# Backlight bleed test

The backlight bleed test shows black and dark gray to reveal light leaks at the edges, IPS glow, clouding and blooming. No install needed.

Open the test: https://setupcheck.app/backlight-bleed-test/

## How to use the backlight bleed test

1. Follow the **Before you look** checklist on this page: darken the room, wipe the screen with a dry microfiber cloth and turn the brightness up to maximum.
2. Click **Start backlight bleed test**. The screen fills with black. Watch the edges and the corners.
3. Tap the right side of the screen, or press **→** or **Space**, for the next shade. Gray 2%, Gray 6% and Gray 10% follow the black. Tap the left side or press **←** to go back, and press **Esc** or click **Exit** when you are done.
4. Under the test, answer the four checks with what you saw: None, Slight or Obvious. Click a selected answer again to clear it.

Then lower the brightness to the level you normally use and run the shades again. Whatever you can still see is what you will notice day to day. If you have a mini-LED screen or another screen with local dimming, click **Start blooming test**, move the white dot with the mouse, a finger or the arrow keys, and look for a halo around it. The summary is built only from your answers.

## What the results mean

The test shows the screen, you judge what you see, and the page sorts your four answers into a summary.

| What you see | What it means | What to do |
|---|---|---|
| Bright, often yellowish or white patches at the edges or in the corners that stay put when you move your head | Backlight bleed: light leaks out where the frame presses on the panel or its layers are uneven. | Slight bleed is common on LCD screens. Obvious bleed is worth a return or an exchange while the store allows it. |
| A silvery, bluish or warm sheen in the corners that grows, shifts or fades as you move your head or your distance | IPS glow. It comes with the IPS panel type, not with your unit. VA screens can show a weaker version. | Normal for the panel type, and an exchange will not remove it. Sit square in front of the screen. |
| Uneven, blotchy patches across the screen, easy to see on the dark grays | Clouding: the backlight is uneven across the panel. | Slight clouding is common. Treat obvious clouding like obvious bleed. |
| A halo around the white dot on black | Blooming: the local dimming zones are larger than the dot, so light spills into the black around it. OLED screens have none. | A property of the technology. Try the local dimming setting in the screen’s menu, if it has one. |
| Nothing on any shade | No sign of the four effects at your brightness and angle. | Answer None for each check. The summary shows All clear once bleed and clouding are answered. |

The four shades are exact grays, so each one shows something different:

| Shade | Value | What it shows |
|---|---|---|
| Black | 0 of 255 | Bleed and IPS glow show most clearly here. |
| Gray 2% | 5 of 255 | Some screens turn the backlight down on a fully black picture, which hides bleed. This near-black gray usually keeps the backlight on. |
| Gray 6% | 15 of 255 | Clouding and other blotches. |
| Gray 10% | 26 of 255 | Clouding and other blotches. |

The percentages are shares of the 0 to 255 signal range, not of the light the screen gives off, which is far lower.

The **Summary** has three verdicts. **Worth reporting** appears when bleed or clouding is Obvious. **Typical** appears when you saw anything else: slight bleed or clouding, or glow or blooming at any level, because those come with LCD screens. **All clear** needs bleed and clouding answered and every answer None. With no answers, or with only None answers that leave bleed or clouding open, the summary just asks for answers.

**Dynamic range** says whether your screen and the browser report HDR. On Windows the screen also needs HDR turned on in the system. The shades are drawn in standard range, so blooming often looks stronger in HDR films and games. **Rendering resolution** is the screen size in CSS pixels times the device pixel ratio.

If you found bleed or clouding:

- **Take a photo** with the exposure set to match what you see. It helps with a return or a warranty claim.
- **New screen?** Check the store’s return period first. A return or an exchange is often quicker than a warranty claim.
- **Warranty:** each manufacturer decides how much bleed counts as a defect. Many treat slight bleed and IPS glow as normal.
- **Do not press** on the edges or loosen the frame. It can damage the panel and void the warranty.

