Backlight Bleed Test
Fill your screen with pure black and look at the edges: where the backlight escapes past the panel, you see it as a bright patch in the dark. The same black field also shows IPS glow and clouding, which look similar and mean very different things.
Before you start
- Turn the lights off. Bleed is a faint glow inside a black picture, and a lamp or daylight in the room hides it completely.
- Leave the brightness where you normally keep it. The amount of light that leaks grows with the backlight, so a screen turned up to maximum for the test looks far worse than the screen you actually use.
- Wait about thirty seconds once the screen is black. Your eyes need that long to adjust to the dark, and a good part of what people report as bleed fades away while they do.
- Sit straight in front of the screen at your normal distance. Light that only appears when you lean to one side is how the panel behaves at an angle, not a fault in it.
- Let the test cover the whole screen. A visible window, a taskbar or a bright wallpaper lights the panel from the inside and leaves nothing to judge. On iPhone and iPad the browser cannot take over the screen, so the page fills what it can and the outer edge stays behind browser chrome.
On an OLED screen there is nothing to see
An OLED has no backlight. Every pixel makes its own light, and a black pixel is switched off, so a perfectly even black field is the expected result and there is nothing to grade. This test is for LCD panels, which covers IPS, VA and TN, including the LED-lit ones sold simply as LED screens.
Frequently asked questions
What is backlight bleed?
An LCD pixel makes no light of its own. It filters a lamp that sits behind or beside the whole panel, and a black picture is that lamp blocked as well as the layers can manage. Where the frame does not hold those layers perfectly flat, usually at an edge or a corner, some light escapes around the filter and you see a bright patch in the dark.
Bleed, IPS glow or clouding - which one am I looking at?
IPS glow is a wide silvery haze in the corners that shifts, grows or fades as you move your head, and every IPS panel has some. Backlight bleed is a brighter patch or streak that starts at an edge and keeps its exact shape and position from every angle. Clouding, also called mura, is irregular blotches spread across the middle of the panel. Move your head first: whatever moves with you is glow.
How much bleed is normal?
Some is normal on almost every LCD, and a completely even black field is rare outside expensive panels with local dimming. What counts is whether you notice it while using the screen, not while staring at a black test image in a dark room with fully adjusted eyes. If it does not show up in a dark film scene or a night level in a game at your usual brightness, it is inside what this technology does.
Will the warranty cover it?
Often not, and it is better to know that before you start. Manufacturers publish counts for defective pixels, but very few name backlight bleed in a policy at all, so a claim is judged case by case by whoever reads it and mild bleed is usually called normal for the panel type. The realistic route is the retailer's return window, where a screen can go back because you are not happy with it rather than because it is broken. If you intend to try, do it early, photograph the screen and keep the packaging.