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What is Local Dimming?

Updated Sep 17, 2014 By Cedric Demers
Vizio M Series FALD Off
LED TV with local dimming turned off
Vizio M Series
Vizio M Series FALD On
LED TV with local dimming turned on
Vizio M Series

Local dimming refers to the technology that changes the uniformity of the backlight of an LED screen. The television changes the luminosity of some zones of the screen to better reflect the scene and to create deeper blacks. It improves the weak black level of an LCD/LED TV.

Unfortunately, local dimming on LED TVs is rarely effective. Most LED TVs are edge lit, so they cannot control precisely the backlight. It works better on a full array LED TV (like shown in the pictures above), but it creates a blooming effect.

Unlike local dimming, Samsung Micro Dimming does not even dim locally the LEDs of the backlight. Instead, it is a software only feature that processes the picture to accentuate the contrast in different zones of the picture. More info on this later in this article.

In the pictures, you can see that the blacks for an LED with local dimming are darker than a normal LED because the lights behind that section of the screen are dimmed. However, you can see a slight halo effect, because the television still needs to have some bright LEDs behind the center cross. A plasma TV has no problem displaying deep blacks directly next to the cross.

Is local dimming worth it?

In theory, local dimming is great. It increases the perceived contrast of the picture by illuminating more the correct part of the screen and by turning off completely a dark section. LCD screens leak a little bit of light through the pixels, even when displaying a black color. By reducing the lights behind a region of the screen where the picture is mostly black, it reduces the leakage and produces a darker picture. The following illustrations show a backlight for a normal LCD, an edge-lit LED and a full array LED.

LCD backlight
LCD backlight
LED full array with local dimming backlight
LED full array backlight with local dimming
LED edge-lit with local dimming backlight
LED edge-lit backlight with local dimming

You can see that the backlight tries to match the picture to display, but there is some diffusion caused by the dispersion of the lights of the LEDs.

In practice, very few TVs can control precisely the backlight, due to the lack of a really granular backlight. The precision is not perfect and the size of the controllable zones varies between models. The worst case would be if you are watching a scene in space with stars. Overall, the scene is dark but the small stars are bright. The LEDs behind the screen affect a rather large area so it cannot only light up the backlight for the pixels of the stars. Depending on the implementation, it could produce a worse picture than before and could create a halo effect around the stars.

A full array backlight is not a guarantee that it is good. Here are some videos that we shot when we reviewed the Vizio M Series and the P Series:

As you can see in the videos, the full array local dimming of the P Series is a lot better than the M Series. Not only the added zones make difference, but it is also faster to match the picture.

The backlight cannot catch up on the Vizio M552i-B2. At first, it fully illuminates the dot. Once it starts moving too fast though, the backlight doesn't have time to turn on completely, reducing the luminosity of the dot. This is not an issue on the P Series. The backlight is more responsive. However, the backlight takes some time to dim down, leaving a trail of blooming.

What is Micro Dimming and Micro Dimming Ultimate?

Micro Dimming is Samsung's marketing response to local dimming (which is why the name is similar). However, Samsung does not actually dim the LEDs of the backlight, so it is not really local dimming. Instead, it artificially tries to create a similar effect by changing the contrast of different zones of the picture. Micro Dimming Ultimate claims to have twice the number of zones (600) and changes the color and sharpness in addition to the contrast.

Of course, this is mainly just a marketing feature and is nowhere near real local dimming. Video purist especially do not like it, because it messes with the video settings of their televisions, changing the contrast from frame to frame.

Which is why in all our reviews of Samsung TVs, we always set the mode to Movie to disable this feature.

You will not really see a difference between the different versions of Micro Dimming. As usual in the television business, the difference between them are more in term of marketing rather than real technology improvements. Therefore, we do not recommend the Micro Dimming technology. However, Samsung do put better panels in their higher end models, so the picture could be better (but not due to this technology).

Samsung TVs equipped with Micro Dimming are also equipped with CE Dimming. CE Dimming does dim the LEDs of the panel, but not locally. It dims the whole panel on darker scene. Some people do not like it, because you can actually see the whole screen dims sometimes, like in the end credits of a movie. There is no option to turn CE Dimming off, even in the service menu.

