Answer:
On displays with full-array local dimming (FALD), blooming (also known as the halo effect) occurs when light from a bright object bleeds into surrounding dimmed zones.
The severity of blooming depends on the number of dimming zones, the quality of the local dimming algorithm and the complexity of the scene being displayed.
Unlike self-emissive OLED displays, LED LCDs rely on a backlight to create the image.
This means that LED-backlit displays cannot produce true blacks, as some light will always pass through the panel, which results in backlight bleeding.
To bring the image quality of LED LCDs closer to that of OLED displays, some manufacturers implement local dimming in their monitors and TVs. While this technology does help with the picture quality, it’s not perfect.
What Is Local Dimming?
Most LED displays use global dimming, in which case the entire picture gets darker with dark scenes and brighter with bright scenes. In short, there’s no localized dimming, which is why you get such a limited contrast ratio with this type of display.
Next, there are edge-lit displays, which use several dimming zones located along the top and bottom or the left and right edges of the screen.
While these displays can slightly improve contrast, they offer little benefit in scenes with both dark and bright details close together 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 much better control of dimming zones according to the displayed content.
FALD: Pros and Cons
FALD displays can 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 – but in all except for the most extreme cases (night sky with stars, fireworks, etc.), it’ll be negligible. As for those demanding scenes, some users find them tolerable, while others find them too distracting.
The higher the zone count, the better. The local dimming algorithm is also important and varies from manufacturer to manufacturer – some focus on minimizing blooming (at the cost of maximum brightness), others will allow for higher brightness even if it means that there’s more blooming. On some displays, you can manually adjust the intensity of local dimming via a few different presets.
OLED displays don’t suffer from blooming, glowing, backlight bleeding and similar visual artifacts, so some users prefer them. The main drawbacks of OLED displays are the risk of permanent image burn-in and their lower sustained brightness in scenes with large bright areas compared to mini-LED displays.
In the video above, you can see how the BenQ EX321UX 32″ 4K 144Hz IPS monitor with an 1152-zone mini LED FALD backlight compares to the MSI MPG 321CURX with a QD-OLED panel.
For a more detailed comparison between different HDR displays, check out our W-OLED vs QD-OLED vs mini LED article.
