What Is Local Dimming and Why Does It Matter for HDR?

2026-03-28

Quick Answer

LCD pixels cannot switch themselves off, so local dimming controls the backlight in independent zones to darken the parts of the image that should be black. The number and placement of those zones decides the quality: edge-lit panels have a few dozen and bloom badly, while full-array and Mini-LED designs run hundreds to thousands.

Why LCD needs local dimming

LCD panels cannot turn individual pixels off. They are lit by a backlight - usually an array of LEDs - and the liquid crystal layer modulates how much of that light passes through. Even a "black" pixel has some backlight shining through it, creating the glow you see in a darkened room.

In HDR content, a scene may have a bright star against a deep black sky. A standard LCD will light the entire panel at whatever brightness the star requires - washing out the blacks.

Local dimming solves this by controlling the backlight in zones independently. The zone behind the star is bright; the zone behind the black sky is dimmed or off.

Edge-lit vs. full-array local dimming

Edge-lit local dimming: LEDs are placed on the edges (top/bottom or all four sides). Light is directed inward with a light guide. Local dimming zones are very coarse - typically only 8–32 zones across a 27-inch panel. The effect is limited. You may see light blooming around a bright object into adjacent dark areas.

Full-array local dimming (FALD): LEDs are mounted directly behind the panel in a dense array. Each zone diameter is smaller. High-end monitors use 512, 1024, or even 2000+ zones. The more zones, the more precise the dimming - less halo, better black levels.

Mini-LED: Uses thousands of tiny LEDs behind the panel (Samsung, LG, ASUS), enabling hundreds to thousands of dimming zones. This is the technology that makes LCD competitive with OLED for contrast.

The blooming artifact

No zone-based local dimming is perfect. The zone around a bright object is lit, illuminating nearby pixels. On a 32-zone display, a white subtitle in a black letterbox can create a visible rectangle of light around it. This is called blooming or haloing.

The solution is more zones. At 2000+ zones, blooming becomes nearly invisible in practice.

OLED: pixel-level dimming

OLED sidesteps this entirely. Each OLED pixel is its own light source and can switch completely off. Contrast ratio is effectively infinite - a lit pixel next to a black pixel has no crosstalk. This is why OLED black levels look better than even the best local dimming LCD.

What to look for when buying

Check how many local dimming zones the monitor has. A "Full Array" monitor with 8 zones is barely better than edge-lit. Look for 500+ zones for quality HDR on LCD. For truly excellent dark scene performance, Mini-LED (1000+ zones) or OLED are the standards to compare against.

Frequently Asked Questions

What is blooming on a monitor?

Blooming, also called haloing, is the glow of light that spreads from a bright object into surrounding dark areas. It happens because a whole dimming zone has to light up for anything inside it, so on a 32-zone display a white subtitle in a black letterbox can produce a visible rectangle of light around it.

What is the difference between edge-lit and full-array local dimming?

Edge-lit places LEDs along the borders and directs light inward, giving very coarse control, typically only 8 to 32 zones across a 27 inch panel. Full-array mounts the LEDs directly behind the panel, so zones are smaller and far more numerous, with high-end monitors using 512, 1024 or more.

How many dimming zones is enough?

More zones mean smaller halos and better black levels. A few dozen zones produce obvious blooming, several hundred make it much harder to spot, and Mini-LED designs with thousands of zones are what allow LCD to compete with OLED on contrast.

Why does OLED not need local dimming?

Each OLED pixel emits its own light and can switch off completely, so black is genuinely black without any backlight to control. Local dimming exists purely to work around the fact that an LCD backlight shines through even a black pixel.

Should I turn local dimming on or off?

Leave it on for HDR content, where it is the whole point. On a panel with few zones you may prefer it off for desktop work and subtitled video, because the blooming around bright interface elements and text can be more distracting than the improved black level is worth.