How Local Dimming Works on an LCD TV: A Clear Explanation
You would have seen TVs named like full-array, edge-lit or mini-LED and wondered what they actually mean.
Basically, all those buzzwords point to one main feature found in most modern LCD LED TVs—local dimming.
Each of those terms just refers to a different way of doing it.
What is Local Dimming?
Local dimming is a technique used in LCD TVs to boost contrast.
LCDs need a backlight to produce an image.
As the name says, local dimming means dimming the backlight in specific parts of the screen.
This feature helps make dark scenes look better and more realistic.
On the other hand, self-emissive displays like OLEDs don’t need this feature as their pixels light up on their own.
Why is Local Dimming Needed on an LCD TV?
Contrast plays a huge role in how good a TV picture looks.
Basically, the bigger the difference between the dark and bright parts of the screen, the more real and impressive the image feels.
That’s where OLED TVs really shine.
They’re are unarguably the best when it comes to contrast. Why?
Because each pixel on an OLED can turn itself off completely, meaning you get true, deep blacks.
No light at all where it’s not needed. This makes the image pop and feel very much lifelike.
But regular LCD TVs can’t quite pull this off, as they use a backlight (usually composed of LEDs) that’s always on, shining through the pixels to create the picture.
So even in scenes that are supposed to be totally dark, there’s still some light bleeding through, making the blacks look more like dark gray.
Because of that, picture on LCD TVs often doesn’t have that same level of realism that OLEDs do.
So does that mean OLEDs are the only good TVs out there?
Not really. OLEDs may win in contrast, but they’ve got their own set of problems—like burn-in, where parts of the screen can get permanently marked if the same image stays too long.
Plus, OLEDs usually don’t get as bright as LCDs, which can be an issue in super bright rooms.
On the flip side, LCD TVs don’t have to worry about burn-in, and they’re generally brighter because of their strong backlight.
If they could just improve their contrast, eventually the black levels, they would seriously rival OLEDs.
The way they try to do that is with a feature called local dimming.
I hope, by now you have understood it.
Wondering how local dimming works?
Let’s break it down in the next section.
How Does Local Dimming Work on an LCD TV?
The backlight in an LCD TV is generally made up of a large number of tiny little LEDs, how many depends on the model.
Now, if the TV lacks local dimming feature, all those LEDs pretty much work together.
They get bright, dim, or dark at the same time.
So, imagine you’re watching a scene with a bright sunrise.
The whole backlight lights up to show the bright sun clearly.
That part looks good.
But here’s the catch: when everything lights up like that, the small, subtle details, like faint stars in the sky or shadows under trees can get washed out or just don’t look as real.
That’s why the contrast isn’t that great on TVs without local dimming.
Now compare that to an OLED TV, where each pixel is its own light source.
Every single one can turn on or off completely, so you get perfect blacks with high contrast.
For an LCD TV to come close to the OLED-level contrast, it should be able to control its backlight in much smaller sections, or ideally down to individual pixels.
But here’s the thing—controlling each pixel like OLEDs do isn’t really possible for regular LCD TVs, because the backlight might have just a few dozen LEDs (in cheaper models) or up to a few thousands (in higher-end ones).
That said, if you can control the existing number of LEDs in the backlight, you can still boost the contrast.
Now, controlling every single LED separately is difficult and expensive, specifically when they are more in number.
So most TVs take a more efficient route, they divide the LEDs into several groups, or commonly known as zones.
Each zone lights up or dims depending on the brightness of the specific part of the screen.
So if a scene has a dark portion, only the LEDs in those particular zones dim down, helping create deeper blacks.
This feature is called local dimming, and it definitely helps improve black levels and contrast.
But how good its result is really depends on how well the TV does the local dimming—some do it better than others.
Types of Local Dimming
Local dimming can be implemented in several ways on an LCD TV.
You may have heard “this edge-lit IPS display comes with 100 dimming zones”.
That said, a TV with the same number of dimming zones implemented on a VA panel may yield a different level of improvement in contrast compared to an IPS panel.
