Why LCDs show light on black
An LCD doesn’t make its own light. A backlight shines through a layer of liquid crystals that block or pass light for each pixel. That layer can never block light completely, and the backlight has to reach every edge of the panel, so a little light always gets through on a black screen. OLED screens work differently: each pixel makes its own light and switches fully off, so they don’t have backlight bleed.
Three things that look alike
| Backlight bleed | IPS glow | Clouding | |
|---|---|---|---|
| Where | Edges and corners | Corners | Anywhere, in patches |
| Looks like | Light leaking in from the frame | Silvery, bluish or warm sheen | Blotchy, uneven areas |
| Move your head | Stays put | Changes or fades | Mostly stays put |
| Cause | Pressure or gaps in panel assembly | Viewing angle of IPS panels | Uneven backlight, common on edge-lit TVs |
The head-movement check is the quickest way to tell them apart. IPS glow is a property of the panel type and is visible on virtually every IPS screen to some degree. Bleed and clouding vary from unit to unit.
How to test fairly
- Use your normal brightness, not maximum. Bleed that only appears at full brightness in a pitch-black room may never bother you.
- Turn off local dimming, HDR and dynamic contrast. They can dim the backlight on a black screen and hide what you’re checking.
- Dim the room and give your eyes a minute to adjust.
- Open the backlight bleed test, go fullscreen and look from your usual seat, then step through the near-black grays.
- Move your head left, right, up and down to separate glow from bleed.
Don’t trust a phone photo
Phone cameras brighten dark scenes automatically, so photos make bleed look many times worse than it is. If you need a photo for a return, lower the exposure until the photo looks like what you see with your eyes.
What you can do about it
- Lower the brightness a little. Bleed shrinks quickly as brightness drops.
- Add some room light or a bias light behind the monitor. Both make glow and bleed much less noticeable.
- Sit centred and at a sensible distance to reduce IPS glow, which grows at steep angles.
- Avoid DIY fixes like loosening screws or pressing on the frame. They can make things worse and may void the warranty.
Should you return it?
Every manufacturer judges bleed differently, and some amount is considered within spec. If bleed is distracting in normal use at normal brightness, a return within the retailer’s window is often the simplest route, since another unit of the same model can be noticeably better. If you prefer deep blacks above all, an OLED or a mini-LED screen with full-array local dimming is a better fit than another edge-lit LCD.