What Is Local Dimming? FALD, Mini LED, and Edge-Lit Explained

Local dimming is the technology that allows LCD displays to produce deep blacks and bright highlights simultaneously — the contrast effect that makes HDR look impressive. Without local dimming, LCD displays have a single backlight that's either on or off, producing grayish blacks in dark scenes. With local dimming, the backlight is divided into zones that can be independently dimmed or turned off, allowing dark areas to be truly dark while bright areas stay bright.

The quality of local dimming determines whether an LCD produces good HDR or mediocre HDR. A display with 8 dimming zones (edge-lit) produces barely visible HDR with severe blooming. A display with 1000+ dimming zones (Mini LED) produces excellent HDR with minimal blooming. The number of zones is the single most important spec for LCD HDR performance — more important than peak brightness or color gamut.

This guide explains the three types of local dimming (edge-lit, FALD, Mini LED), how they differ in performance, what to look for when shopping for an HDR display, and how to test your display's local dimming quality. By the end, you'll understand why some HDR monitors look dramatically better than others despite similar brightness specs.

Blooming (also called halo) is the visible glow around bright objects on dark backgrounds, caused by local dimming zones being larger than individual pixels. When one pixel in a zone is bright, the entire zone lights up, contaminating the surrounding black area with unwanted light. The size and intensity of the halo is proportional to the zone size — fewer, larger zones produce larger, more visible halos.

Edge-lit displays with 8–16 zones produce severe blooming — bright objects (like subtitles, stars, or a cursor on black) create large diffuse halos that can extend inches into the surrounding black area. This ruins dark scene viewing and is the primary reason edge-lit LCDs produce poor HDR. The blooming is most visible in dark rooms with high-contrast content (starfields, credit rolls, horror movies).

Mini LED with 1000+ zones reduces blooming to small, tight halos that are barely visible in normal content. Premium Mini LED with 2000+ zones produces blooming that's only visible on test patterns, not in real content. OLED eliminates blooming entirely — each pixel is its own light source, so a bright pixel doesn't affect its neighbors. For more on blooming, see our blooming test and the Mini LED vs OLED guide.

Most displays with local dimming offer multiple settings (Off, Low, Medium, High). Each setting trades off brightness versus blooming differently. The right setting depends on your content and viewing environment.

Off: No local dimming. The backlight is uniformly lit. Produces grayish blacks (no contrast benefit) but zero blooming. Best for SDR content in bright rooms where blooming would be distracting and blacks don't need to be deep.

Low/Medium: Conservative local dimming. Produces moderate contrast improvement with minimal blooming. Best for SDR content in moderate lighting and HDR content in bright rooms where some blooming is acceptable.

High: Aggressive local dimming. Produces maximum contrast (deepest blacks, brightest highlights) with more visible blooming. Best for HDR content in dark rooms where contrast matters most and some blooming is acceptable. This is the setting most reviews test for HDR performance.

For HDR movies in a dark room, use High. For SDR content in a bright room, use Low or Off. For mixed use, Medium is a good compromise. Experiment with each setting on different content to find what works best for your viewing environment. For more on HDR setup, see our HDR test and the black level test.