This backlight bleed test fills your screen with black and very dark grey, so light leaking in from the edges of an LCD panel shows up clearly. It works on LCD monitors, laptop screens and TVs, including IPS, VA, TN and mini LED panels, in any browser on Windows, Mac, ChromeOS and Linux. You can mark each bright patch, and the report lists where the leaks are, which is useful when you ask a seller for an exchange. OLED screens make their own light in every pixel and have no backlight, so they cannot bleed, but the dark grey patterns still show their near black faults.
How to test for backlight bleed
- Turn the room lights off and close the curtains, then give your eyes a minute to adjust.
- Set brightness to the level you normally use. Bleed grows with the backlight, so 100% makes every LCD look worse than it does day to day.
- Sit where you normally sit, centered, with your eyes level with the middle of the screen. Looking from close up or from an angle adds IPS glow, which is a different thing.
- Press Start full screen test. The black screen comes first. Look along each edge and into each corner.
- Press Space for 5%, 10% and 25% grey. Clouding and uneven patches are often easier to judge on dark grey than on pure black.
- When you see a leak, press M and click its brightest point. Each mark is listed with its position on screen, so you can describe it as top left or bottom edge in a claim.
Bleed, IPS glow or clouding?
| What you see on black | Moves when you move your head? | What it is |
|---|---|---|
| Bright patches spreading in from an edge or a corner | No | Backlight bleed |
| A silvery, bluish or warm haze in the corners | Yes, it grows and fades | IPS glow, normal for IPS panels |
| Blotches or a cloudy patch away from the edges | No | Clouding |
| Halos around bright objects on a dark background | Follows the objects | Blooming from local dimming on mini LED and other zoned backlights |
| An even dark grey instead of true black | No | The normal black level of an LCD |
The last row matters. An LCD cannot block all of its backlight, so black is a dark grey. IPS panels usually have a contrast ratio around 1000:1 and VA panels around 3000:1 or more, which is why VA blacks look deeper in a dark room.
Why LCD screens bleed
The liquid crystal layer of an LCD does not make light. A backlight shines through it, and the crystals block the light where the picture should be dark. In edge lit monitors and laptops, the LEDs sit along one or more edges and a sheet spreads the light across the panel. If the frame presses unevenly on the panel, or the layers are not perfectly flat, light escapes around the edges and shows as bright patches on dark content. Thin monitors and laptops, with tight frames and flexible lids, are the most prone.
Bright patches at the edges or corners
That is backlight bleed. Likely causes, from the most common:
- Uneven pressure from the frame. Normal variation between panels of the same model. An exchange may come back better or worse.
- Pressure on a laptop lid. Something left on the keyboard when the lid closes, or a tight bag, can press the panel and create new bleed.
- A knock or a bend. New bleed after a fall or a move points to physical damage.
What to do:
- Lower the brightness. Bleed shrinks in step with the backlight.
- Judge it in real use. Watch a dark film scene or play a dark game at your normal settings. If you do not notice it there, it is not worth an exchange.
- Within the store's return window, return or exchange a screen whose bleed bothers you in normal use. Makers rarely publish a bleed limit and often treat mild bleed as normal for an LCD.
- Leave the bezel alone. Loosening screws or pressing the edges sometimes reduces bleed and sometimes cracks the panel, and it can void the warranty.
A haze in the corners that changes as you move
That is IPS glow. It is light from the backlight seen at an angle through the panel, so it grows when you sit close to a large screen and moves as you shift your head. It is not a fault and an exchange will not remove it. Sit a little further back, keep your eyes level with the center, lower brightness at night, and add some light behind the monitor so the room is not pitch dark.
Cloudy patches or halos
Blotchy, cloudy areas away from the edges are clouding, common on large edge lit TVs and VA panels. Halos around bright objects on a dark background come from local dimming, where the backlight is split into zones much larger than a pixel. Set local dimming to a medium or low level if halos bother you, or turn it off to trade halos for greyer blacks. The hdr test shows bright highlights that make blooming easy to see.
How to photograph backlight bleed fairly
A phone camera in the dark raises its exposure until black looks grey, so every LCD looks far worse in a photo than in person, and sellers know it. For a fair photo:
- Turn off night mode on the camera.
- Tap the screen in the viewfinder and lower the exposure until the photo looks like what you see.
- Shoot from your normal seating position, centered, with the whole screen in frame.
- Take a second photo of a dark scene from a film or game at normal brightness, which shows whether the bleed matters in use.
Testing laptops, TVs and other screens
Laptop screens are edge lit and mounted in thin lids, so many show some bleed, often along the bottom edge near the hinge. Test with the lid at its usual angle. TVs are best tested from the sofa with the room dark, by opening this page in the TV's browser or from a laptop over HDMI. For the rest of the panel, run the dead pixel test for stuck pixels and the full lcd test for uniformity, gradients and sharpness. On an OLED, use the burn in test instead, since its greys show burn-in and near black banding.
What this test cannot do
A web page cannot measure light, so it cannot put a number on bleed. It gives you clean black and dark grey fields to judge by eye, which is how most sellers judge a return. If your browser cannot go full screen, the edges of the window are not the edges of the panel, so use a browser that can, or a full black screen in a full screen browser window.
Backlight bleed questions
How much backlight bleed is normal?
Almost every LCD lets a little light through at the edges on a black screen in a dark room. It counts as a problem when you notice it in normal use: dark film scenes, games or dark mode, at your usual brightness and seating position.
Can backlight bleed be fixed?
Not reliably. Lowering brightness makes it less visible. Loosening the bezel or pressing the edges sometimes helps but risks cracking the panel and voiding the warranty. On a new screen, an exchange within the return window is the safest fix.
Does backlight bleed get worse over time?
It can change a little as the panel warms up or the frame settles, but it rarely gets much worse unless the screen is knocked, flexed or pressed. A laptop lid that is often squeezed shut over something is a common cause of new bleed.
Do OLED screens have backlight bleed?
No. OLED screens have no backlight, so black pixels are simply off. They can show other near black faults, such as faint vertical bands or a tinted patch, which the dark grey patterns here reveal.
Is IPS glow a defect?
No. IPS glow is a property of IPS panels. It looks like a silvery or warm haze in the corners that changes when you move your head. Bleed stays in the same place wherever you look from.
Should I test at full brightness?
Test at your normal brightness first, because that is how you use the screen. Full brightness makes every LCD look worse. Check at 100% too if you play HDR games or work in a bright room.