Local dimming zones are independent segments of a display backlight that can dim or brighten separately. This technology allows liquid crystal displays to shut off light in dark areas of an image while keeping bright areas illuminated, significantly improving the contrast ratio and delivering deeper black levels.
LCD panels cannot block 100% of the light from their backlight, often causing dark scenes to look gray or washed out. Local dimming zones solve this problem by dividing the background light into a grid of controlled sections. By dynamically adjusting the brightness of each zone based on the video content, displays can achieve truer blacks, brighter highlights, and a more realistic high dynamic range experience. This technology is widely used in modern televisions, gaming monitors, and high-end laptops.
Local dimming zones improve the contrast ratio of LCD screens by selectively dimming the backlight.
Higher zone counts generally result in better picture quality, finer control, and fewer visual artifacts.
This technology bridges the performance gap between traditional edge-lit LCDs and self-emissive OLED displays.
Common implementations include Edge-lit, Direct-lit, and Full-Array Local Dimming, with Mini-LED representing the cutting edge.
A prominent artifact of local dimming is blooming, where light leaks from a bright object into surrounding dark zones.
Traditional LCD screens use a uniform backlight that stays completely on, relying on liquid crystals to block light for dark scenes. Because liquid crystals are imperfect light blockers, some light always leaks through.
Local dimming zones change this process through a combination of hardware and software:
Analysis: The display processor analyzes the incoming video signal frame by frame to identify bright and dark areas.
Zonal Control: The processor sends instructions to the backlight grid, dimming the LEDs behind dark parts of the image and brightening LEDs behind vibrant elements.
Result: The user sees deep blacks right next to bright highlights, which drastically increases the perceived contrast.
The effectiveness of local dimming depends on how the LEDs are arranged and the number of zones available.
LEDs are placed only along the borders of the screen. The zones are arranged in long vertical or horizontal strips. This is the least effective type because dimming a specific spot requires dimming an entire column or row, often leading to large bands of visible light.
LEDs are placed directly behind the entire LCD panel in a grid format. This allows for precise control because zones are square shapes distributed uniformly across the screen. FALD displays typically offer dozens to hundreds of zones.
An advanced evolution of FALD that uses thousands of microscopic LEDs. Because the light sources are vastly smaller, manufacturers can pack thousands of individual dimming zones into a single screen. This configuration offers the closest performance to OLED by significantly reducing light leakage.
Zone Count: The total number of independently controlled backlight sections. Higher counts allow for precise light management.
Response Time: How quickly the zones can change brightness to match fast-moving on-screen objects. Slow zone response causes trailing shadows or delayed brightness.
Peak Brightness: Measured in nits, this dictates how bright a zone can flash during HDR playback, contrasting against dimmed sections.
Superior Contrast: Delivers deeper black levels that resemble self-emissive displays.
Enhanced HDR Performance: Allows highlights like explosions or sunlight to pop without washing out the entire scene.
Energy Efficiency: Lowers power consumption by dimming or turning off LEDs in dark scenes.
Blooming Effect: Also known as haloing, this occurs when a small bright object passes through a dark zone, causing light to bleed into the dark surroundings.
Black Crushing: Aggressive dimming algorithms may accidentally hide subtle details in dark areas, like shadows or clothing textures.
Added Cost and Thickness: Requires complex processing chips and more physical space, making displays thicker and more expensive.
| Technology Feature | Edge-Lit Local Dimming | Full-Array Local Dimming (FALD) | Mini-LED Local Dimming | OLED (Alternative) |
|---|---|---|---|---|
| Zone Count | Low (typically 8–24) | Medium (typically 50–500) | High (1,000–5,000+) | Infinite (Per-pixel dimming) |
| Contrast Ratio | Moderate | High | Very High | Infinite |
| Blooming Artifacts | High (Visible bands) | Medium (Halos around objects) | Minimal | None |
| Peak Brightness | Medium | High | Extremely High | Medium to High |
| Panel Thickness | Ultra-Thin | Thick | Medium | Ultra-Thin |
While zone count matters, the dimming algorithm is equally vital. A screen with fewer zones and an excellent algorithm can outperform a high-zone screen with slow, poorly optimized software that creates distracting light delays.
Local dimming significantly improves LCD contrast, but it does not make it self-emissive. OLED handles brightness at the individual pixel level (over 8 million zones on a 4K screen), whereas local dimming still groups thousands of pixels into a single backlight zone.
Backlight: The primary light source situated behind an LCD panel to make the image visible.
Blooming: The unwanted halo of light that appears around bright objects on a dark background.
Contrast Ratio: The measurement of the difference between the brightest whites and the darkest blacks a display can produce.
Mini-LED: A display technology using miniaturized backlighting diodes to greatly multiply local dimming zones.
OLED: Organic Light Emitting Diode, a display tech where every individual pixel creates its own light, eliminating the need for dimming zones.