CNET también está disponible en español.

Ir a español

Don't show this again

TVs

How QLED TV could help Samsung finally beat LG's OLEDs

Samsung is developing TVs based on quantum dot LEDs, pinpricks of light that promise even better picture quality than OLED TVs.

Most TVs today -- including all of those made by Samsung, Sony, Vizio and just about every other TV brand -- are based on decades-old LCD, or liquid crystal display, technology. In the last few years something better has come along, called OLED, or organic light-emitting diode. OLED TVs have the best picture quality we've ever tested, keeping LCD-only companies from achieving the coveted top positions on certain lists.

Now there's a new TV display technology on the horizon called QLED, and it might be even better than OLED. Short for "quantum dot light emitting devices," QLED has the potential to match the "infinite" contrast ratio of OLED, with better power efficiency, better color and more.

QLED could be the next big thing in TV tech. Samsung, the world's number one TV maker, has confirmed that it's working on developing QLED TVs for the commercial market, while continuing to deny it has plans to mass-produce OLED. That leaves Samsung's arch-rival LG as the sole manufacturer of OLED, and Samsung itself with plenty of motivation to work on an alternative like QLED.

Even for a company with the manufacturing clout of Samsung, QLED TVs are likely still a few years off, but you'll probably be hearing more about them soon. Here's what we know so far.

Quantum dots

For several years, many high-end TVs, in particular Samsung's SUHD models, have used what are called quantum dots. They're a way for LCD manufacturers to improve color reproduction and energy efficiency, and in our tests they do. The quantum dot-powered Samsung KS8000, for example, achieved higher peak brightness, and wider color, than any TV we've reviewed.

At this point you're probably asking...what the frak is a quantum dot?

Quantum dots are fascinating. They're microscopic molecules that, when hit by light, emit their own, differently colored light. Imagine shining a flashlight on a baseball and it glowing bright red. That's the general idea of a quantum dot, except way smaller. It's pretty mind-boggling.

The specific wavelength -- and therefore color -- of the created light depends on the size of the quantum dot. Larger quantum dots emit light in the red end of the spectrum, the smaller ones towards the blue end. So in the oversized example from before, imagine a marble next to the baseball. Your flashlight makes the baseball glow red and at the same time the marble glows blue. A golf ball in between might glow green.

What's the real size of these dots? Around 4 nanometers. As in, really, really small. Just a fraction of the width of a human hair.

QD now, QLED later

All TVs with quantum dots so far have used photoluminescent quantum dots. When a photoluminecent QD is hit by light, they emit their own color of light. In current generation TVs, these QDs work in concert with the blue LEDs that power the TVs' backlight.

The blue LEDs create blue light, and supply the photonic energy for two different sizes of quantum dots to create red and green and light. One method is to use a tube along the edge of the TV with blue LEDs wrapped with red and green quantum dots. Another, used by Samsung with its SUHD TVs, is to add an entire QD layer in the "sandwich" that makes up the LED LCD TV.

Quantum dots let LCD TVs offer wide color gamut (WCG) without losing a significant amount of light output. There's a problem, however: they're still LCDs.

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

Nanosys/Amanda Carpenter and Oleg Grachev

Contrast is extremely important for a good picture, and LCDs can't match the contrast ratio of other display types, like OLED or plasma. Local dimming backlights get them close, but not all the way. To get to that next level of picture quality, with lifelike contrast ratios, you need per-pixel control.

Enter electroluminescent quantum dots. Instead of an LED supplying light and that light causing the quantum dots to glow, electroluminescent QDs glow from directly supplied electrons. To use our oversized example from before, it'd be like hooking a car battery up to a baseball and having it glow bright red. Though I guess if you put enough current through a baseball it probably would glow red.

Shocking realizations about baseballs aside, electroluminescent QDs are more like every other light source you're familiar with, as in, an electric charge makes something glow. Like turning on a light switch, basically. This is a bit of an oversimplification, but it's the general idea.

The benefits of this are many, but the biggest is that per-pixel control I mentioned above. If you want a dark pixel, you can turn it off. No light emitted. You can't do that with LCDs, even with local dimming ("local" being a relative term). This is the key to better picture quality, and the main reason why OLED TVs usually look so much better than LCDs. QLEDs will have the same potential "infinite" contrast ratio as OLEDs, plus some additional benefits we'll talk about below.

And, like all quantum dots, it's relatively easy to fine tune the colors to whatever's needed. This could mean TVs could use formats like P3 for now, and Rec.2020 later, without needing to find all new materials or lose light with color filters.

qled-by-qdvision.jpg

Three electroluminescent prototypes.

QDVision

There's also multiple ways to do it, each with potential pros and cons. A manufacturer could choose to have each sub-pixel (red, green and blue) be electroluminescent quantum dots. Another manufacturer could choose to have electro blue, but photo red and green (sort of a hybrid). Another manufacturer could even have red and green photo QD, with an OLED blue.

Ah yes, OLED...

QLED vs OLED

The current generation of LG's OLED TVs use yellow and blue OLED materials to create "white" light. This is then filtered using red, green, blue and clear color filters. This is similar to how LCDs create color. There are many benefits to this, but they're pretty much all on the manufacturing side. As in, it makes OLEDs easier (read: cheaper) to manufacture.

There's a loss in efficiency which isn't too big a deal, but it makes getting a really wide color gamut difficult. A wide color gamut means less light with this method, so the OLEDs must be driven harder, or be more efficient. This doesn't mean it's impossible, it's just an additional challenge for a technology that has been struggling with challenges for over a decade.

RGB OLED would be the logical evolution, but these are even more difficult to manufacture in large sizes. Samsung actually made one itself a couple of years ago, but never followed up with additional OLED models.

The future

Two of the big players in quantum dots are Nanosys (used in Samsung TVs) and QDVision (used in TCL and others). Both are working on QLED, though of course are reluctant to share how far they or their manufacturing partners have gotten. Both companies speak of a glorious quantum future of bright, colorful, cheap displays, so easy to manufacture you could put them on a cereal box or make huge 4K displays with the best picture quality you've ever seen. We were promised this with OLED too, though.

I'm optimistic, however, for two reasons. First, we're already seeing photoluminescent quantum dots used in many TVs. They're becoming the go-to method for getting LCDs to produce wide color gamuts. Second, the architecture to get big flat panel OLED TVs working (which require more current sent to their pixels than LCDs), is in many ways the same architecture electroluminescent QDs need to work as well. Which is to say, OLED research has done a lot of the heavy lifting to get QLED working, without even meaning to.

And of course, keep in mind, we'll almost certainly see see non-direct view quantum dot TVs, i.e. LCD TVs with quantum dots, branded as "QLED." Just something to keep in mind.

The bottom line

I've been one of the most vocal proponents of OLED since long before there were any TVs we could buy. While currently there's a fairly wide range of models available, they're not as cheap as most of us would like, and they're only from one company, which is never good for a technology.

So I'm hopeful, but realistic. Quantum dots have lots of potential. Potential to match or succeed the best parts of the performance of OLED, plus a wide color gamut, lower power consumption and other benefits.

We'll certainly see more photoluminescent quantum dot LCDs, but direct-view electroluminescent "QLEDs" are still three to five years away. With any luck this won't be the "three to five years" we heard for over a decade about OLED. Most of the bugs that delayed OLED will help QLED work, so in theory they're fairly close.

We shall see.


Got a question for Geoff? First, check out all the other articles he's written on topics such as why all HDMI cables are the same, LED LCD vs. OLED, why 4K TVs aren't worth it 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 sci-fi novel and its sequel.