Have you ever noticed a bright, fuzzy glow around a light object on your TV screen when the rest of the image is dark? This is known as the local dimming halo effect, or blooming, and it’s a frustrating flaw that can diminish the quality of high-end displays. While local dimming is intended to boost contrast, this artifact can ruin the immersive experience.

Fortunately, modern display technology, pairing Chip on Board (COB) manufacturing with a sophisticated Multiplexing control method, delivers a powerful and cost-effective solution. This duo enables new displays to achieve incredibly precise local dimming, all but eliminating the halo effect and delivering unparalleled contrast.

What is Local Dimming and what is the “Halo Effect”?

Local dimming is a display feature designed to improve the contrast ratio of LED-backlit LCD screens, including televisions, monitors, and laptops. Instead of a single, always-on backlight, local dimming divides the backlight into a grid of zones. The display’s processor can then individually adjust the brightness of each zone to match the on-screen content.

• During a dark scene, the backlight zones behind dark areas of the image are dimmed or turned off, creating deeper, richer blacks.
• During a bright scene, the backlight zones are brightened to make highlights pop.

This dynamic process is what creates high dynamic range (HDR) and significantly improves the picture quality over standard LED displays.
The “halo effect” occurs when a bright object is displayed against a dark background. The object sits within a single local dimming zone, and the entire zone must be lit to illuminate it. This causes the light to “bleed” or “bloom” beyond the object’s edges, creating a distracting halo. The fewer the dimming zones a display has, the larger the area each zone must cover, which makes the halo effect more pronounced.

The Mini-LED Revolution: More Zones, Less Bloom

The solution to the halo effect is simple in principle: shrink the dimming zones. By using a much higher number of smaller LEDs, a display can have more, and therefore smaller, dimming zones. This is where Mini-LED technology comes into play. Mini-LEDs are smaller than traditional LEDs and are arranged in a dense grid behind the screen. This allows for:

• More precise control. The dimming zones become more granular, so the backlight can more accurately match the shape of the content.
• A higher number of zones. Where a traditional FALD (Full-Array Local Dimming) screen might have a few hundred zones, a Mini-LED screen can have thousands.

How Chip on Board (COB) takes Mini-LED to the next level

Mini-LED displays with traditional manufacturing methods already reduce the halo effect, but they don’t eliminate it entirely. This is where the integration of Chip on Board (COB) manufacturing offers the most advanced solution yet. In a COB backlight, bare LED chips are mounted directly onto a circuit board, eliminating the need for bulky packaging. This approach has several key benefits that directly address the limitations of older local dimming designs:

1. Dramatically higher LED density. COB allows manufacturers to pack far more tiny LEDs into a smaller space than other methods. This enables an unprecedented number of local dimming zones, some with tens of thousands of individual zones.
2. Smaller, more precise dimming zones. With more LEDs packed tightly together, the size of each dimming zone can be reduced to an absolute minimum. The smaller the zone, the less visible the halo becomes, as light is contained within a much more confined area.
3. Superior uniformity. COB backlights create a more uniform and consistent light output across the entire display. This smoother light distribution further minimizes the visual discrepancies that can contribute to blooming.

The challenge with a massive array of thousands of COB LED zones is control. It would be impractical and prohibitively expensive to run a separate wire to each zone. This is where multiplexing, also known as “time-division multiplexing,” comes in. Multiplexing is a technique that controls a large array of LEDs with far fewer connections or in simple words, controls a single LED zone with fewer driver ICs. Here’s how it works:

• Efficient Scans: The LED array is organized into a matrix of rows and columns. Instead of lighting all LEDs at once, specialized driver ICs activate one row at a time, cycling through them at extremely high speeds.
• High-Speed Control: During the brief moment a row is active, the driver sends the correct brightness information to each LED in that row. The scan then quickly moves to the next row, repeating the process.
• The Illusion of Light: This scanning happens so fast—hundreds of times per second—that your eye’s persistence of vision perceives a perfectly solid, continuously lit image. This process dramatically reduces the number of physical wiring connections needed, making the high-density COB array feasible and cost-effective.

Why COB with Multiplexing beats Standard Local Dimming?

Feature	COB with Multiplexing	Standard Full-Array Local Dimming
Zone Control	Thousands of zones are possible with simplified wiring, enabling a superior level of detail.	Often limited to dozens or hundreds of zones due to wiring limitations, leading to less precise dimming.
Halo Effect	Minimized due to the dense, uniform light output of the COB array and smaller dimming zones.	More pronounced “halo” or “bloom” effect is common due to larger dimming zones and more light leakage.
Manufacturing Cost	Reduces costs by using fewer components (no individual LED packaging) and simplified control wiring.	Can be more expensive due to the need for individual LED packages and more complex wiring.
Space Efficiency	Allows for more compact and thinner display designs by directly mounting LED chips on the PCB.	Requires more space for individual LED packages and the associated wiring, leading to thicker chassis.

The end of the halo effect?

For consumers, the difference is clear. While a standard local dimming screen might produce a noticeable halo around subtitles or a moon in a night sky, a premium Mini-LED display with a COB backlight will show a crisp image with deep, inky blacks and brilliant whites right next to each other, just like an OLED.

While no LCD-based technology can perfectly replicate the per-pixel dimming of an OLED, the combination of our local dimming, Chip on Board manufacturing, and multiplexing in modern Mini-LED displays gets impressively close. If you’re tired of the “halo effect” distracting from your favorite movies and shows, seeking out a Mini-LED display that leverages COB technology is your best bet for a truly high-contrast, immersive viewing experience.