screen save battery?
- On OLED and AMOLED screens, yes: black pixels draw almost no power. On an LCD the backlight keeps running, so the savings are small.