Black Screen Test
Fill the screen with pure black to find stuck pixels, backlight bleed and cloudy patches.
Every subpixel is off. Anything you can still see is light that should not be there — a stuck pixel, or the backlight leaking.
Looking at the whole screen, including the corners — what did you see?
How this test works
The page fills the display with #000000 and requests fullscreen, which turns every subpixel off. Anything you can still see is light that should not be there: a pixel stuck lit, or the backlight escaping past the edges of the panel. While fullscreen it measures how many device pixels it is painting against the resolution the panel reports, so a fill that is not reaching the corners cannot pass as a clean result. You report what you saw and the tool separates the three things a black fill can show — a stuck pixel, edge bleed, and mura in the middle — because they have different causes and very different warranty outcomes.
What the results mean
- Bright dot
- A pixel still lit on a black field is being driven but not changing. Stuck, not dead — and stuck pixels sometimes recover.
- Edge glow
- Light escaping at the borders is the backlight leaking past the panel. Normal in small amounts on any edge-lit LCD.
- Cloudy patches
- Uneven grey across the middle is mura, or the dirty-screen effect: the backlight is not even behind the panel. Nothing repairs it.
- Pixels painted
- Device pixels this fill is actually covering. Bleed lives in the corners, so a fill short of the edges misses the fault it is looking for.
Common problems and fixes
- The whole screen glows faintly
- On an IPS panel that is IPS glow, and it changes as you move your head — that is how you tell it from backlight bleed, which stays put. Neither is a pixel fault.
- I want to use this to turn my screen off
- A black fill is not the same as a display that is off: the backlight is still running on an LCD, so it still draws power. On an OLED the pixels genuinely are off and it does save power.
- The bleed looks terrible but only in this test
- Judge it at your normal brightness in a normally lit room, on real dark content. Maximum brightness on a pure black fill in the dark is the harshest possible condition.
Frequently asked questions
How much backlight bleed is normal?
Some is normal on every edge-lit LCD — it is a consequence of how the backlight is built, not a defect. The practical test is whether you can see it during ordinary dark-scene viewing rather than only on a black fill in a dark room.
What is the difference between IPS glow and backlight bleed?
IPS glow shifts and fades as you change viewing angle; backlight bleed stays in the same place no matter where you sit. Glow is inherent to the panel type, bleed is about how the panel is clamped in the frame.
Can a black screen test find a dead pixel?
No, and that is the point of running both. A dead pixel is already dark, so it is invisible against black. It only shows on white.
More in Device
- White Screen TestFill the screen with pure white to find dead pixels, surface dirt and uneven backlighting.
- Dead / Stuck Pixel TestFind dead and stuck pixels with fullscreen colours — and tell the two apart.
- Backlight Bleed TestCheck for backlight bleed on a full-black field — and tell it apart from IPS glow.