Local Dimming and HDR: How Backlight Technology Affects Image Quality

Local dimming is a backlight technology that improves contrast and HDR performance by independently controlling zones of LEDs. This article explains how different local dimming implementations impact image quality, with practical advice for buyers in Singapore.

When you shop for a monitor in Singapore, you will encounter terms like local dimming and HDR on product pages and in reviews. These features are closely linked because the quality of HDR depends largely on how well a display can produce bright highlights and deep blacks simultaneously. Local dimming is the backlight technology that makes that possible on LCD panels. Without it, an LCD monitor cannot achieve the contrast required for convincing HDR.

This article explains how local dimming works, how it affects image quality, and what you should look for when choosing a monitor. We focus on concrete specifications, real-world performance, and the trade-offs that matter in Singapore’s market. For a broader overview of monitor selection, see the complete guide to choosing a monitor in Singapore.

What Is Local Dimming?

Local dimming is a backlight control technique used in LCD monitors and TVs. In a standard LCD panel, the backlight is either fully on or fully off across the entire screen. That means even when a dark scene is displayed, the backlight still emits light, which leaks through the liquid crystal layer and raises black levels. The result is a washed-out, greyish black.

Local dimming divides the backlight into zones. Each zone can be dimmed or brightened independently. When a part of the image is dark, the corresponding zone dims or turns off, allowing that region to appear truly black. When a part is bright, the zone stays at full intensity. This dynamic control dramatically improves contrast ratio and makes HDR content look more lifelike.

There are two main types of local dimming:

Full-array local dimming (FALD): LEDs are placed in a grid behind the entire screen. Each LED or group of LEDs forms a zone. FALD offers the best control because zones can be arranged in many rows and columns.
Edge-lit local dimming: LEDs are placed only along the edges of the screen (top, bottom, left, right). Zones are long vertical or horizontal strips. This design is cheaper and thinner but provides far less precise dimming.

In Singapore, most consumer monitors use edge-lit local dimming or no dimming at all. FALD is typically found on higher-end displays from brands like Dell, ASUS, and LG, often at prices above S$1,200. For example, the Dell U3223QE uses edge-lit dimming, while the ASUS ProArt PA32UCX-K uses a 576-zone FALD backlight and costs around S$4,000 at retailers like Sim Lim Square or online at Lazada.

How Local Dimming Affects Contrast and Black Levels

Contrast ratio is the difference between the brightest white and the darkest black a display can produce. A standard LCD without local dimming typically has a static contrast ratio of about 1000:1. With local dimming, the dynamic contrast ratio can exceed 1,000,000:1 because black areas can be made nearly black.

However, the number of zones matters. More zones allow finer control. A monitor with 8 edge-lit zones cannot dim a small dark object in the centre of the screen without also dimming the bright areas in the same strip. This causes blooming, a halo of light around bright objects on a dark background. Blooming is the most visible drawback of edge-lit local dimming.

FALD monitors with 384 or more zones can largely eliminate blooming. For instance, the LG 32GQ950-B has 32 edge-lit zones and shows noticeable blooming in HDR. In contrast, the ASUS ROG Swift PG32UQX has 1152 FALD zones and produces almost no visible blooming, but it costs about S$3,500 in Singapore.

For HDR, the key metric is peak luminance measured in nits. The VESA DisplayHDR standard defines tiers: DisplayHDR 400 (400 nits), DisplayHDR 600 (600 nits), and DisplayHDR 1000 (1000 nits). Local dimming is required to achieve DisplayHDR 600 or higher because the display must sustain high brightness in small areas while keeping the rest dark. Without local dimming, a monitor cannot pass the DisplayHDR 600 test.

In practice, a monitor with DisplayHDR 600 and decent local dimming will look noticeably better than one with DisplayHDR 400 and no dimming. The difference is especially clear in games and movies with high-contrast scenes, such as a starry sky or an explosion in a dark room.

Local Dimming and HDR: The Relationship

HDR (High Dynamic Range) content is mastered to a wider luminance range than standard SDR. An HDR signal tells the display to produce specific brightness levels for each pixel. An LCD panel can only achieve those levels if the backlight can dim and brighten in sync with the content. Local dimming is the mechanism that makes this possible.

Without local dimming, an LCD monitor that claims HDR support is essentially accepting an HDR signal but mapping it to the display’s limited contrast. This is often called HDR passthrough or fake HDR. The image may look slightly better than SDR due to tone mapping, but it will lack the punch and depth of true HDR.

For a monitor to deliver a convincing HDR experience, it needs:

A high peak brightness (at least 600 nits, preferably 1000 nits or more)
Local dimming with enough zones to minimise blooming
Wide colour gamut covering at least DCI-P3 90% (see colour gamut explained)
Good tone mapping to preserve highlight detail

Many monitors sold in Singapore as “HDR-ready” or “HDR10 compatible” lack local dimming and have peak brightness below 400 nits. These should be treated as SDR monitors that can accept an HDR signal, not as true HDR displays. For a deeper look at marketing claims, read HDR claims: what they mean.

