TVs
How to determine whether a TV's local dimming implementation improves perceived contrast without producing distracting halo artifacts.
This guide explains practical methods to assess local dimming performance for brighter whites, deeper blacks, and minimal halo, using measurable cues, viewing environments, and consumer-tested benchmarks.
Published by
Nathan Turner
July 24, 2025 - 3 min Read
Local dimming is designed to boost contrast by brightening dark areas without washing out bright content. However, not all implementations deliver a clean improvement; some may introduce halos around bright objects on dark backgrounds. The key is to separate true luminescence gains from geometric or processing side effects. Start by understanding your panel type, whether it uses a full-array backlight with variable zones or a direct-lit array. Then evaluate the firmware’s decision logic at different brightness levels, because halo tendencies often worsen in mid-tone scenes where edges and textures compete for boundary definition. Finally, consider upscaling behavior, HDR handling, and ambient light management, since these factors influence how local dimming interacts with perceived contrast.
A practical assessment involves a controlled scene with a bright object placed against a dark field and then reversed. Capture quick observations by eye first, noting whether dark edges appear to glow around bright shapes. Use a consistent brightness setting across test content to prevent misinterpretation. If halos surface, observe their thickness, intensity, and color shift. Some displays hide halos at very low or very high luminance, so test across a spectrum of scenes—from star-filled skies to moonlit windows, and from sharp text to soft gradients. Comparing multiple sources helps distinguish manufacturing quirks from universal strengths or weaknesses in the dimming algorithm.
Evaluating halo behavior across real-world content and scene variation.
Start with a high-contrast checkerboard pattern and a solid black field to stress boundary clarity. This combination highlights how local dimming maps zones and handles transitions. Note whether the bright interstitials bleed into adjacent darkness, creating a noticeable halo that doesn’t align with actual light falloff. Documenting these artifacts in both animated and still frames helps reveal dynamic processing issues. Additionally, watch for edge artifacts around letterforms in subtitles or UI elements, where halos can degrade legibility more than in wide ambient scenes. A well-behaved system should minimize both visible halo and shimmering under slight lighting changes.
Move to a grayscale sweep that moves from near-black through mid-tones to bright whites. Observe where the image’s contrast appears strongest and where it seems softened by the dimming algorithm. Halo tendencies often become apparent as light bleeds outward from bright contours into surrounding dark zones, especially along curved shapes and fine textures. Compare the same content on another display with a known, clean local dimming performance to establish a reference point. Pay attention to how quickly the system transitions between dimming states as scenes change; abrupt transitions can resemble halo-like artifacts even when the boundary handling is otherwise solid.
How to separate true contrast boost from distracting halo artifacts.
Real-world footage, such as nighttime cityscapes or starry skies, exposes how a dimming system responds to complex brightness gradients. A genuine improvement in perceived contrast should render distant lights with more depth without creating a circular glow around illuminated bulbs. Also watch for “bloom” in white areas where the highlight radiates beyond its actual boundary. When testing, switch between P and S modes if your set offers them; some implementations optimize for cinema-like contrast, while others prioritize energy efficiency, which can alter halo visibility. The goal is a balanced, natural look that preserves texture details in shadows and avoids unintended halo rings.
Commercial reviews sometimes cite peak luminance and uniformity without addressing halo quality directly. To fill that gap, perform side-by-side comparisons with the same content under identical settings on two TVs or two input sources. Use a neutral color demo and a fast-moving scene to reveal dynamic dimming behavior. If halos appear inconsistently with motion, note whether the artifact stabilizes or intensifies as motion continues. The presence of motion-induced halos can be especially distracting in sports or action movies. A careful observer should differentiate corner-case halo moments from persistent boundaries that undermine overall contrast perception.
Practical buying guidance for choosing better local dimming performance.
A meaningful test isolates local dimming from other processing stages like tone mapping and edge sharpening. Disable extra processing where possible and reuse the same reference content to prevent content bias. Then re-enable processing in measured steps to observe incremental changes. When you see improved shadow detail but new halos around bright shapes, assess whether the gain justifies the artifact. Some viewers tolerate small halos if overall scene depth substantially improves, while others find halos ruin the immersion. The best-performing sets meet in the middle, delivering more depth with minimal halo presence across diverse lighting.
Finally, consider the room and viewing distance. In bright rooms, halos are more noticeable because bright edges stand out against ambient reflections. Conversely, a dim, controlled space reduces visual noise and halo perception, enabling a more accurate judgment of local dimming quality. Use calibrated viewing conditions or near-reference brightness with consistent color temperatures to avoid misinterpretation. Remember that some halo artifacts are more visible on certain screen finishes or with specific panel coatings, so account for hardware variability as you compare models. The outcome should feel natural rather than artificially enhanced.
Final steps to verify perceived contrast without halo distractions.
When shopping, seek displays that provide explicit halo performance measurements in official specs or reviews. Look for user-controlled dimming zone counts, variable backlight depth, and independent validation of perceived contrast improvements. A higher zone count usually enables finer gradations and tighter control, reducing halo risk, but the trade-off is potential processing artifacts if the firmware isn’t optimized. Favor models with robust motion handling and consistent HDR tone mapping, as these elements influence halo visibility in dynamic content. In-store demonstrations should include dark scenes with bright highlights to give a live sense of halo behavior; if halos are obvious in person, consider another option.
Also factor in firmware support and future-proofing. Some televisions receive periodic updates that refine local dimming behavior, suppress halo artifacts, or improve color accuracy in HDR. A device with a track record of meaningful software improvements can yield a longer-term benefit than a mere hardware spec bump. Additionally, read independent test results noting halo stability across different input resolutions and HDMI versions. If possible, request a hands-on test at a retailer with representative content, ensuring you observe performance across multiple brightness settings and viewing angles for a complete assessment.
Before committing to a purchase, reconstruct the test routine with content you actually watch and in the lighting you normally use. This personalization helps reveal whether perceived improvements translate to your everyday experience. Document consistency across scenes, such as sports, films, and animated content, where halos can differ by motion and edge complexity. If you consistently notice halos around bright elements in your usual viewing, seek models known for better boundary handling or with firmware options to tune the behavior. The aim is a natural, immersive image where increased depth does not come at the cost of distracting outlines.
In summary, evaluating local dimming requires a systematic approach: controlled tests, real-world content, and a careful eye for halo artifacts across various brightness and motion scenarios. Knowledge of panel design, firmware behavior, and room conditions helps you separate actual contrast gains from processing quirks. By comparing multiple displays under identical test conditions and seeking reliable, user-adjustable controls, you can choose a TV that delivers meaningful depth without the distraction of halos. The result is a viewing experience that feels true-to-life, steady, and comfortable across hours of entertainment.
