Backlight Bleeding Test

What is this tool?

Backlight bleeding is light escaping around the edges or corners of an LCD when the screen should be black. It happens because the backlight is always on behind the panel and the layers in front of it cannot block all of it perfectly.

The test fills the screen with pure black — the only field on which leakage is visible — and then walks you through a structured inspection rather than leaving you to stare at it. The page's own guide explains why black is used and why room lighting matters so much.

Crucially, it separates two things people often confuse. Backlight bleed stays in place as you move; IPS glow changes as your viewing angle changes. The five-angle sequence exists to tell them apart.

How to use it

1. Darken the room and set the room-light control to matchThe controls are Dark Room, Dim Room, Normal Room and Bright Room. Set what is actually true. Bleed is far more visible in the dark, so a bright-room inspection under-reports it and a dark-room inspection over-reports what you will notice day to day.
2. Set the brightness level honestly10%, 25%, 50%, 75% or 100%. Higher brightness means more light behind the panel and therefore more visible bleed. Test at the brightness you actually use, then at 100% to see the worst case.
3. Start the black test in fullscreenStart Black Test fills the screen. Fullscreen is essential — a taskbar or browser toolbar throws its own light and covers the top or bottom edge, which is exactly where bleed usually appears.
4. Let your eyes adapt for about thirty secondsDark adaptation takes time. What looks like a uniform black screen on first glance often reveals corner glow once your eyes have adjusted.
5. Work through the five viewing anglesCenter (direct eye line), then Left Angle, Right Angle, Up Angle (standing and looking down) and Down Angle (looking up). Use the Center, Left, Right, Above, Below and Previous controls. This is the step that distinguishes bleed from glow, so do not skip it.
6. Record what you observedThe report options name specific locations — each of the four corners, one or more edges, brightness that changes with viewing angle, cloudy dark areas, a centre darker than the edges, and general uneven brightness. Location is what makes the record useful later.

What the results mean

Screen appears uniformly black

No visible leakage at this brightness and room light. Retest at 100% brightness in a dark room before concluding the panel is clean — those are the conditions that expose bleed.

Backlight bleed (suspected)

A brighter patch at a corner or along an edge that stays in the same place regardless of where you sit. The page names this outcome directly. It is a manufacturing variance in how tightly the panel layers are held, and mild cases are extremely common.

IPS glow (viewing-angle effect)

A silvery wash that shifts or fades as you move your head. This is a property of how IPS panels handle light off-axis, not a defect, and it cannot be fixed. The page treats it as its own outcome for exactly that reason.

Clouding

Irregular lighter patches across the middle of the screen rather than at the edges. Different from bleed, which is edge-anchored. The Screen Uniformity Test inspects it more thoroughly across grey levels.

Center darker than edges

A vignetting pattern in the backlight rather than a leak. Worth recording, because it shows up in dark scenes and photo editing even when the corners look fine.

What it can detect

• Light leakage at specific corners, identified individually
• Leakage along one or more edges
• Brightness that changes with viewing angle — the IPS glow signature
• Clouding in dark areas
• A centre-to-edge brightness difference across the black field

Limits worth knowing

A browser can only report what the platform gives it. These are the honest boundaries of this page, so a result is never read as more than it is.

• The page's fifteenth guide section is “Browser Test Limitations”, and its FAQ asks both “Can a browser automatically detect backlight bleed?” and “Can this test measure backlight bleed in percentage?” No to both. No percentage, nit value or severity score is measured — the tool provides a pure black field and a structured way to look at it.
• Camera photographs exaggerate bleed dramatically. A long exposure collects light your eyes never notice, which is why photos of monitors look far worse than the monitors do. Judge with your eyes.
• OLED displays switch pixels off individually and have no backlight, so this test has nothing to find on them — the page's FAQ covers that too.
• Some panel variation is normal, and manufacturers publish their own acceptance criteria. Whether what you see justifies a return is a judgement against those criteria, not something this tool decides.
• The test only displays black. It cannot damage a display, as the page's FAQ states.

Tips

• Photograph it only for a record, never for judgement, and note the exposure. If you send a photo with a warranty claim, say what your eyes actually see as well.
• Test at your normal brightness first. Bleed you can only see at 100% brightness in a pitch-dark room is unlikely to affect your use.
• Check bleed after moving a monitor or unmounting it. Physical pressure on the frame can change it, sometimes for the better.

Troubleshooting

Related documentation

• DisplayScreen Uniformity TestA thirteen-step sequence across brightness, grey and colour fields, mapped to nine zones.
• DisplayDead Pixel TestFull-screen solid colours for finding dead, stuck and hot pixels by eye.
• DisplayScreen Flicker TestSteady and alternating fields for spotting flicker, at brightness levels you choose.
• DisplayDisplay Response Time TestControlled colour transitions for judging pixel response, trailing and overshoot by eye.
• DisplayMotion Blur TestMoving patterns at controlled speeds, so you can judge how sharp motion stays.