InputChecksWhat this blooming test checks
A blooming test looks for a soft bright fringe in the black immediately beside a white shape. The fringe is the halo. If the black away from any white shape is uneven, that is a different question and this pattern is not the tool for it.
- Center block: one white square on black, so you can watch the edge around a single bright object.
- Small highlights: short white bars, closer to subtitles or a small interface mark.
- Bright frame: a white border around a black center, so you can see whether glow washes inward.
- Size: small, medium, or large, about 9, 18, and 36 percent of the stage for the center block.
The page does not count dimming zones, measure the halo in millimeters, or decide that the display is broken. A dark screen with no bright shape is the black field on the Black Level Test.
How to use this blooming test
The stage opens with a white block in the center of a black field. Look at the black beside the block, not at the white itself. A halo is a soft brightening that clings to the shape and fades into the background. Switch among Center block, Small highlights, and Bright frame. The size menu changes that shape among small, medium, and large: about 9, 18, and 36 percent of the stage width for the center block. Small highlights are short white bars. The bright frame is a white border around a black center, so you can see whether glow stays on the border or washes inward.
Use Full screen, then Hide controls, before you decide what the black looks like. The buttons and the rest of this white page are bright, and on some displays they lighten black that sits nearby. Click the pattern or press Escape when you want the controls back. Watch from your normal seat, with browser zoom at 100 percent. If you compare a picture setting, change one control and return to the same pattern and size.
What a halo around a bright object can mean
Some LCD televisions and monitors dim the backlight in zones. A small white object can sit inside a zone that is larger than the object, so the black around it rises with that zone. The result is blooming: a patch of gray or color around credits, a mouse pointer, a subtitle, or a star on a night scene. The zone count is a hardware design this page cannot see. A stronger halo on the small highlights than on the large block is consistent with zones that are coarse relative to the mark, but it is still a visual impression, not a count of zones.
ITU-R BT.2100 specifies image parameters for high-dynamic-range television, including transfer functions meant to carry brighter highlights and darker shadows in one picture. That wider gap can make a bright object on black easier to notice, including any halo around it. This page does not generate a PQ or HLG signal, does not set a nit target, and does not claim HDR compliance. It draws a white CSS shape on a black CSS field so you can look for that halo on the display you are using right now.
How block size and pattern change the check
A large block fills more of a dimming zone, so the glow may look like a modest fringe rather than a blob. A row of small highlights is closer to subtitles or a bright user-interface mark. Step through small, medium, and large without changing the display, and write down which size makes the halo easiest to see. The bright frame checks a different edge: light leaking from a white border into a black middle. If the center of the frame looks lifted while the black far from the border looks darker, keep that observation with the frame pattern. Do not average it with the center-block result into one score.
Move your head slightly left and right. Some glow changes with viewing angle because the panel’s light path changes, not because the test shape changed. A halo that appears only at a steep angle is a different note from a halo you see straight on. Also glance at the corners of the full-screen black. Uneven brightness with no bright shape nearby is a flat-field question, better compared on the Gray Uniformity Test or the black field of the Black Level Test.
Blooming, backlight bleed, and clouding
These words get mixed together. Blooming, as used here, follows a bright object: move the idea of the object and the glow stays with it. Backlight bleed and clouding are often discussed as light that pools at edges or in patches even when the image is dark all over. A corner that glows during the black field, with no white shape on it, is not evidence of the same thing as a ring around the center block. Local dimming can also be turned down or off in a picture menu. If the halo shrinks when local dimming is reduced and the rest of the image gets brighter or flatter, you have learned how that setting trades black for halo. That is a preference, not an automatic fault.
OLED panels do not use a backlight zone in the same way. A bright shape can still look soft because of pixel response, image processing, or the way you are sitting. A single pixel that stays lit after the shape is gone belongs on the Dead Pixel Test. A moving white edge that leaves a trail is the subject of the Motion Blur Test. This page holds the shape still so the halo is not confused with motion smear.
Compare one display setting at a time
Local dimming, contrast, brightness, HDR picture mode, and game-mode processing can each change the halo. Pick the pattern where you saw it most clearly. Change one setting by one step. Hide the controls and look again for about ten seconds, which is long enough to let a dimming feature settle and short enough that your eyes are still adapted to the same room. Then put the setting back. A halo that only appears with local dimming on its highest step is useful information about that step. A halo that remains after dimming is off may be backlight bleed, viewing angle, or a reflection.
Room light matters. A lamp in the screen will hide a faint halo and can also create a bright patch that looks like glow. Turn the lamp off or change your seat so the reflection leaves the shape. Browser zoom and operating-system scaling change how large the CSS shape is in device pixels. Stay at 100 percent browser zoom unless you are deliberately comparing scaling. A second browser is a reasonable check if the fringe looks like a software shadow rather than a glow on the panel.
What this blooming test cannot measure
The page cannot count dimming zones, measure the width of a halo in millimeters, or report a contrast ratio beside the white shape. It cannot tell you whether a manufacturer’s zone specification is accurate. Eye adaptation, reflections, and viewing angle all change what a faint fringe looks like, so two viewings in different rooms can disagree. Use the three patterns as a repeatable way to look, keep the pattern name and size in your note, and compare like with like. A visible halo on a local-dimming display can be normal behavior of that design. It becomes a problem for you only when it distracts in the scenes you actually watch, which this still test pattern can suggest but cannot decide.
Frequently asked questions
What does this blooming test check?
It checks whether the black next to a bright shape turns lighter, which is the halo. You can compare a center block, a row of small highlights, and a bright frame, each at a small, medium, or large size. It does not count backlight zones.
What should a blooming test look like?
Look at the black immediately beside each white shape. A soft brightening that follows the shape is the halo this page is for. A perfectly hard edge is not guaranteed, and a faint fringe can come from the browser, the panel, or both.
Does a halo mean the display is broken?
No. Local dimming, a high backlight, and viewing angle can all create a glow around bright objects on black. Compare the same pattern after changing one setting, and compare a large block with the small highlights, before treating the picture as a defect.
Why do the page buttons make the black look lighter?
Bright controls can light up nearby backlight zones. Choose Full screen, then Hide controls, and judge the area around the test shape rather than the edge next to the buttons.