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How LCD TVs use mini-LED, dual panels and quantum dots to take on OLED

Who says you can't teach a decades-old display technology some new tricks?

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Cutting-edge LCD TVs like the TCL 8 series use mini-LED and QLED to improve picture quality but they're still not as good as OLED.

Sarah Tew/CNET

Liquid crystal displays, aka LCDs, are old. Really old. It's been 20 years since the technology's arrival on the TV scene, a period long enough to see the demise of CRTplasma and rear projection. LCD is still dominating the TV market against the remaining large-screen display tech, OLED. Compared to those other technologies the main advantage for LCD is that it's been relatively inexpensive to manufacture. That means dozens of companies around the world can build and sell LCD TVs profitably, leading to rapid decreases in pricing. As a result you can get huge screen sizes for very little money.

Despite its popularity LCD has inherent disadvantages in picture quality. Sure the best LCD TVs can make some amazing images, but compared to the best OLED TVs available, they come up lacking. The best-performing LCD TV of 2019, TCL's 8-Series, is a technological tour-de-force with both QLED and mini-LED tech augmenting its basic LCD display. It still fell short of the best OLED TVs from LG in CNET's side-by-side comparison, however.

That doesn't mean LCD makers like Samsung and TCL won't stop trying, and in many ways it's working. From different ways to drive the liquid crystal itself to improved local dimming, LCD image quality is dramatically better than it once was. With OLED going strong and MicroLED on the horizon, companies are continuing to figure out ways to overcome the inherent shortcomings of LCD technology to create better and better images. Here's what the (near) future will hold.

Mini-LED

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On the left, the image as you'd see it on a mini-LED TV. On the right, an illustration of the mini-LED array on the back of the TV. The ideal would be per-pixel illumination, but mini-LED is a step closer to OLED and MicroLED without the cost. 

Geoffrey Morrison/CNET

Mini-LED is an evolution of the LED backlight technology in nearly every current LCD TV. Across the back of the TV, tiny LEDs create the light that the liquid crystal layer manipulates so you can see an image. With the best current TVs, there are somewhere between a few dozen and a few hundred LEDs. With mini-LED TVs there are tens of thousands. 

You can see the effects of mini-LED in the two pictures above. On the left is the image as you'd see it on a mini-LED TV. On the right, there's an illustration of the mini-LED array on the back of the TV. With far more LEDs than a traditional backlight, mini-LED allows for a greater "resolution," so there can be finer distinctions between light and dark.

The 75-inch TCL 8-Series has 25,000 mini-LEDs grouped into around 1,000 addressable zones. The only other device we've tested that uses mini-LED, the Apple Pro Display XDR, is a 32-inch monitor with 576 zones. More zones means a far greater ability to darken the parts of the image that need to be dark, while the bright parts remain bright.

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TCL

The ideal, of course, is the ability to turn off individual pixels so no light is emitted. This is what OLED and MicroLED can do, and what plasma did. It's also essentially what CRT could do, though it didn't have "pixels" per se. LCDs allow you to dim a pixel, but some light always gets through. The only way to make a pixel black is by turning off the light behind it. Mini-LED improves on the current local dimming TVs with a finer control over what parts of the screen are lit, and which are dark.

Expect to see more TVs with mini-LEDs going forward. For more on this tech, find out how smaller lights could lead to big TV improvements.

Dual-LCD

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A diagram of how Hisense's dual-LCD tech will work: local dimming backlight (right), luminance-controlling LCD layer (middle), color-controlling LCD layer (left).

Hisense

Two is better than one, right? Hisense and Panasonic are working on that assumption to create a dual-layer LCD TV, meaning one with two liquid crystal layers. As mentioned above, the liquid crystal in an LCD TV manipulates the light. But some light always "leaks" through, which is why there's no true "black" (as in the absence of light) on an LCD without local dimming.

The idea behind dual-LCD is pretty simple: Add another layer of liquid crystal to help block more light. Amazingly, production costs of LCD TVs have dropped to the point that this crucial component is so inexpensive that manufacturers are considering adding another and still have an affordable TV.

The second LC layer is essentially doing the work of an elaborate local dimming backlight. Original prototypes used a lower-resolution panel for this function, but the model Hisense plans to ship in 2020 will have a second 4K panel, for a 1:1 ratio between the main LC layer and the one largely controlling the brightness. The idea here, apparently, is that adding a second LC layer and some additional processing will be cheaper than adding many LEDs, or many, many LEDs in the case of mini-LED.

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Some of the layers of Panasonic's MegaCon dual-LCD prototype.

Panasonic

Hisense will release a 65-inch dual-layer LCD TV in the third quarter of 2020 to the US market and says the price will be lower than that of a comparable OLED TV -- for reference LG's 65-inch B9 hit a low point of $1,800 last year. Panasonic showed its dual-layer Megacon TV at IFA last year but didn't announce a shipping date. It also intimated that the 55-inch display would be aimed primarily at professional markets.

Read more: Are dual-LCDs double the fun? New TV tech aims to find out.

Quantum Dots  

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Two vials of photoluminescent quantum dots next to a prototype blue photoelectroliminescent QD.

Nanosys - Amanda Carpenter and Oleg Grachev

OK, in fairness this isn't "future" tech as much as "current" tech. Many TVs have quantum dots today, from Samsung and TCL's QLED models to basically every midrange and higher TV Vizio makes. But their impact on LCDs and the display world merits a mention here. The wider colors of wide color gamut, along with the higher brightness levels of HDR, are easier to achieve with quantum dots.

The earliest LCDs with quantum dots had them as part of the LED backlight, while later versions had a thin QD layer. The latest models replace the color filters that let LCDs create color with films of quantum dots. As QD tech advances, and TV manufacturers come up with better ways to implement them, we'll get brighter and more colorful LCDs.

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The next-gen QD method. A blue LED backlight still creates all the blue light and the light energy for the QDs to glow, but now the quantum dots replace the color filters. Better efficiency and viewing angles are among the claimed improvements.

Nanosys

The next step for quantum dots, though, is much like the next step for LEDs. They'll likely ditch the liquid crystal and go direct view. That's a few years away, though. In the meantime Samsung is looking to build quantum dots into, wait for it, OLED TVs.

Not dead yet

Picture quality aficionados long lamented LCD's dominance in the TV market. They were brighter than other technologies and are usually the first to go to higher resolutions such as 4K (and now 8K), but they were lacking compared to other display tech.

This fact has never been lost on LCD TV manufacturers, though of course they don't say so publicly. Competition among each other, and against newer tech like OLED, means the R&D never stops to improve this old, old technology.

The fruits of that labor are visible today. TVs now, even inexpensive ones, look dramatically better than TVs from 10 years ago. These new technologies, and ones we don't even know about yet, show that LCDs will likely continue to improve well into the next decade.


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 cablesTV resolutions explainedhow 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 and its sequel.