Screen Soft Light / Diagnostics / BACKLIGHT BLEED TEST

Dim the room, set brightness to maximum and sit straight on. Press F or tap Fullscreen. The panel text hides after a few seconds.

F goes fullscreen, Esc exits.

No. 001 · BACKLIGHT BLEED TEST

Backlight bleed test for laptops, monitors and TVs

  • 01 Pure black, full screen
  • 02 Bleed vs clouding vs IPS glow
  • 03 Works on any LCD

Check an LCD screen for backlight bleed, clouding and IPS glow with a pure black full screen. Dim the room, raise the brightness and look for light that leaks in along the edges and corners.

§ 01

Backlight bleed, clouding and IPS glow

Backlight bleed is light escaping at the edge of the panel, where the frame presses on the layers. It shows as bright strips or flashlight-shaped patches along one or more edges and does not move when you change your viewing angle. Clouding is the same cause spread over the middle of the screen: soft, uneven patches. IPS glow is different. It is a faint silver, white or warm haze that sits in the corners, gets stronger off-axis and fades or shifts colour when you move your head. IPS and VA panels both show it to some degree, and it is not a defect.

§ 02

No LCD is perfectly uniform.

What counts as a defect

No LCD is perfectly uniform. Faint leakage in a dark room at full brightness is normal. Worth a return: a bright patch you can see from your normal seat during dark scenes with a lit room, leakage that is clearly stronger on one side, or bleed that was not there when the unit was new. Judge it at the brightness you actually use. At 30 to 40% brightness most bleed disappears.

§ 03

Why OLED screens show nothing here

OLED and AMOLED pixels make their own light and turn fully off for black, so there is no backlight to leak. If an OLED shows a lit patch on black, it is a stuck pixel, a burn-in shadow or a reflection in the glass. Use the dead pixel test and the OLED burn-in test for those.

§ 04

Testing tips

Turn off any dimming or local-dimming mode first, since it can hide or exaggerate bleed. Close all other windows and hide the mouse pointer. Do not put your face close to the screen: bleed that only appears from a few inches away is not visible in use. For a laptop, open the lid to the angle you normally type at and test there.

Procedure

Three moves to peak output

  1. 01

    Warm up and dim the room

    Let the screen run for about 15 minutes, turn off the room lights and close the curtains. Daylight hides bleed completely.

  2. 02

    Maximum brightness, straight on

    Set the display brightness to 100% and sit centred, at the distance you normally use it. Tilt your head to separate glow from bleed.

  3. 03

    Go fullscreen and look

    Press F or Fullscreen. After a few seconds the buttons fade, leaving pure black. Note which edges or corners look lighter.

  4. 04

    Photograph it

    Put the phone on a steady surface, lock exposure and focus, and take one shot of the whole screen. Use the same settings if you compare two units.

Inquiries

Questions worth asking

Q.01 How do I test for backlight bleed?
Turn the room lights off, set the screen to maximum brightness, open the full-screen black test and view it straight on from a normal distance. Bright patches along the edges or corners that do not match the rest of the black are backlight bleed. Do the check after the monitor has warmed up for 15 minutes.
Q.02 What is the difference between backlight bleed, clouding and IPS glow?
Bleed is light leaking past the bezel edge, usually bright strips along one side or corner, and it stays put when you move your head. Clouding is soft, blotchy lighter patches spread across the middle of the screen. IPS glow is a faint silver or warm haze in the corners that shifts or fades as you change your viewing angle. Glow is a property of the panel type, bleed and clouding come from assembly and pressure.
Q.03 Is some backlight bleed normal?
Yes. Almost every LCD leaks a little light in a pitch-dark room at maximum brightness. It is a problem only when you can see it in normal use, for example in dark scenes with the room lit, or when it is strong enough to wash out a corner. OLED screens have no backlight, so they do not have bleed.
Q.04 Why does my phone photo of the black screen look worse than it does in person?
Camera sensors amplify dark areas and apply their own processing. Use a tripod or a steady surface, lock exposure, and compare photos taken under the same settings. Treat the photo as proof for a return, not as a measure of how bad it looks in person.
Cross-reference

Try adjacent plates