You can turn CE Dimming off indirectly though, by using the Movie picture mode.

What is Smart Dimming?

Smart Dimming is Vizio's name for its local dimming technology. It is used on some of their edge-lit LED televisions to dim the darker portion of the picture (see above for more information on local dimming for edge-lit televisions). The number of controllable zones varies depending on the model, but because it is still an edge-lit LED TV, we do not recommend that feature.

What is Frame Dimming?

Frame Dimming is the equivalent of an edge-lit local dimming, but with even less zones. Instead of changing the light for a specific region of the screen, it is the whole frame of the screen that changes intensity. You can see it as a very basic version of local dimming. It is better than no dimming at all for dark scene, but it is nowhere near real local dimming.

Does local dimming also work for edge-lit LED?

The majority of televisions with local dimming are edge-lit LED TVs. The resolution of the backlight of an edge-lit is a lot worse than a full array (see pictures above). The lights are on the edge of the screen, making it harder to control exactly a section of the screen. Instead of dimming a specific part of the screen, it is roughly the whole screen that will dim. It cannot be precise and it does not want to dim the brighter part of the image, so it will only slightly dim the darker parts.

To learn about the different types of backlight in an LED TV including edge-lit, check out how they work.

Here is a real example on an edge lit TV:

Samsung H8000 Local Dimming Off
Edge lit LED TV with local dimming turned off
Samsung H8000
Samsung H8000 Local Dimming On
Edge lit LED TV with local dimming turned on
Samsung H8000

The difference is really subtile. Because it is edge lit, it cannot improve the blacks inside the actual picture. Instead, only the top and bottom black bars are dimmed. It does overlap on the picture though. The top and bottom edges of the picture are darken.

Therefore, local dimming on edge-lit LED TVs (the majority of them) is not worth it. Only full array LED TVs can be effective, and they are very rare.

Can you turn local dimming off?

Yes, the local dimming feature of most televisions can be turned off in the settings menu. It is sometimes hidden inside the service maintenance screen.

For Samsung TVs however, Micro Dimming cannot be turned off even in the service menu. If you want to watch television without it, you will need to set your TV in the Movie Mode, where this feature is disabled by default (among other features also).

Does a plasma TV also have local dimming?

Plasma TVs do not need local dimming, because they have no backlight. Each pixel emits their own light and are independent of each other, so it can produce a white color right next to a black color with no leakage. Therefore, plasma do not have the problem that the local dimming technology is trying to solve for LCD/LED displays.

Learn about how plasma works here.

Conclusion

Unless it is a full array LED TV with a good implementation of local dimming, skip that feature. It does help with the blacks, but it can create a blooming/halo effect. Local dimming is even less useful for edge-lit LED TVs (most of them), because it cannot dim only a specific part of the screen.

