BlackScreen.liveLocal Dimming Zones Explained
Local dimming is the technology that separates genuine HDR monitors from displays that merely carry an HDR label. Understanding how local dimming works, what the different implementations offer, and how to evaluate performance helps you make informed decisions when purchasing an HDR monitor.
LCD panels cannot achieve true black because the backlight is always on. Local dimming addresses this limitation by dividing the backlight into independently controllable zones—dimming zones that display dark content while keeping zones with bright content at full brightness. The result is dramatically improved contrast ratios compared to global dimming.
1. Edge-Lit Local Dimming
Edge-lit displays place LEDs along the edges of the panel (typically top and bottom, or all four sides). Light is distributed across the panel through a light guide plate. Local dimming in edge-lit displays controls groups of edge LEDs.
Limitations
Edge-lit local dimming has severe limitations because the LEDs are far from the center of the panel. Dimming one edge affects a large area of the display, creating visible "blooming" (bright halos around bright objects on dark backgrounds). Most edge-lit "local dimming" implementations have only 8-32 zones—far too few for effective HDR.
Edge-lit local dimming is primarily a marketing feature on budget monitors. It provides minimal real-world benefit and can actually make HDR content look worse due to aggressive blooming artifacts.
2. Direct-Lit Local Dimming
Direct-lit displays place LEDs directly behind the panel in a grid pattern. This allows more precise control of different screen regions. Typical direct-lit monitors have 32-512 dimming zones.
Direct-lit local dimming provides meaningful contrast improvement over edge-lit, but blooming is still visible when bright objects appear on dark backgrounds. The zone size (panel area divided by zone count) determines how precisely the backlight can be controlled.
3. Full-Array Local Dimming (FALD)
FALD uses a dense grid of LEDs directly behind the panel with hundreds to thousands of independently controllable zones. This is the technology used in premium LCD monitors and TVs.
Zone Count and Performance
Zone count is the primary determinant of FALD performance:
- 32-128 zones: Basic FALD. Visible blooming on high-contrast content. Meaningful improvement over edge-lit.
- 256-512 zones: Good FALD. Blooming reduced to acceptable levels for most content. Suitable for HDR600 certification.
- 512-2048 zones: Excellent FALD. Minimal blooming. Suitable for HDR1000 certification. Samsung Neo G8 uses 2048 zones.
- 2048+ zones: Premium FALD. Near-OLED contrast in many scenarios. Apple Pro Display XDR uses 576 zones but with very small LEDs.
4. Mini-LED Local Dimming
Mini-LED technology uses LEDs that are 100-200 micrometers in size (compared to 1-3mm for standard LEDs). This allows dramatically more LEDs to be packed into the same space, enabling thousands of dimming zones.
Mini-LED Advantages
- Thousands of dimming zones (Samsung Neo G8: 2048, Apple Pro Display XDR: 576 with very small zones)
- Higher peak brightness than standard FALD (1000-2000+ nits)
- Faster dimming response than standard LEDs
- Thinner panel construction possible
Mini-LED Limitations
- Blooming still occurs, though much less than standard FALD
- Higher cost than standard FALD
- Cannot match OLED's per-pixel control (each zone still covers many pixels)
5. Local Dimming vs. OLED
Even the best Mini-LED local dimming cannot match OLED's per-pixel control. OLED turns off individual pixels for black, while local dimming controls zones of thousands of pixels. The practical difference:
- A star field (many small bright points on black) looks perfect on OLED but shows blooming halos on even the best Mini-LED
- Large dark areas with bright highlights look nearly identical on premium Mini-LED and OLED
- Mini-LED can achieve higher peak brightness than OLED, which matters for HDR highlights
6. Testing Local Dimming Performance
Use our black screen test to evaluate your monitor's local dimming performance. Display a pure black screen and look for any visible zones that are brighter than others—this indicates poor local dimming calibration. For HDR testing, use our monitor test with HDR enabled.
Sources & Further Reading
Testing Local Dimming Performance
Local dimming performance is best evaluated with real-world content rather than synthetic test patterns. A well-implemented local dimming system should: maintain deep blacks in dark areas while displaying bright highlights, minimize blooming around bright objects on dark backgrounds, and respond quickly to scene changes without visible pumping or flickering.
Common local dimming artifacts to watch for: blooming (bright halo around objects on dark backgrounds), black crush (shadow detail lost in dark areas), and pumping (visible brightness changes when scene content changes). These artifacts are more pronounced with fewer dimming zones and less sophisticated dimming algorithms.
Use our black screen test to evaluate local dimming uniformity. A monitor with good local dimming should display near-perfect black across the entire screen. Our monitor test includes tests specifically designed to reveal local dimming artifacts.
Local Dimming Settings
Most monitors with local dimming offer multiple settings (Off, Low, Medium, High). Higher settings provide better contrast but more aggressive dimming that can cause more visible artifacts. For SDR content, Low or Medium settings often provide the best balance. For HDR content, High settings maximize the HDR effect. Disable local dimming entirely for color-critical work — it can affect color accuracy in bright areas.
The future of local dimming is moving toward higher zone counts and more sophisticated algorithms. Mini-LED technology enables thousands of dimming zones in a standard monitor form factor, approaching OLED's per-pixel control. As manufacturing costs decrease, high-zone-count local dimming will become standard in mid-range monitors, significantly improving HDR performance across the market.
Key Takeaways
Local dimming dramatically improves HDR performance by allowing selective backlight control. More zones means better performance with less blooming. Full-array local dimming outperforms edge-lit implementations. OLED's per-pixel dimming represents the ultimate implementation. When evaluating local dimming, test with real-world content and look for blooming, black crush, and pumping artifacts.
Frequently Asked Questions
How many local dimming zones do I need?
More zones generally means better HDR performance with less blooming. Entry-level monitors have 8-32 zones (minimal benefit). Mid-range have 100-500 zones (noticeable improvement). Premium monitors have 1000+ zones (near-OLED quality). OLED has per-pixel dimming — effectively infinite zones.
What is blooming in local dimming?
Blooming occurs when a bright object causes nearby dark areas to lighten because they share a dimming zone. A white subtitle on a black background will cause a visible halo around the text. More dimming zones reduce blooming by allowing finer control over which areas are brightened.
Is full-array local dimming better than edge-lit?
Yes, significantly. Full-array local dimming places LEDs behind the entire panel, allowing precise control over brightness in any area. Edge-lit local dimming uses LEDs along the edges, which limits control to horizontal or vertical bands. Full-array is required for meaningful HDR performance.