Backlight bleed test
Backlight bleed is the most common monitor defect there is, and the easiest one to miss, because it only shows on a black screen in a dark room. Four black levels, one after another, will show whether the light behind your panel is leaking where it should not.
The test opens full screen. Space — next · Arrow keys — back and forward · Esc — exit
Your browser blocked full screen. The test still works in this window, but a full-screen view is more reliable — try pressing F11.
Did you see light leaking in from the edges or corners?
How to test properly
This is the one test where the room matters more than the screen.
- Make the room as dark as you can. Not dim — dark. Bleed that is invisible with a lamp on will be obvious with it off, and you want to know it is there before you decide whether it bothers you.
- Let your eyes adapt for a minute. Your pupils need the time; judging in the first ten seconds will make you miss things.
- Sit at your normal distance, straight in front of the screen. Judging from 20 cm at an angle will show you glow that you will never see in use.
- Set the monitor brightness where you actually use it. Bleed scales with the backlight, so testing at 100% brightness when you work at 30% overstates the problem.
Press space to move through the four levels. Pure black first, then three very dark greys — this is what separates the two faults. Backlight bleed stays exactly as it is when the field lightens slightly. IPS glow fades away the moment there is anything at all on the screen.
Reading the result
| What you see | Where | What it is |
|---|---|---|
| Bright patch or streak with a hard edge | One or two edges | Backlight bleed |
| Broad silvery haze | Corners, changes with head position | IPS glow — normal |
| Even, slightly grey black | The whole screen | Panel black level — normal for LCD |
| Cloudy uneven patches across the middle | Middle of the screen | Clouding, a panel uniformity fault |
| Thin bright line along one full edge | One edge | Bleed from a pinched frame, often a shipping fault |
Windows 11
Switch off anything that lightens the picture before you judge:
- HDR must be off. With HDR on, the system may raise black levels, and you will be looking at the wrong thing entirely.
- Content adaptive brightness control on laptops actively brightens dark scenes. Settings → System → Display → Brightness.
- Night light does not affect bleed, but the warm tint makes a corner look brighter than it is.
macOS
- Turn off automatically adjust brightness in System Settings → Displays. On a black screen the ambient sensor will dim the backlight, which hides bleed.
- True Tone shifts the whole panel warm and makes edge leakage read as yellow rather than white. Off for this test.
If you are buying
Photograph the black screen with a phone if you may need to make a claim, but photograph it honestly: use a short exposure, hold the phone at normal viewing distance, and include something recognisable in the frame. A long-exposure photograph in a dark room makes every monitor on earth look defective, and support departments know it.
Common questions
What is the difference between backlight bleed and IPS glow?
Backlight bleed is light escaping around the edge of the panel where the frame does not seal properly. It looks like a bright patch or a streak, usually at an edge or a corner, and it stays in the same place whatever angle you look from. IPS glow is a property of how IPS panels handle light at an angle: it appears as a broad silvery haze in the corners, and it fades or moves as you change your viewing position. Bleed is a manufacturing defect; glow is normal and present on every IPS panel ever made.
How much backlight bleed is acceptable?
There is no published standard the way there is for pixel faults, which is exactly why bleed claims are difficult. The practical test manufacturers apply is whether it is visible in normal room lighting during normal use. Bleed that only appears on a pure black screen in a dark room is very unlikely to be accepted as a fault. Bleed you can see during a film with the lights on usually is.
Can backlight bleed be fixed?
Sometimes, and carefully. Mild bleed sometimes settles over the first few weeks as the panel and frame relax. Nothing else worth doing is a home fix — advice about massaging the panel with a cloth risks turning a cosmetic problem into dead pixels or a pressure mark. If it is bad enough to bother you, return it while you still can.
Why does my OLED screen show no bleed at all?
Because there is no backlight to leak. OLED pixels emit their own light and switch off completely for black, so bleed and IPS glow are both impossible. If you are testing an OLED, this test will look perfect — the faults worth checking there are burn-in and near-black uniformity instead.
Does bleed get worse over time?
It can. Heat cycling makes the frame expand and contract, and mounting pressure can shift. It rarely changes dramatically, but a screen that was borderline when new may be past your tolerance a year later — by which point the return window is long gone. That is the argument for testing on day one.