Local dimming on monitors is a feature designed to improve contrast by deepening blacks and brightening highlights. It does this by turning off backlighting zones so that there's no light coming through those areas of the screen. That said, not all local dimming features are created equal, and it needs to be properly implemented in order to improve the picture quality. Otherwise, there could be haloing around bright objects on dark backgrounds or a loss of details in dark scenes.
We test local dimming using a video pattern and subjectively compare it to other monitors. We check how quickly the local dimming feature can react to changes on-screen and how effectively it can dim around bright objects on an otherwise black screen. We also clarify what type of backlighting it has, whether it's edge-lit or full-array.
Test results
Test Methodology Coverage
The local dimming testing has remained the same since our initial Test Bench 1.0 in October 2017. That said, we don't suggest comparing scores between monitors on different test benches because of the way we subjectively evaluate this test. When we test a monitor, we compare it to other monitors on the same test bench. What was considered good local dimming in 2018 is different than in 2026. Learn more about how our test benches and scoring system work.
| Test | 1.0 and newer |
|---|---|
| Local Dimming Video | ✅ |
| Local Dimming | ✅ |
| Backlight | ✅ |
When It Matters
Local dimming is meant to increase contrast by dimming the backlight behind dim or dark areas of the screen. This is supposed to increase the difference between those dark areas and bright objects in an image or video. Having an effective local dimming feature can improve picture quality with these deeper blacks next to bright highlights. This is especially important for having the best HDR performance.
However, a poorly implemented local dimming feature can lead to blacks losing detail or haloing around bright objects against dark backgrounds. This is often the case with edge-lit local dimming, where an entire backlighting column lights up around a small, bright object. If the local dimming on a certain monitor is so bad, you may prefer not using it. That said, some monitors don't allow you to turn it off in HDR, which means you have to pay attention to these test results if you want to buy that monitor.
Our Tests
Our local dimming score is based on the subjective impression we get from enabling dimming on a monitor. We consider performance from the video test from above, but also how well local dimming performs even with regular content.
We check the following:
- Sizes of the zones: The smaller, the better, and we also include in the text how many zones it has.
- Contrast and black levels: We see how much the black levels and contrast improve by using local dimming. We also measure this as part of our Contrast Ratio test.
- Haloing: We note if there's noticeable haloing around bright objects against dark backgrounds. You can see this in the test video, but we also check for it in regular content. We even watch content with subtitles to see how they look.
- Black crush: Sometimes when there's no haloing, a trade-off is that the local dimming is so aggressive that there's black crush instead. This mutes highlights and causes a loss of fine details in dark scenes, like a starfield. An effective local dimming feature will have no black crush or haloing.
- Zone transitions and speed: Using the test video, we see how well it handles bright objects transitioning between zones. If it's slow at turning zones on and off, this could be very distracting in action movies or games. If it's too fast at transitions between zones, the object doesn't fully appear as it should.
- Zone flicker: We verify if there's any visible flicker with local dimming enabled.
- Known issues: We also check for any problems that may arise when using local dimming, like when browsing the web or watching content. We make note of this in the text.
We repeat this process with different local dimming settings that a monitor may have, and choose the one that performs the best for the result and scoring. As this is a subjective test, how good any individual local dimming feature comes down to personal preference. You shouldn't only look at our score to determine whether you will like its performance on a given monitor, as you should also watch the local dimming video.
A perfect score would go to a monitor that can display bright highlights next to deep blacks without any haloing or loss of fine details. Only OLED monitors get a perfect score. Even though they technically don't have local dimming because they don't have a backlight, it's the equivalent of a perfect local dimming feature. It's nearly impossible for an LCD-backlit LED monitor to receive a perfect score.
Local Dimming Video
We film the local dimming video that we use to evaluate the performance, with an example below. We shoot off-axis, because sometimes issues like haloing around more visible from the sides than from directly in front.
We film at with a brightness of 100 cd/m2, and even if the monitor doesn't have local dimming, we still include the video so you can compare it to other monitors.
Local Dimming
We have a local dimming test result that acts as a Yes/No whether it has this feature. OLEDs don't have a backlight, so they technically don't have local dimming.
Backlight
The type of backlight can have a huge impact on local dimming performance. Our backlight test verifies the configuration of the monitor's backlight. Most of the time, we can see this with the test video, but we may also use thermal imaging to see how the backlights are configured.
We include the type of backlighting regardless of whether the monitor has local dimming or not. These are the main types of backlighting:
- Edge: Edge-lit monitors use strips of LEDs to light up the screen. They can be either along the top and bottom or on the sides of the display. Layers of diffusers are used to spread the light across the entire screen. Cheaper monitors usually have this, especially on those without local dimming.
