Backlight Bleed & Uniformity Test.
Fill your screen with pure black and near-black to reveal backlight bleed and IPS glow at the edges — then check mid-grey and white for clouding and the dirty-screen effect. Free, in your browser.
How to test backlight bleed and uniformity
Uniformity problems only show up on a plain, evenly-coloured field in the right lighting. A pure-black screen in a dark room exposes edge bleed and glow; a mid-grey or white screen exposes clouding and the dirty-screen effect. The method matters as much as the tool.
- 1. Darken the room. Bleed and glow are only visible with the lights off — in a bright room the backlight overwhelms them.
- 2. Start on pure black. Sit centred and about arm’s length away. Look at the four corners and edges for bright leaks (bleed) and a silvery corner sheen (glow).
- 3. Move your head. If a corner glow shifts or fades as your viewing angle changes, that’s normal IPS glow — not a defect. Fixed bright patches that don’t move are bleed.
- 4. Switch to grey and white. On the 25–50 % grey and white fields, look for cloudy blotches or a smudged, uneven texture — clouding and the dirty-screen effect.
Bleed, glow and clouding — and when it matters
Backlight bleed
Light leaking past the panel edges, seen as fixed bright patches or streaks on black. A small amount is normal on LCD/LED; large, distracting patches may justify a return or warranty claim.
IPS glow
A silvery-grey sheen in the corners of IPS panels that changes with viewing angle. It’s inherent to the technology, not a fault, and eases if you sit further back or centre yourself.
Clouding / mura
Uneven, cloud-like blotches across a dark grey field, caused by pressure or uneven backlighting. Mild clouding is common; heavy clouding on a new panel is worth flagging.
Dirty-screen effect
Faint smudges and uneven brightness on white or grey, most obvious on TVs during panning shots. It’s a uniformity flaw — annoying on some panels, invisible on others.
Test as soon as you unbox a monitor, laptop or TV, while you’re still inside the return window. Some sample-to-sample variation is normal, so judge whether it bothers you in real use rather than chasing a perfect panel.
What your results mean
Match what you see on the black, grey and white fields to what it means and whether it's worth acting on.
| What you see | What it means | What to do |
|---|---|---|
| An even, flat black with no bright patches | No backlight bleed — a good panel | Nothing to do. |
| Bright patches or streaks at the edges or corners on black | Backlight bleed — light leaking past the panel edge | A little is normal on LCD; if severe and new, return it. |
| A silvery corner sheen that shifts when you move your head | IPS glow — inherent to IPS, not a defect | Sit back/centre; nothing to fix. |
| Cloudy blotches on the 25–50% grey fields | Clouding / mura — uneven backlighting | Mild is common; heavy clouding on a new panel is worth flagging. |
| Hazy smudges or uneven brightness on white, worst during panning | Dirty screen effect (DSE) — a uniformity flaw, not dead pixels | Rule out real dead/stuck pixels with the dead pixel test. |
Frequently asked questions
How do I test for backlight bleed?
Dim the room as much as possible, launch the pure-black field full screen, and look at the edges and corners. Backlight bleed shows as bright patches or streaks — usually in the corners — where light leaks past the panel’s edges. A little is normal on LCD/LED screens; large, obvious patches that bother you in normal use may be a warranty issue.
What’s the difference between backlight bleed, IPS glow and clouding?
Backlight bleed is light leaking at the panel edges — fixed bright patches on a black screen. IPS glow is a silvery sheen in the corners that shifts or disappears as you move your head or change viewing angle — it’s normal for IPS panels, not a defect. Clouding (or mura) is uneven, cloud-like blotches across the middle of a dark grey field. Use the near-black and 25 % grey fields to tell them apart.
Is some backlight bleed normal?
Yes. Almost every LCD/LED panel has a little edge bleed — it’s a side effect of how the backlight is built. It only matters if it’s severe enough to distract you during dark scenes or in a dark room. OLED panels have no backlight, so they don’t bleed at all.
What is the "dirty screen effect"?
DSE is faint smudges, streaks or uneven brightness visible on a solid mid-tone — most obvious on white or grey, and on TVs during panning shots like sports. Open the white and 50 % grey fields full screen and look for a hazy, uneven texture. It’s a uniformity flaw rather than a dead-pixel fault.
Does it work on a phone, tablet or TV?
Yes — it fills any screen with a browser. It’s especially useful right after buying a monitor, laptop or TV, while you’re still inside the return window. Use the arrow keys or tap to switch fields, and Esc or the back button to exit.