What Is FALD Blooming Or Halo Effect?

Answer:

On displays with Full-Array Local Dimming (FALD), blooming (also referred to as halo effect) occurs when the light that’s illuminating a small object bleeds into the surrounding dimmed zones.

Just how bad the blooming is depends on the number of dimming zones the monitor has and how demanding the displayed scene is.

Unlike OLED displays which are self-emissive, LED monitors and TVs rely on a backlight to produce the picture.

This means that LED-backlit displays cannot produce true blacks and that some light will always bleed/pass through the panel thus resulting in backlight bleeding or VA/IPS glow depending on the panel type.

In order to bring the image quality of LED displays closer to that of OLEDs, some manufacturers implement localized dimming in their monitors and TVs. While this technology does help with the picture quality, it’s not perfect.

What Is Local Dimming?

different local dimming types

Most LED displays use global dimming where the entire picture gets darker with dark scenes – or brighter with bright scenes. In short, there’s no localized dimming which is why you get such limited contrast ratio with this type of displays.

Next, there are edge-lit displays which have several dimming zones at either top/bottom or left/right side of the screen.

While these displays can increase the contrast ratio a bit, there won’t be any improvement in scenes in which there are a lot of dark and bright details close to each other due to the limited number of dimming zones.

In scenes where the contrasting elements appear far from each other, the picture quality won’t be ideal either as vertical or horizontal banding can occur. In other words, edge-lit local dimming is not very effective except in some rare scenes.

With full-array local dimming solutions, LEDs are placed across the entire screen behind the panel for a much better control of dimming zones according to the displayed content.

However, FALD displays are also considerably more expensive and bulkier in design.

edge lit vs full array local dimming

FALD: Pros and Cons

Besides the heftier design and price tag, FALD displays can also exhibit blooming in certain scenarios.

If you have a small bright object, such as a cursor, on a plain dark background, some light from the cursor will bleed into the surrounding dimmed zones and create the halo/bloom effect that will follow your cursor as you move it.

Of course, local dimming wasn’t designed for regular desktop use, so in video games and movies, this will be much less noticeable. You can simply disable local dimming when not watching videos or playing games.

Depending on the number and size of dimming zones, some blooming can also be visible in certain scenes in games and movies too – but in all except for the most extreme cases, it’ll be negligible.

The most popular gaming monitors with FALD solutions include the ASUS PG27UQ and the Acer Predator X35.

In the near future, manufacturers will turn to Mini LEDs which allow for additional dimming zones.

The PG27UQ with a 384-zone FALD solution, for instance, will be available as the PG27UQX with 576 Mini LED dimming zones which should reduce the amount of visible blooming by 33%!

While still not perfect, these FALD displays do offer the best HDR image quality possible on gaming monitors, at least until OLED and MicroLED gaming monitors become available.

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Rob Shafer
Rob Shafer

Rob is a software engineer with a Bachelor’s degree from the University of Denver. He now works full-time managing DisplayNinja while coding his own projects on the side.