Backlight Bleed Test & IPS Glow Check

What this backlight bleed test checks

Every LCD monitor (IPS, VA and TN) relies on an LED backlight shining behind a liquid crystal layer. When the screen displays pure black, the crystals twist to block that light—but they never block 100% of it. Two completely different phenomena show up on a dark screen, and confusing them is the #1 reason monitor returns get rejected:

• Backlight bleed is a physical assembly defect where uneven bezel pressure or a warped frame lets raw LED light leak around the edge of the panel. It stays locked to the exact same spot on the bezel no matter where you move your head.
• IPS glow is an optical property of In-Plane Switching (IPS) polarizing films when viewed at an angle. Because the four corners of a 27-inch or 32-inch monitor sit at a steeper angle to your eyes than the center, the corners shimmer with a pale silver, amber or white haze—and that haze disappears as soon as you move your head directly in front of that corner.

Before you start

• Do NOT test at 100% brightness in a pitch-black room. Running a monitor at 350–400 nits in a dark room makes every edge-lit LCD on earth look defective and causes immediate eye strain. Set your monitor brightness to the level you actually use in a dim room (typically 25% to 50%, or roughly 100–140 nits).
• Turn off Dynamic Contrast and Local Dimming temporarily so the monitor doesn't shut off the entire backlight on a 0% black screen. (Using our 2% Near Black or 5% Clouding mode also defeats auto-shutoff.)
• Sit at your normal working distance—at least an arm's length (60–75 cm / 24–30 in) centered in front of the screen.

How to run the test

1. Dim your room lights and click Start fullscreen black screen test above.
2. Look at the center of the screen from 60–75 cm back. Note any bright spots along the top, bottom or corners.
3. Perform the head-tilt test: Lean your head 30 cm to the left and right, then stand up slightly so your eyes are level with the top corners. Watch whether the bright corners shift, shrink or vanish.
4. Press → in fullscreen to check 5% Dark Grey Clouding, which reveals blotchy mid-panel clouding (mura) even on panels that shut off their backlight on 0% black.
5. Press Esc and record the affected zones above to get your diagnosis and report.

How to read your results (Bleed vs IPS Glow vs Clouding)

When results can be misleading (especially phone photos!)

• Phone Night Mode overexposure: When you point an iPhone or Android camera at a black monitor in a dark room, the camera automatically turns on Night Mode (1–2 second exposure at ISO 3200) and tries to brighten the black screen into 18% middle grey. That makes a completely normal monitor look like it is on fire. To take an honest photo for an RMA, turn on our 3×3 zone grid, tap to focus on a grid line, turn Night Mode off, and lock exposure to roughly ISO 200–400 at 1/15 s shutter speed so the photo matches what your naked eyes see.
• Sitting too close to a 27–32" flat IPS panel: At 40 cm viewing distance, your eyes view the bottom corners at nearly a 35° diagonal angle, guaranteeing strong IPS glow. Moving back to 70 cm cuts that angle in half.

Backlight bleed test vs related tests

If you see a tiny, sharp pinprick of red, green, blue or white on the black screen instead of a soft glow, that is a stuck pixel—check it in our dead pixel test. To see how much your panel's contrast and colors shift off-axis across normal images, run the viewing angle test. And if dark movie scenes look blocky or washed out rather than glowing at the edges, check black level and RGB range in the monitor color test.

Frequently asked questions

Last reviewed: November 2026 · By the ScreenTestPro team