Mini-LED LCD TV tech: Tiny lights could lead to better picture quality - CNET

The latest new TV tech is called mini-LED. It first launched last year with TCL's 8-Series and is now available on the more affordable 6-series, starting at just $650 for the 55-inch size. With the promise of better contrast, mini-LED has the potential to offer improved picture quality compared to "standard" LCD-based TVs, at a cheaper price than OLED TVs. That's pretty much what our own David Katzmaier found when he reviewed the the 8-Series, saying "The TCL 8-Series has the best picture quality of any non-OLED TV I've tested this year."

Read more: TCL launches 2020 6-Series Roku TVs with mini-LED, QLED, local dimming

While TCL is first TV maker out of the gate with a mini-LED TV, it probably won't be the last. Mini-LED's advantage, aside from a snazzy new name, is that it's actually affordable. It's an evolutionary technology, not a revolutionary one, and draws on existing LCD TV technology.

Here's how it works, and why it's so cool.

Mini-LED is not MicroLED

Before we get started, know that mini-LED and MicroLED are not the same thing. MicroLED is a cool future tech that's reserved for rich people today, while mini-LED is currently available and in TVs as low as $650 for the 55-inch 6-Series. 

MicroLED displays, like Sony's Crystal LED and Samsung's The Wall, use millions of LEDs, one for each pixel. Essentially, you're looking directly at the LEDs which are creating the picture. And while each individual MicroLED is tiny, the modular nature of MicroLED means it can get truly gigantic.

Mini-LEDs are found inside normal-size TVs -- TCL is currently selling versions from 55- to 75-inches -- but the LEDs themselves are much larger than MicroLEDs. Just like the standard LEDs found in current TVs, they're used to power the backlight of the television. A liquid crystal layer, the LCD itself, modulates that light to create the image. MicroLED isn't LCD at all, it's a whole new TV technology that also happens to use LEDs.

Here's how the two stack up against one another as well as standard LED, QLED and OLED.

Bright lights, big TV, better local dimming

To understand mini-LED, you need to understand standard LED, at least as far as your TV is concerned. Inside all modern LCD TVs (i.e. every TV that's not an OLED), there anywhere between a few, to a few hundred light emitting diodes. These tiny devices emit light when you give them electricity and are being used everywhere in the modern world, from the flashlight on your phone to the taillights on your car. They range in size -- commonly they're around 1 millimeter, but can be smaller than 0.2 millimeter.

In some TVs the LEDs are on the edges, pointing inward. On others, the LEDs are behind the screen, pointing toward you. For improved image quality, particularly to appreciate high dynamic range (HDR), you need local dimming. This is where the TV dims the LEDs behind dark sections of the image to create a better contrast ratio between the bright parts of the image and the dark. For more on this, check out LED local dimming explained.

Ideally, you'd be able to dim each pixel enough to create a visually impressive contrast ratio. This is, for example, how OLED works. With LCD, though, it's much harder to do. The liquid crystal panel that creates the image only blocks the light created by the backlight. Not all the light can be blocked, so the image is grayer and has less "punch" than with OLED. 

Local dimming improves this issue, but it's not 1:1. There isn't one LED for each of the 8 million-plus pixels in a 4K TV. Instead there are thousands, if not hundreds of thousands of pixels for every LED (or more accurately, groups of LEDs called "zones"). There's a limit to how many LEDs you can squeeze onto the back panel of a TV before energy drain, heat production and cost become severely limiting factors. Enter the mini-LED.

Going big with little LEDs

Although there's no accepted threshold, LEDs smaller than 0.2-millimeter tend to be called mini-LEDs. They're often 0.1-millimeter or less. Not too small though: At around 0.01-millimeter, they're called MicroLEDs.

Generally speaking, when you make an LED smaller, it becomes dimmer. There's less material to create the light. You can offset this a bit by giving them more electricity ("driving" them harder), but there's a limit here, too, constrained by energy consumption, heat, longevity and practicality. No one is going to hook their TV up to a high-amp, home appliance-style outlet. 

As LED technology improves, they get more efficient. New tech, new manufacturing methods and other factors mean that the same amount of light is created using less energy, or more light using the same energy. New tech also allows for smaller LEDs.

TCL's 8-Series mini-LED has over 25,000 mini-LEDs arrayed across the back of the TV. These are grouped into around 1,000 zones. Both of these numbers are significantly higher than what you'd find in a traditional LED TV. The 75-inch Vizio Quantum X for example, has 485 local dimming zones. No TV maker aside from TCL officially lists the number of LEDs in its TVs, but it's safe to assume none have as many as 25,000 (yet).

Meanwhile, the new 6-Series is much less impressive at 1,000 mini-LEDs and 240 zones -- more than many models at its price but clearly not at the same level as the 8-Series.

If you were to take the LCD layer of the TV off, the mini-LEDs would create an image that would look like a low-resolution black-and-white internet video version of the show you were watching (see the pairs of image comparisons above). By being able to dim parts of the screen far more precisely, the overall apparent contrast ratio goes up. It's still not quite as good as being able to dim each pixel individually (like OLED and MicroLED), but it's far closer to that ideal than even the most elaborate full-array LED LCDs now. Check out the video below for TCL's own demo of the 8-Series in action.

Now playing: Watch this: TCL 8 series, 6 series boost Roku TV's picture quality...

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Having more zones is a big factor here, as it means improving two other aspects of the image. The most obvious is reducing the "blooming" typical of many local-dimming LCDs. Blooming is created because the local-dimming backlight is too coarse, creating light behind a part of the image that should be dark. 

Imagine a streetlight on an otherwise dark road. A local-dimming TV doesn't have the resolution in its backlight to only light up the pixels behind the street light, so it has to light up some of the surrounding night as well. Many LCDs TVs have gotten pretty good at this, but not as good as something that can dim each pixel. With mini-LED, you might not be able to light up individual stars in a night scene, but the moon probably won't have a halo.

Because there's less of a chance of blooming, the LEDs can be driven harder without fear of artifacts. So there can be a greater on-screen contrast ratio in a wider variety of scenes. The bright parts of the image can be truly bright, the dark parts of the image can be at or near totally dark.

The dark night returns

Deep blacks and bright whites are the Holy Grail (Grails?) of TV image production. Add in the color possible with quantum dots and you've got a the makings of a fantastic-looking television. With LG still the only company able to make OLED work affordably in TV sizes, other manufacturers need ways to create competing technology. LCD is still the only cost-effective alternative, and while it has come a long way, it's an aging technology. Mini-LED is the latest band-aid keeping it in the game.

As far as band-aids go, however, this is a pretty good one. The 8-Series looked really good, and is probably still a good deal before they run out of stock. The new 6-Series will be even cheaper, and will likely look great too, though we'll know more once we test one. That should happen soon. Hopefully more companies will announce mini-LED models, perhaps in January at the now online-only CES 2021.

Got a question for Geoff? First, check out all the other articles he's written on topics like why you shouldn't buy expensive HDMI cables, TV resolutions explained, how HDR works and more.

Still have a question? Tweet at him @TechWriterGeoff, then check out his travel photography on Instagram. He also thinks you should check out his best-selling sci-fi novel about city-sized submarines and its sequel.