Backlight Bleed Test
Show pure black and dark gray screens in full screen to spot light leaking at the edges (backlight bleed), angle-dependent glow (IPS glow), blotchy patches (clouding) and halos around bright objects (blooming). Mark what you see on the zone map to get a summary you can copy.
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In full screen: → Space or click next pattern, ← back, ↑ ↓ brightness, H hide hint, Esc exit. Swipe on touch screens.
Before you start
- Dim or switch off the room lights and close bright windows.
- Let the screen warm up for about 10 minutes.
- Use your normal brightness first; then try maximum to see the worst case.
- Sit at your normal distance, centered. Move your head later to tell IPS glow from bleed.
- Judge with your eyes. Phone cameras greatly exaggerate bleed and glow.
Mark what you see
Click a zone to cycle: none → slight → noticeable → severe.
How to use the Backlight Bleed Test
- Prepare: dim or turn off the room lights, let the screen warm up for 10 minutes and set brightness to your normal level.
- Press Start bleed test. The black screen fills the display and the cursor hides.
- Look straight at the screen from your normal viewing distance. Note bright patches at the edges and corners, then move your head: glow that changes with angle is IPS glow, light that stays put is bleed.
- Step through the patterns with the arrow keys, a click or a swipe: dark gray levels for clouding, letterbox for movies, the bright dot for blooming.
- Mark the zones on the map below the test and copy the summary if you need it for a return or warranty claim.
Bleed, IPS glow, clouding or blooming?
| Issue | What it looks like | Changes with viewing angle? | Best pattern |
|---|---|---|---|
| Backlight bleed | Bright patches or streaks along edges and corners | No, it stays fixed | Pure black, letterbox |
| IPS glow | Silvery or warm glow in the corners | Yes, shifts and fades as you move | Pure black |
| Clouding | Blotchy, uneven brighter areas across the screen | Barely | Dark gray 5% to 10% |
| Blooming | Halo of light around bright objects on black | No | Bright dot |
| Vignetting | Darker corners on gray screens | Partly (VA and TN panels) | Dark gray 15% to 20% |
Which screens are affected
- Edge-lit LCD monitors, laptops and TVs light the panel from the sides, so bleed at the edges and clouding are most common.
- IPS panels show IPS glow on dark content at an angle; VA panels have less glow but can show darker corners from gamma shift.
- Full-array local dimming and mini-LED screens have little edge bleed but can bloom around bright objects, depending on zone count and dimming settings.
- OLED screens light each pixel individually, so black is truly black: no bleed, glow, clouding or blooming. Use the dark gray levels to check for near-black uniformity issues and banding instead.
Testing tips
- Test at your normal brightness first: many panels show strong bleed only at maximum brightness in a pitch-dark room.
- Sit back to your usual distance; IPS glow is much stronger up close because the corners are seen at a steeper angle.
- If you photograph the screen for a return, set the camera to manual exposure close to what you see. Auto exposure turns mild bleed into dramatic glow.
- Recheck after a few days of use; slight bleed caused by pressure from the frame sometimes settles.
Frequently asked questions
What is backlight bleed?
Backlight bleed is light from an LCD's backlight leaking around the edges of the panel, where the panel and frame press unevenly. It shows as brighter patches, usually at the corners or along the edges, on a black screen. Unlike IPS glow it stays in the same place and keeps the same shape when you change your viewing angle.
How do I tell backlight bleed from IPS glow?
Move your head. IPS glow is a silvery or warm glow, strongest in the corners, that changes in brightness and shape as you change your viewing angle and is reduced by sitting further back. Backlight bleed stays fixed: same spot, same shape from any angle. A camera exaggerates both, so judge with your own eyes at a normal distance.
Is some backlight bleed normal?
A small amount of bleed or glow on a fully black screen in a dark room is common on edge-lit LCD monitors and laptops, especially IPS panels, and many manufacturers do not treat it as a defect. Bleed that is visible in normal use, during dark movie scenes with the lights on, or that is distracting at your usual brightness is a reasonable reason to request an exchange within the return period.
What is clouding?
Clouding is uneven, blotchy brightness spread across a dark screen instead of only at the edges. It is common on edge-lit LCD TVs and some monitors. Use the 5% to 10% gray levels to see it best; a uniform screen looks evenly gray everywhere.
Why test with a bright dot?
On screens with local dimming (full array or mini-LED backlights), the backlight behind a bright object turns up while the surrounding area stays dark. That creates a halo called blooming. Moving the dot around shows how big and how bright the halo is and whether the dimming zones lag behind. OLED screens light each pixel individually, so they show no bleed or blooming.
Can backlight bleed be fixed?
Sometimes it improves slightly by loosening the bezel screws or gently massaging the edge of the frame, but that risks damage and may void the warranty. Lowering brightness reduces how visible it is. If it bothers you, the safest fix is an exchange or warranty claim while you can still return the screen.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.