## Backlight bleed test not working?

The test asks for no permission, so it has few ways to fail.

### Full screen does not start

The test asks the browser for real full screen when you click **Start backlight bleed test**. If the browser refuses, for example inside an embedded frame, the test fills the page with a fixed layer instead. The browser bars then stay on screen and the pixels under them are not tested. Safari on the iPhone puts only videos into full screen, so there the test is always a layer; turn the phone sideways to hide most of the bars. On a computer, press F11 (Windows and Linux) or Ctrl + Cmd + F (Mac) to hide the bars first.

### A gray looks exactly like black

Your screen or its settings hide the darkest shades. That is not bleed. A computer sending full-range color to a monitor that expects limited range, a low black level or gamma setting, and night or eye-care modes can all do this. Judge clouding on the lightest gray, Gray 10%, and check the black level or the RGB range (full or limited) in the monitor and graphics settings.

### No halo around the white dot

That is expected on OLED screens and on LCD screens without local dimming. If your screen has local dimming, check that it is switched on in the screen’s menu. Some screens use it mainly in HDR, and the dot is drawn in standard range, so the halo can look smaller here than in HDR films and games.

### The summary shows no verdict

The summary stays on its prompt while there is nothing to judge: no answers yet, or only None answers without both bleed and clouding answered. It measures nothing itself. Choose None, Slight or Obvious for at least bleed and clouding, and click a selected answer again if you want to clear it.

### The Exit button is missing in the blooming test

Moving the dot does not bring the controls back, because the bright buttons would bloom themselves. Tap or click once, or press any key except an arrow, to show **Exit**. **Esc** leaves at once.

## How we measure

The test measures nothing about the panel: it fills the screen with exact grays (#000000, #050505, #0f0f0f and #1a1a1a), or draws a white dot on black that is 3% of the shorter screen side wide, between 16 and 40 px, and you judge by eye. The summary comes only from your four answers, and the page cannot tell whether they are right. Dynamic range comes from the `(dynamic-range: high)` media query, and rendering resolution is the screen size in CSS pixels times `devicePixelRatio`. A browser cannot read the light the screen gives off or how evenly it spreads, so the test gives no brightness or uniformity figures, and the room, the brightness and your viewing angle are part of the result.

## Frequently asked questions

### Does an OLED screen have backlight bleed?

No. Each OLED pixel makes its own light, so there is no backlight to leak, no IPS glow and no blooming. The dark grays of this test can still show uneven patches near black on an OLED screen, but those come from the panel and are not bleed.

### Is IPS glow the same as backlight bleed?

No. IPS glow is a sheen in the corners that changes size and color as you move your head or your distance, and it comes with the IPS panel type, so every unit of a model shows it. Bleed is a bright patch at an edge that stays where it is, and it differs from unit to unit. Move your head to tell them apart.

### How much backlight bleed is normal?

A little is common on LCD screens, and each manufacturer decides how much counts as a defect. The test treats slight bleed as typical and obvious bleed as worth reporting. If you see it only at maximum brightness in a dark room, it rarely matters in daily use, so look again at the brightness you normally use.

### What brightness should I use for a backlight bleed test?

Start at maximum brightness in a dark room, which makes any leak easy to find but also exaggerates it. Then repeat at the level you normally use, because only what shows there matters day to day. If bleed seems to vanish on pure black, a dynamic contrast or local dimming setting may be turning the backlight down, which is why the test also shows Gray 2%.

### Can backlight bleed be fixed at home?

Not safely. Bleed comes from how the panel sits in its frame, and pressing on the edges or loosening the frame can make it worse and void the warranty. A return, an exchange or a warranty claim is the way to go. Bleed differs between units of the same model, so after an exchange run the test again in the same room and at the same brightness.

### Why does backlight bleed look worse in a phone photo?

Phone cameras brighten dark scenes, so a photo of a black screen shows far more bleed than your eyes do. Judge by eye. If you need a photo for a return or a warranty claim, set the exposure by hand until the photo looks like what you see.

Updated 2026-10-08

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