So let’s first go through all the factors on which local dimming depends.
On Which Factors Does Local Dimming Depend?
How effective local dimming is, mainly depends upon these key factors:
- Placement of LEDs in the backlight
- Number/size of the LEDs/dimming zones
- Screen size/resolution
- Type of LCD panel used
- Local dimming algorithm
Let’s discuss them one by one.
1. Placement of LEDs in the Backlight
LEDs in a TV’s backlight can be arranged in a few different ways around the screen. Let’s quickly go over them.
A. Edge-Lit
Edge-lit TVs get their name because the LEDs are placed around the edges of the screen, pointing toward the center of the screen.
There are a few ways in which they can be set up.
LEDs might be all around the edges, or just on the top and bottom, or only on the sides.
Think of these LEDs like little flashlights on the edges pointing inward.
To spread the light evenly across the screen, there are light guides that help direct the light from each LED.
Since the lights are all around the edges, the picture tends to be brighter near the edges and dimmer toward the middle.
That means edge-lit TVs usually don’t have the best uniformity or contrast.
But with efficient light guides, they can still look pretty good overall.
The big plus?
Because the LEDs are only around the edges, these TVs can be really slim.
They also use less power since there aren’t as many LEDs inside.
That’s why a lot of LCD TVs you see are edge-lit — they look sleek, save energy, and still deliver decent picture quality.
Each of the LEDs present in the backlight of an edge-lit TV can be controlled either separately, or the LEDs can be grouped into zones that are individually controlled.
B. Full-Array
Full-array TVs have LEDs spread all across the backlight, pointing directly towards the screen.
The LEDs are not spread just around the edges like edge-lit TVs.
So, they usually have way more LEDs than the edge-lit ones.
These LEDs are split into zones that can be dimmed separately.
Because the LEDs are spread out evenly, full-array TVs usually deliver a very uniform picture quality with no bright edges or dimming at the centers like you sometimes see with edge-lit TVs.
Plus, having lots of dimming zones means they have much better contrast than edge-lit TVs, and way better than regular LED TVs that don’t have any local dimming at all.
The downside?
Full-array TVs aren’t as slim as edge-lit ones because the LEDs have to cover the whole backlight, making the TV a bit thicker.
But with the newer, tiny “mini-LEDs” (think sand-sized LEDs), many full-array TVs are getting slimmer while packing in thousands of dimming zones.
That means they can offer crazy good contrast and still look sleek.
C. Direct-Lit
So, this isn’t really a type of local dimming, but TVs usually have this type of arrangement with LEDs if they don’t have local dimming.
In this setup, the LEDs are spread throughout the backlight behind the screen and shine straight through.
Now, you might be wondering how direct-lit and full-array TVs are different as you may find some direct-lit TVs also marketed as “full-array” TVs.
The main difference is that direct-lit TVs can’t dim their LEDs separately.
That means all the LEDs turn on bright together in bright scenes and dim down together in dark scenes.
Because of that, some small dark details might get lost when it’s bright, and vice versa.
But, full-array TVs usually preserve all those little details in the scene.
2. Number/Size of the LEDs/Dimming Zones
Imagine there’s a tiny star in a dark sky on your screen.
If the star is smaller than a dimming zone on the TV, that whole zone has to light up to make the star bright, while the zones around it stay dark.
This can cause an extra glow or halo around the star, called blooming, where the light kind of spills out or appears more than it should.
So basically, the smaller the LEDs or dimming zones, the better the TV can control the picture and avoid that glow.
Also, having more dimming zones usually means local dimming works better, at least if you’re looking at TVs with the same screen size, resolution, and panel type.
But this perception can change if you’re comparing different kinds of TVs with different specs.
3. Screen Size/Resolution
Suppose you’ve got two TVs.
One is 43 inches and the other is 65 inches in size, and both have 100 dimming zones.
Since the smaller TV has the same number of zones packed into a smaller space, each zone is smaller, so it usually does local dimming better.