- Full-Array: If you're wondering what full-array local dimming, also known as FALD, is, it has backlights placed all over the screen. The backlight is divided into zones, and the local dimming feature can adjust the backlight behind each zone. There are often more LEDs than the number of zones; they're grouped and controlled in clusters. Mini LED monitors are considered full-array. We also used to label monitors as having direct backlighting if they used full-array backlighting without having a local dimming feature. We no longer label monitors as such, though.
- No Backlight: If we label a monitor as having no backlight, it's because it uses an OLED panel. These displays don't have LED backlights, and instead, each pixel is organically lit on its own.
Additional Information
Advantages Of Using Local Dimming
A properly implemented local dimming feature can improve picture quality to the point where the monitor properly displays deep blacks next to bright highlights. This is especially useful for gaming or watching content in HDR. Not only that, but local dimming features often help the monitor get bright, so if you want to use it in a well-lit room, you should enable the feature.
See our recommendations for the best HDR monitors.
Which Panel Type Has The Best Local Dimming?
The panel and backlighting type have an impact on the local dimming performance. As mentioned earlier, OLEDs have the equivalent of perfect local dimming as they can turn pixels on and off. This results in perfect blacks next to bright highlights, which is what LED monitors strive for. Mini LED monitors are the best at this, but they aren't perfect. Some are too aggressive, resulting in black crush, while others have haloing around bright objects. You may prefer not using local dimming at all if that's the case. Monitors without this feature don't have black crush or haloing, but instead blacks aren't deep, and highlights don't pop like on Mini LED displays. As for edge-lit local dimming features, these usually fail to improve the picture quality while causing distracting haloing around bright objects, so there's no real reason to use this feature on an edge-lit monitor, unless you can't disable it.
You can see these differences with the four example monitors below. The edge-lit monitor looks the worst, with the most haloing, while the Mini LED monitors look almost as good as an OLED. However, the downside of the Mini LED display in the example below is that it has black crush in dark scenes, causing a loss of fine details.
| No Local Dimming | Edge-Lit | Mini LED | OLED |
|---|---|---|---|
| Dell S2725DC | Dell Alienware AW3225DM | BenQ MOBIUZ EX321UX | Dell Alienware AW3225QF |
Learn more about different monitor panel types.
Impact on Black Uniformity
Another way to see how the local dimming impacts the image quality is by looking at the photos in our black uniformity test. As we test with local dimming on and off, you can see how using the feature impacts uniformity. On edge-lit monitors, this is where you can see the obvious top-to-bottom haloing around bright objects. Below are examples of these black uniformity photos with and without local dimming on an edge-lit and a Mini LED monitor. It's clear that the Mini LED backlighting greatly improves uniformity by displaying an even black level throughout.
| Backlighting | Edge-lit | Mini LED |
|---|---|---|
| Monitor | ASUS TUF Gaming VG27AQL1A | KOORUI S2741LM |
| Without Local Dimming |  |
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| With Local Dimming |  |
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That said, having a local dimming feature doesn't guarantee good black uniformity, as it still depends on its performance. Even some Mini LED monitors have haloing around bright objects, as is the case with the AOC Q2740XMN.
How To Get The Best Results
There's no real way to improve a monitor's local dimming performance, but you can adjust some settings, as monitors offer different local dimming options. Low settings usually dim the backlight less, but they tend not to have haloing or black crush. Higher, or more aggressive, settings aim to improve the black levels, but can have black crush or haloing. These preferences are subjective, though, so if you have multiple options, try out the different settings and choose whichever one you like best. You may even prefer disabling it altogether.
On some monitors, local dimming can only be enabled, and even locked on, in HDR. If that's the case, you don't have much choice but to use this feature. If it performs terribly and distracts you, it's better not to use HDR.
If you're looking for a specific monitor with good local dimming, check out our recommendations for the best Mini LED monitors.
Conclusion
Local dimming is a feature that dims the backlight of monitors to improve black levels while making highlights stand out. It’s useful for watching content or gaming with a lot of dark scenes, especially in HDR. Good local dimming features often provide the best picture quality you can get on an LED-backlit LCD monitor. However, many monitors have poor local dimming performance, resulting in haloing and/or black crush, and negatively impacting picture quality. To test local dimming performance, we play a pattern video on each monitor with the feature enabled to see how well it performs. We then subjectively score the monitor based on whether a positive difference is made to the black levels and the picture quality in general, or if any downsides are introduced.