OLED monitors, by contrast, do not need local dimming because each pixel emits its own light and can turn off completely. That gives OLEDs infinite contrast and perfect black levels. However, OLEDs have other trade-offs, such as burn-in risk and lower peak brightness in full-screen white. For a comparison of panel types, see IPS vs VA vs TN vs OLED.

Edge-Lit vs Full-Array: Real-World Performance

To understand how local dimming performs in practice, it helps to look at specific monitors available in Singapore.

Edge-lit local dimming examples

Many monitors in the S$500, S$1,000 range use edge-lit dimming with 8 to 32 zones. For instance:

Dell S2722QC (S$599 at Dell Official Store): 27-inch 4K IPS, edge-lit, 8 zones. HDR 400. In a dark room, you will see blooming around the cursor and bright subtitles.
LG 27UK850-W (S$699 at Courts): 27-inch 4K IPS, edge-lit, 12 zones. HDR 400. Similar blooming behaviour.
ASUS ProArt PA279CV (S$749 at Sim Lim Square): 27-inch 4K IPS, edge-lit, 8 zones. HDR 400. Suitable for photo editing in SDR but not for HDR.

These monitors are fine for SDR work and casual HDR viewing, but they will not deliver the immersive HDR experience that high-end TVs or OLEDs provide.

Full-array local dimming examples

FALD monitors are more expensive but offer much better HDR:

ASUS ProArt PA32UCX-K (S$3,999 at Lazada): 32-inch 4K IPS, 576-zone FALD, 1200 nits peak. DisplayHDR 1000. Excellent for professional HDR video editing.
ASUS ROG Swift PG32UQX (S$3,499 at Sim Lim Square): 32-inch 4K IPS, 1152-zone FALD, 1400 nits peak. DisplayHDR 1400. One of the best HDR gaming monitors.
Samsung Odyssey Neo G7 (S$1,499 at Samsung Online Store): 32-inch 4K VA, 1196-zone FALD, 1000 nits peak. DisplayHDR 1000. VA panel gives deeper native blacks.

The Samsung Neo G7 uses a VA panel, which has a higher native contrast ratio (around 3000:1) than IPS (1000:1). That means even without local dimming, VA panels show better blacks. With local dimming, the combination can be very effective. However, VA panels have slower response times and can exhibit dark-level smearing. See VA panel pros and cons.

Zone Count and Blooming: What to Expect

Zone count is the most important specification for local dimming quality. More zones mean smaller zones, which means less blooming. But zone count alone does not tell the whole story. The algorithm that controls the zones also matters. A monitor with 384 zones but a slow or poorly tuned algorithm can still show visible blooming and haloing.

Here is a rough guide to what you can expect:

No local dimming: Blacks appear grey. HDR is ineffective. Suitable only for SDR use.
8-16 edge-lit zones: Noticeable blooming. HDR 400 is the best you can achieve. Acceptable for casual use.
32-48 edge-lit zones: Moderate blooming. Some HDR 600 monitors use this configuration. Better than 8 zones but still imperfect.
384-576 FALD zones: Good HDR with minor blooming in high-contrast scenes. DisplayHDR 1000 possible.
1152+ FALD zones: Excellent HDR. Blooming is minimal. DisplayHDR 1400 possible.
OLED (per-pixel): Perfect blacks, no blooming. Peak brightness limited to about 600-800 nits for full-screen white.

If you plan to use HDR for gaming or watching movies, aim for at least 384 FALD zones. For professional HDR content creation, 576 zones or more is recommended. Edge-lit dimming is not suitable for critical HDR work.

It is also worth noting that local dimming can introduce haloing around small bright objects, such as a cursor on a black background. This is more noticeable with edge-lit dimming. Some users find it distracting, while others adjust quickly. If you work in a dark environment with a lot of text on black backgrounds, local dimming may actually reduce readability. In that case, you might prefer a monitor with no local dimming or an OLED.

Local Dimming and Response Time: A Hidden Trade-off

Local dimming can affect motion performance. When a bright object moves across a dark background, the zones must turn on and off rapidly. If the dimming algorithm is slow, you may see zone lag, a trailing brightness that lags behind the moving object. This is similar to motion blur but caused by the backlight rather than the liquid crystal response.

Some monitors allow you to adjust the local dimming aggressiveness. A faster setting reduces zone lag but may cause more blooming. A slower setting reduces blooming but can make motion look smeary. For gaming, a fast setting is usually preferred. For movies, a slower setting may look more natural.

Response time and overdrive also affect motion clarity. See what is response time and motion blur and overdrive for more detail.

