Blooming & Local Dimming Test
See how much light spills around bright objects on a dark background. The size of that halo tells you how coarse your local dimming zones are, and OLED should show none at all.
The cleanest way to judge halo size against zone count
How to read this
- OLED: no halo at all. Each pixel emits its own light, so black next to white stays black.
- Mini-LED with many zones: a small tight glow, usually only visible in a fully dark room.
- Edge-lit LCD: a large obvious halo, sometimes a full bright band across the screen.
- Watch the moving cursor scene for pumping: zones brightening and dimming a beat behind the object is a dimming algorithm that cannot keep up.
Testing guide
How to test blooming and local dimming
An LCD backlight is divided into dimming zones that are far larger than a single pixel. When a small bright object sits on black, the whole zone behind it has to light up, and the excess light spills outward as a halo. How big that halo is tells you how many zones the panel really has.
Best for
- Judging local dimming quality before buying an HDR monitor or TV.
- Understanding why subtitles and bright UI elements glow in dark scenes.
- Comparing a Mini-LED panel against an OLED in the same room.
How to run the test
- 1Turn the room lights off, since blooming is only visible against genuinely dark surroundings.
- 2Start with the single bright dot and note how far the glow extends around it.
- 3Switch to the subtitle scene, which is where most people first notice blooming in real content.
- 4Watch the moving cursor scene to see whether the dimming algorithm keeps up or lags behind.
How to read the result
No halo at all means an OLED or another per-pixel emissive panel.
A small tight glow visible only in a dark room indicates a dense Mini-LED zone array.
A large halo, or a bright band spanning the screen, indicates edge-lit dimming with very few zones.
Zones visibly brightening and dimming behind a moving object is dimming lag, sometimes called pumping.
Related tools and guides
Frequently asked questions
What is blooming on a display?
Blooming, also called haloing, is the glow of light spreading from a bright object into the dark area around it. It happens because the backlight zone behind that object is much larger than the object itself, so the whole zone lights up and the surplus light bleeds outward.
Why does OLED have no blooming?
Every OLED pixel generates its own light and can switch off completely, so there is no shared backlight zone to spill from. A white pixel can sit directly next to a black pixel with no light crossing between them.
How many dimming zones do I need to avoid blooming?
There is no threshold that removes it entirely on an LCD, only diminishing visibility. A few dozen zones produce obvious halos, several hundred make them subtle, and Mini-LED panels with a thousand or more make blooming hard to spot outside deliberate test patterns.
Should I turn local dimming off?
For HDR content, no, it is what makes HDR work. On a panel with few zones you may prefer it off for desktop work and subtitled video, where the halos around bright text can be more distracting than the improved black level is worth.
What is dimming lag or pumping?
It is when zones brighten and dim a fraction of a second behind the content, so a moving bright object drags a visible glow behind it or the background pulses. It indicates a dimming algorithm that cannot react fast enough, and it is more distracting than static blooming.