Moreover, a 4K TV has way more pixels than an HD one (four times), so it generally needs more dimming zones to keep good control over all those pixels.
But again, this assumption can also change once you factor in the type of LCD panel the TVs are using.
4. Type of LCD Panel Used
It’s not just about where the LEDs are placed or how many they are in number that affects how good local dimming is, the type of panel matters too.
Usually, VA panels have better native contrast than IPS ones.
So, local dimming works way better on VA panels than on IPS.
When you combine VA panels with mini-LED backlighting, you get way better contrast than regular LCD TVs, and the black levels can get pretty close to what you see on OLEDs.
5. Local Dimming Algorithm
And not to forget, one of the biggest things that really impacts how well local dimming works is the dimming algorithm itself.
These algorithms figure out how bright or dark different parts of the screen should be and adjust the zones to make the picture look sharp and clear.
Since these algorithms keep getting better over time, newer TVs are usually expected to have better dimming control than older models of the similar price range.
Role of Local Dimming in HDR To really get the most out of HDR content, a TV needs to show every detail with the right brightness and accurate colors.
Full-array TVs with solid local dimming can hit high contrast, keeping the bright parts bright and the dark parts really dark.
Plus, because these TVs try to control light as better as they can, they end up showing very accurate colors.
So basically, TVs with good local dimming deliver punchy contrast and spot-on colors, making HDR content look vibrant and awesome.
Which TVs use the Local Dimming Feature?
When it comes to picture quality, OLEDs are pretty much ruling the game right now.
But almost every brand is trying to keep up by adding local dimming to their LCD TVs.
The cool thing about LCDs is that they come in way more sizes and price points, so there’s something for everyone.
That’s why lots of brands make TVs with either edge-lit or full-array local dimming.
Most LCD TVs you see are edge-lit because they’re simple to make, sleek in design and range from budget-friendly to mid-priced TVs, probably depending on things like how many LEDs they have or how many edges they do cover.
Contrast can vary greatly on them.
The pricier edge-lit models usually have better contrast than the cheaper ones.
For the fancy, high-end TVs, brands usually go for full-array local dimming.
These top LCD models not only have better contrast but often pack some extra cool features like quantum dots and mini-LED backlighting.
Local Dimming vs OLED
OLEDs don’t need local dimming because their pixels light up on their own, so no backlight needed.
Since each pixel can turn off completely, local dimming just isn’t a thing for OLEDs.
That’s how they get those crazy deep blacks and almost infinite contrast.
Only the top-tier full-array LCD TVs can come close to OLEDs in contrast, however, can’t match them exactly.
Advantages of Local Dimming
Local dimming is a game-changer for LCD TVs, it seriously boosts picture quality and helps them go head-to-head with OLEDs, which are usually known as the kings when it comes to contrast and picture quality.
Using local dimming in LCDs is pretty much always a win.
It improves contrast, color accuracy, and overall HDR performance, making scenes look way more real than what could be found on a normal LCD TV.
Disadvantages of Local Dimming
We’ve talked about a lot of awesome stuff when it comes to local dimming, but it’s not perfect either.
Sometimes, if it’s not done right, the dimming algorithm can mess up and dim areas that should actually stay bright.
This can make the picture lose some contrast and dark details.
Another issue pops up when the dimming zones are too big to show tiny bright spots properly.
This can cause a blooming effect or light leaking into nearby areas.
Plus, as local dimming depends on a bunch of many small things too, therefore just looking at the number of zones or the panel type doesn’t really help you pick the better TV.
There are a few other minor downsides too, but honestly, the benefits way outweigh the drawbacks.
Conclusion
After diving into local dimming tech, it’s clear that it’s a solid way to boost picture quality on an LCD TV.
In a nutshell, if you want those OLED-like blacks with LED’s bright highlights, without dropping a ton of cash, a TV with full-array local dimming is usually your best bet.
That said, new edge-lit TVs deliver good contrast and have a sleek design, and are also easier on your wallet.
