Local dimming is a backlight technology in LCD displays that divides the screen’s LED backlight into separate zones, each controlled independently. Instead of lighting the entire screen at one uniform brightness, the display dims zones showing dark content while keeping bright zones fully lit. The result is deeper blacks, higher contrast, and better energy efficiency.
How Local Dimming Works
Every LCD screen needs a backlight because the liquid crystal layer doesn’t produce its own light. In a standard LCD without local dimming, that backlight stays at roughly the same brightness across the whole panel. Dark scenes in a movie still have light pushing through from behind, which makes blacks look more like dark gray.
Local dimming solves this by splitting the backlight into a grid of independently controlled zones. When the display detects that part of the image should be dark, it reduces or shuts off the LEDs in that zone. Bright areas of the image get full power. The display’s processor analyzes every frame in real time, deciding how much light each zone needs and applying pixel-level compensation to keep colors and details accurate in the transitions between bright and dim zones.
Full-Array vs. Edge-Lit Designs
Not all local dimming systems are built the same. The two main designs differ in where the LEDs sit physically behind (or around) the screen, and that placement has a big impact on performance.
Full-array local dimming (FALD) places LEDs in a grid across the entire back of the panel. Because every section of the screen has LEDs directly behind it, each zone can be controlled with precision. This is the higher-performing approach, and it’s what most mid-range and premium TVs use today.
Edge-lit local dimming positions LEDs only along the edges of the display, with the light directed inward through a light guide. Edge-lit TVs can create a rough local dimming effect by turning certain edge LEDs on or off, but the control is far less precise. You might notice uneven brightness or light spilling into areas that should be dark, especially in large dark scenes with a few bright highlights.
Why Zone Count Matters
The number of dimming zones is one of the biggest factors in how well local dimming performs. More zones means each zone covers a smaller area of the screen, so the display can be more surgical about where it dims and where it stays bright. A few years ago, 100 or so zones was typical. Today, several thousand zones is common in mid-range TVs thanks to advances in mini-LED backlighting.
Mini-LED technology shrinks each LED to a fraction of the size of traditional backlight LEDs. That lets manufacturers pack far more of them behind the panel. A 32-inch gaming monitor from BenQ, for example, uses 1,152 dimming zones to hit 1,000 nits of peak brightness. High-end TVs now push well beyond that. The smaller each zone, the tighter the control over where light appears on screen, and the less visible any dimming artifacts become.
Research from Texas Instruments illustrates the relationship between zone count and contrast. For an LCD panel with a native contrast ratio of 2,000:1, you’d need over 3,000 local dimming zones to eliminate visible halo artifacts and approach OLED-like black levels. A panel with a better native contrast ratio of 5,000:1 could achieve similar results with just 200 zones. In other words, zone count and panel quality work together.
Local Dimming and HDR
Local dimming is essential for HDR (high dynamic range) content. HDR video contains a much wider range of brightness levels than standard content, from deep shadows to intense highlights. A display needs to produce very bright whites and very dark blacks simultaneously to show that range properly, which is exactly what local dimming enables.
The VESA DisplayHDR certification system reflects this directly. At the DisplayHDR 1000 tier and above, two-dimensional local dimming is a requirement. Lower tiers can pass without it, but their black level performance suffers as a result. The certification also includes a subtitle flicker test, which checks whether the local dimming algorithm handles rapid brightness changes smoothly. This matters in real-world viewing: when bright subtitles pop on and off against a dark movie scene, a poorly tuned algorithm can cause visible brightness flickering around the text.
The Blooming Problem
The most common complaint about local dimming is blooming, sometimes called the halo effect. It happens when a small bright object on a dark background causes light to bleed into neighboring dimmed zones. Picture a white mouse cursor on a black screen: the zone behind the cursor lights up, but some of that light spills into the surrounding dark zones, creating a visible glow or halo around the cursor. Move the cursor and the halo follows.
Three things determine how noticeable blooming is. First, the number of dimming zones: more zones mean smaller halos because each lit zone covers less screen area. Second, the quality of the dimming algorithm, which decides how aggressively to dim surrounding zones and how to compensate at the pixel level. Third, the content itself. A single star on a black sky is a worst-case scenario for any local dimming system. A brightly lit sports broadcast with few dark areas won’t trigger noticeable blooming at all.
Unlike OLED and micro-LED displays, which control light at the individual pixel level (millions of independent zones, effectively), even the best LCD local dimming system is working with hundreds or thousands of zones for millions of pixels. Some light leakage is inherent to the technology. This is why OLED displays can produce perfect blacks in any scene, while LCD displays with local dimming get close but never fully eliminate backlight bleed.
How It Affects What You See
With local dimming turned on, the most obvious improvement is in dark scenes. Black bars on a letterboxed movie actually look black instead of glowing gray. Night scenes in games and films have more visible shadow detail because the contrast between lit and unlit parts of the image is dramatically higher. VESA’s testing shows that high-end local dimming displays can reach black levels as low as 0.05 nits while simultaneously displaying maximum white brightness, compared to edge-lit displays without effective dimming that sit around 0.4 nits or higher.
Energy efficiency is a secondary benefit. When large portions of the screen are dark, those zones draw less power. This is particularly noticeable on laptop displays, where dimming unused backlight zones can meaningfully extend battery life during movie playback or dark-themed app usage.
Most TVs and monitors let you adjust local dimming intensity in the settings menu, typically offering low, medium, and high options. Higher settings produce deeper blacks but can make blooming more visible in tough scenes. Lower settings reduce blooming but sacrifice some of the contrast improvement. The best setting depends on what you watch most and how much blooming bothers you. For movie watching in a dark room, higher settings generally look better. For desktop use with lots of bright UI elements on dark backgrounds, a lower setting can reduce distracting halos.