Questions

Apr 08 2013
Is there a difference between the Samsung F6300 and F6400? I think the 6400 has micro dimming (and 3d but thats another thread), will micro dimming make it noticeable on these 2013 models?
The two main differences are 3D and Micro Dimming. If you do not care about 3D, you are probably better buying the F6300. Unless the price difference is really small, micro dimming alone is not worth it.
21
Sep 11 2012
How do I turn off Micro Dimming on my Samsung UN55ES8000?
Sadly, you can't. Even in the service menu, there is no option to turn off Micro Dimming on the Samsung models for 2012. You can however set the TV in Movie mode, which has that feature turned off (but also with other settings).
16
Mar 04 2013
I recently picked up a Sony XBR8 55". It seems to have a problem with the local dimming and frame doubling board. It'll cost about $200 to replace it. How does that television compare to current model televisions with local dimming?
The Sony 55XBR8 is a really good TV, even for a 5 year old TV. Not only it is a real full array local dimming, but the LEDs behind it are not white; they are separate colors in packs (2 green, 1 red and 1 blue). It still has a slight halo effect like most full array though. While the top TVs of 2012 are better, the 55XBR8 is in the same ballpark. Therefore, it is worth repairing it for 200$ instead of buying a new TV.
6
May 09 2014
I am trying to decide on a Samsung LED TV, the HU8550 or the H8000 LED. Which one is the best all around 55"?
We haven't test the HU8550 yet but we did test the H8000. Besides the 4k resolution, we don't expect a difference in the picture quality. So if you sit at more than 7 feet, go for the H8000 because you won't notice the 4k resolution anyway at that distance.
Update: We tested the HU8550, and the picture quality is indeed almost identical (except for the resolution of course). Go for the one that cost less.
4
Dec 11 2012
Is it better to buy a Samsung plasma 42" or the Samsung LED EH5300 40", as you said that there is no models in Samsung coming with full array with local dimming?
A Plasma TV and an LED TV are two completely different beasts, check out our guide here. If you are worried about blacks (hence looking for a full array local dimming model), you better go with a Plasma then. They are not for everyone and they comes with their own set of drawbacks, so make sure to check out the guide.
3
Nov 04 2012
I am on the edge of buying a led/plasma tv (42") but can't decide on it. I am told that led only makes sense when it is full array local dimming. But again it is very expensive. I like plasma display, but am hesitating for its heating & power consumption. Advices for led(which technology) or plasma, with brand and model names is appreciated. Thanks. Vinod
Local dimming is only good for full arrays, but an LED backlight is still worth it for its thinnest and lower power consumption compared to a traditional LCD backlight. Plasma do offer better picture in dark rooms though. If you check out our LCD vs LED vs Plasma guide, you will see that it cost only about 20$ more per year for a 42" plasma for electricity. There are very few good plasma model at 42", the best one probably being the Panasonic 42UT50.
2
May 06 2013
My question is what are typical difference on US and Europe's TV's? Is it about Hz only?
It depends on the model and country. Generally, it is only law compliance differences but sometimes some software features are different. Some country also get more sizes than others, mostly to accommodate the supplies.
2
Jul 01 2013
What are the 32" full arrays local dimming led TV models for LG and Samsung?
They don't exist. Full arrays are only available on big size TVs. A lot of them are direct lit though.
1
Aug 04 2014
Any suggestions on whether to buy the new Vizio m492i-b2 in terms of picture quality with the implementation of the new full array local dimming? According to cnet, the new Vizio tv has amazing picture quality. I'm on the fence with the vizio or the sony KDL48W600b.
We will start testing Vizio TVs soon. We don't have high hopes for the full array local dimming on them. We expect our actual contrast ratio measurement to stay unchanged even with that option turned on because we use a checkboard pattern. Keep in mind that CNET uses a 95% black pattern for its black level test, which favors local dimming (even edge).
Update: The review of the M552i-b2 is up now.
1
Jul 13 2012
I hesitate between two HDTVs, one with local dimming, and the other not. Should I buy the more expensive one?
If all other things are equal, no, it is not worth it. Most likely, you will not see the difference especially if it is an edge-lit LED screen.
0
Jul 06 2013
Why don't manufacturers use full array local dimming in all their large flat panel LCD/LED sets?
It greatly increases the cost of the display as well as making the TV thicker. Also, it doesn't improve the quality of the picture by a huge amount.
0
Jun 12 2014
What is micro pixel control in LG TVs? Does it give significantly better picture?
It is LG's name for local dimming. Its effectiveness depends on the model, but most models aren't very precise.
0
Aug 25 2014
Lg 70lb7100: LED backlighting - says along with micro pixel control, tru black control, a resolution upscaler and triple XD engine delivers amazing brightness, clarity and color detail. What does all this mean and is this tv full array or edge lit?
This is all marketing talk. It just means it is an edge-lit TV with local dimming.
0
Sep 04 2014
Eco sensor on or off for the Sony kdl42w700b?
The ECO sensor is just an ambient light sensor that adjust the luminosity of the screen depending on your room. It doesn't affect the picture quality. Some people prefer turning it off to have full control over the backlight, others leave it on to prevent changing settings between daytime and nighttime viewing.
0
Nov 21 2014
How do I know which TVs are full array? Are there other terms the manufacturers use to identify full array?
Very few TVs are, so they when they do, they are explicit about it. They are using fancy terms (like Samsung's 'Precision Black Local Dimming') when it's not. In the low to mid end level, only the Vizio TVs are.
0
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