- Pure Black (Standard): The most common test. Look at the edges and corners of your screen. If you see clouds of white or yellow light leaking in, that is backlight bleed or IPS glow.
- 5% / 10% Dark Grays: Helps check for screen uniformity and "dirty screen effect" (DSE).
- Edge & Center Tests: Designed for modern TVs/Monitors with Local Dimming (FALD or Mini-LED). A white box or border forces the backlight to turn on in specific zones, allowing you to check for "blooming" or "halos" around bright objects on dark backgrounds.
- Controls: Click anywhere, or press Left/Right Arrows to switch between test patterns during the test. Press ESC to exit.
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What Is a Backlight Bleeding Test?
A backlight bleeding test shows dark, solid screens so you can spot light leaking around the edges of your display. On a screen that should look black, bleed shows up as pale patches, usually along the borders or in the corners.
This tool gives you five dark test patterns, a fullscreen mode, and an auto-cycle option. You can check a new screen right after unboxing, or see whether an older one has changed.
What Is Backlight Bleeding?
Many LCD screens use a backlight behind the panel. The panel is meant to block that light where the image should be dark. If light slips past the panel’s edges, it shows as bright patches on dark content.
Bleed is easiest to see when:
- The screen shows a black or near-black image
- The room is dark
- You are looking at the display from a normal distance
Screens that light each pixel individually, such as OLED, have no separate backlight. This test is mainly useful for backlit LCD displays.
How to Use This Backlight Bleeding Test
- Open the tool. It shows your current screen resolution and aspect ratio at the top.
- Pick a test pattern. Click one of the five thumbnails. The name of your selection appears below them as “Test Pattern.”
- Click “Start Fullscreen Test.” The pattern fills your screen so nothing else distracts you.
- Look closely at the edges and corners. Note any areas that look lighter or cloudy.
- Try the other patterns. Some leaks show up on one pattern and not another.
Want a hands-off run? Click “Auto-Cycle Patterns” and the tool moves through the patterns for you. If you are unsure how to set up your room or screen, click “How to Test Properly” for guidance.
The Five Test Patterns
The thumbnails show what each pattern looks like. Only the selected one is named in the interface, so the others are described by appearance.
| Pattern | What it looks like | Best for |
|---|---|---|
| Pure black | A fully black screen | Seeing the worst-case light leak |
| Near Black (5% Gray) | A very dark gray screen | Spotting leaks and uneven shading that pure black can hide |
| Dark gray | A slightly lighter dark screen | Checking how even the shading is across the panel |
| Black with a light border | A black screen with a thin light frame | Seeing the screen edges and checking that the image reaches them |
| Black with a small light square | A black screen with a gray square in the middle | Seeing how a bright object affects the dark area around it |
Start with pure black, then move to near black. Using several patterns gives you a fuller picture than one.
Tips for Getting an Accurate Result
- Dim the room. Turn off lights and close curtains. Ambient light hides bleed.
- Use fullscreen. Edges and corners are where bleed shows, so leave them clear.
- Check your brightness. Bleed looks stronger at high brightness. Test at the level you normally use, then again at a higher level.
- Sit at a normal distance. Don’t judge from a sharp angle, since most screens look lighter off-axis.
- Clean the screen. Smudges and dust can look like cloudy spots.
- Don’t judge with a photo alone. Phone cameras often exaggerate or hide bleed. Trust what you see in person.
Who Should Use This Test?
- New monitor or TV buyers. Check within your return window.
- Gamers and movie watchers. Dark scenes and letterbox bars make bleed easy to notice.
- Used-screen shoppers. Test before you pay.
- Anyone comparing screens. Run the same patterns on each and compare.
FAQs
Is some backlight bleeding normal?
A small amount is common on many LCD screens. What matters is whether you can notice it during normal use, such as dark movie scenes.
What is the difference between backlight bleed and IPS glow?
Bleed is light leaking at the edges, often in fixed patches. IPS glow is a soft sheen that tends to change when you move your head or viewing angle. If the patch shifts as you move, it is more likely glow than bleed.
Why does the test use “Near Black (5% Gray)” as well as pure black?
A near-black screen can reveal uneven shading that is hard to see on pure black. Using both gives you a better comparison.
Can I run this test on a laptop or phone?
Yes, if the screen is backlit and your browser supports fullscreen. The tool shows your screen resolution and aspect ratio so you can confirm what it detected.
Does bleeding get worse over time?
This tool can’t predict that. If you suspect a change, run the same patterns again later under the same conditions and compare.
What should I do if I find heavy bleeding on a new screen?
Check the seller’s return or warranty policy for your region. Note which pattern revealed it and take a photo for reference.