Backlight Bleed Test
Show full-screen black and dark grays to spot backlight bleed and IPS glow on an LCD.
Blooming Test
Check an LCD with local dimming, such as a mini-LED monitor or TV, for blooming: halos of light around bright objects on a black screen. In a dark room, press Start test, then drag the shape or watch the moving patterns.
Showing Square · 1 of 7
Drag the square around and watch the black beside it. A glow that spreads past its edges and follows it is blooming.
The size of the shape, the dots, the stars, the subtitle text or the bright band.
The gray of everything drawn, as a share of full white: a signal level, not light output.
Runs entirely in your browser. Test results, audio and video never leave your device.
How to test a screen for blooming
- Dim the room and set the brightness you normally use. If the screen has a local dimming setting, note what it is set to.
- Choose Square, Circle or Dot, set Size and Brightness, then press Start test or click the preview to fill the screen.
- Drag the shape slowly across the screen, or move it with the arrow keys (hold Shift for bigger steps). A glow around it that follows it is blooming.
- Press Next or Space to go on to Moving dot, Starfield, Subtitle bar and Bright edge. On these, the arrow keys and a tap also change the pattern, and Pause stops the motion.
- Change the local dimming setting, for example from High to Low or Off, and check again. Halos usually shrink as it goes down, while black turns grayer. If nothing changes, the screen may not be dimming its backlight for this content.
- Press Esc or Exit to finish.
What is blooming on a monitor or TV?
Blooming is a halo of light around bright objects on a dark background, seen on LCDs with local dimming, including mini-LED screens. Each backlight zone is far larger than a pixel, and the LCD cannot fully block a lit zone's light, so black pixels near a bright object glow. Edge-lit dimming blooms too, often in bands. OLED has no backlight zones, so it does not show this halo.
Blooming vs backlight bleed vs uneven gray
Blooming moves with bright objects. Light that stays at the edges of an all-black screen is backlight bleed, which the Backlight Bleed Test checks, and blotches on a flat gray screen are a uniformity problem for the Screen Uniformity Test.
| What you see | When a bright object moves | Found on | |
|---|---|---|---|
| Blooming | A glow or halo around bright objects on black | Moves with the object | LCDs with local dimming |
| Backlight bleed | Bright patches at the edges or corners of a black screen | Stays in place | Any LCD |
| Uneven gray (clouding) | Lighter and darker blotches on a flat gray screen | Stays in place | Mostly LCDs |
How to reduce blooming
Blooming comes from local dimming, so the screen's own settings control it, where it has them. Compare them on the same pattern, such as the Subtitle bar:
- Lower the local dimming level, or turn it off. Halos usually shrink, but black turns grayer; the Contrast Test shows how dark black gets.
- Try each picture mode you use. Game, PC and Movie modes can use different dimming levels.
- Lower the brightness or backlight, and add some light to the room. Both can make halos less visible.
- Update the screen's firmware. Makers sometimes change how dimming behaves in updates.
How much blooming is normal?
Some blooming comes with local dimming: even thousands of zones are far fewer than the millions of pixels. More, smaller zones and better dimming processing usually mean smaller halos, but none remove them. Judge it the way you watch: at your usual brightness and distance, on subtitles, dark game menus or a starry scene.
For the 12.9-inch iPad Pro (5th and 6th generation), Apple's support page says bright LEDs can cause a slight blooming effect, and calls a slight blur or color change while scrolling against black backgrounds normal behavior. Sellers and makers decide what counts as a defect, so if halos bother you in everyday content at every dimming level, raise it with the seller while the return window is open.
What this test can detect
- Halos: a gray glow around the Square, Circle or Dot that spreads past its edges and moves with it as you drag it.
- Zone switching: a halo that trails the Moving dot, moves in steps, or turns brighter and dimmer as the dot travels. A trail behind a moving object can also be motion blur, which the Ghosting Test covers.
- Gray patches around the stars of the Starfield, or faint stars that fade or brighten as they drift.
- A gray haze around the white text of the Subtitle bar, as around subtitles in a dark film.
- Light spreading past the Bright edge, or a lighter band running across the screen from it: edge-lit dimming often blooms in bands.
How it works
Each pattern is drawn on a canvas sized to the device pixels of the test area, on pure black (#000000). Brightness sets the gray of everything drawn, from 10% (#1a1a1a) to 100% (#ffffff): signal levels, not light output. Size has 5 steps; the Square runs from 4% to 40% of the screen's shorter side.
The Moving dot travels about 12% of the shorter side a second and the 140 stars drift 1.2% of the width a second; nothing flashes and nothing is measured. Where the browser has the Screen Wake Lock API, the page asks it to keep the screen on during the test.
Limitations
- The page cannot switch local dimming, count its zones or measure a halo. It draws the patterns; your eyes judge them, and the screen's own settings decide how it dims.
- These patterns use ordinary SDR colors, which may not trigger the HDR dimming of a TV or monitor, so blooming in HDR films and games can look different. With Windows HDR on, the SDR content brightness slider changes how bright these patterns look and how much they bloom. The HDR Test helps you check whether HDR is active.
- The floating control bar and the mouse pointer are bright too, and can light zones of their own. Both hide after 2.5 seconds without input, so wait a moment before judging.
- Where the browser has no fullscreen mode, such as Safari on iPhone, the test fills the browser window and the browser's own bars stay lit.
- Bright white on black can be glaring in a dark room; lower Brightness if it is uncomfortable. Nothing flashes, the moving patterns are slow, and with reduced motion they start paused. Do not leave a still shape on an OLED screen for hours.
Frequently asked questions
Do OLED screens have blooming?
OLED has no backlight zones, so it does not show this halo. Each pixel makes its own light and can switch off completely for black. OLED has other trade-offs, such as burn-in, which the Screen Burn-In Test checks.
Why does blooming look worse in photos?
A phone camera raises its exposure in a dark room, so a faint halo turns into a bright one, and its processing can add glow of its own. Judge with your eyes at your normal viewing distance. If you need a photo for a claim, lower the exposure until the photo matches what you see.
How many dimming zones does my screen have?
The page cannot tell you. Some makers list the zone count in the specifications. Moving the Dot slowly shows roughly how far each halo reaches, but dimming processing can blend neighboring zones, so they cannot be counted reliably by eye.
Can I test a TV or tablet for blooming?
Yes, if it has an LCD with local dimming. Among iPads, only the 12.9-inch iPad Pro (5th and 6th generation) has one; iPad Pro models released since 2024 use OLED. On a TV, open this page in its browser or connect a computer by HDMI, then press Start test; on a touch screen, drag with one finger to move the shape.