OLED monitors avoid this trade-off entirely because each pixel switches instantly. However, OLEDs have their own motion issues, such as sample-and-hold blur, which can be reduced with black frame insertion (BFI).

How to Evaluate Local Dimming Before Buying

In Singapore, you can visit retail stores like Best Denki, Harvey Norman, or Gain City to see monitors in person. However, in-store lighting is usually bright, which masks blooming and poor black levels. To properly evaluate local dimming, you need a dark environment.

If you cannot test in person, look for reviews that include:

Zone count: Listed in the specifications or in professional reviews.
DisplayHDR certification: VESA DisplayHDR 600 or higher indicates the monitor has at least some local dimming capability.
Real-world HDR brightness: Measured in nits for a 10% window (small bright area). A good HDR monitor should reach at least 600 nits in a 10% window.
Blooming photos: Look for test images with white text on a black background. This reveals blooming clearly.

Also check the monitor warranty comparison and dead pixel policy in Singapore before purchasing. Some retailers, like Courts and Gain City, allow returns for dead pixels only if there are more than a certain number. Amazon.sg has a 30-day return policy for most monitors, but check the seller’s terms.

Local Dimming and Panel Type: Which Combination Works Best?

The panel type (IPS, VA, TN) interacts with local dimming in important ways.

IPS + FALD: IPS panels have wide viewing angles and good colour accuracy, but their native contrast is low (1000:1). FALD helps compensate, but you may still see some greyish blacks in dark corners where zones are large. This combination is common in professional monitors like the ASUS ProArt series. For colour-critical work, see design monitor buying guide.

VA + FALD: VA panels have high native contrast (3000:1), so even without local dimming, blacks are deeper. With FALD, the result can approach OLED-like black levels. However, VA panels suffer from gamma shift when viewed off-angle, and dark transitions can be slow. The Samsung Odyssey Neo G7 is a good example of VA + FALD done well.

TN + local dimming: TN panels are rare in modern monitors with local dimming. Their poor viewing angles and limited colour gamut make them unsuitable for HDR. TN is mostly found in high-refresh-rate gaming monitors; see TN panel pros and cons.

OLED (no backlight): OLED does not use local dimming because each pixel is self-emissive. This gives perfect blacks and infinite contrast. However, OLED monitors are more expensive and have a risk of permanent burn-in from static elements like taskbars. For many users, the trade-off is worth it. If you are considering OLED, read IPS vs VA vs TN vs OLED.

Practical Recommendations for Singapore Buyers

Your choice of local dimming depends on your use case and budget.

Office and web browsing (S$300, S$600): No local dimming needed. Focus on resolution, ergonomics, and connectivity. See office monitor buying guide.
Casual gaming and movies (S$600, S$1,200): Edge-lit dimming with 8-16 zones is acceptable. Look for DisplayHDR 400 or 600. The Dell S2722QC or LG 27UK850-W are options.
Serious HDR gaming (S$1,200, S$3,000): FALD with at least 384 zones. The Samsung Odyssey Neo G7 (S$1,499) is a strong choice. Alternatively, the ASUS ROG Swift PG32UQX (S$3,499) for top-tier performance.
Professional HDR content creation (S$2,000, S$5,000): FALD with 576+ zones and wide colour gamut. The ASUS ProArt PA32UCX-K (S$3,999) is a reference monitor used by video editors.
Enthusiast with no compromises (S$3,000+): OLED. The LG 27EP950 (S$3,299) or Dell U3224KB (S$4,599) offer perfect blacks and excellent colour.

Remember that local dimming is not the only factor. Resolution, refresh rate, colour accuracy, and connectivity all matter. For a complete overview, see the complete guide to choosing a monitor in Singapore.

The Future of Local Dimming

Local dimming technology continues to evolve. Mini-LED backlights, which use thousands of tiny LEDs, allow for many more zones than traditional FALD. Mini-LED monitors can have over 2000 zones, reducing blooming to near-invisible levels. Examples include the Apple Pro Display XDR (576 zones) and the Samsung Odyssey Neo G9 (2048 zones).

Micro-LED, which uses individual microscopic LEDs as pixels, promises the best of both worlds: self-emissive like OLED but with higher brightness and no burn-in. However, Micro-LED monitors are still extremely expensive and not yet available for consumers.

For now, local dimming remains the primary way to achieve good HDR on LCD monitors. Understanding its strengths and limitations will help you make an informed purchase.

The Complete Guide to Choosing a Monitor in Singapore
IPS vs VA vs TN vs OLED: Which Panel Type Is Best?
HDR Claims: What They Mean and What to Ignore
Colour Gamut: sRGB, DCI-P3, Adobe RGB Explained
VA Panel Pros and Cons
Motion Blur and Overdrive: What You Need to Know