CNET también está disponible en español.

Ir a español

Don't show this again


How quantum dots could challenge OLED for best TV picture

It won't happen this year, but when Samsung figures out how to make quantum dot TVs without depending on decades-old LCD technology, watch out LG.

Geoffrey Morrison/CNET

We've said it before but it bears repeating: Samsung's QLED TV technology is not the same as LG's OLED TV technology.

Sure they have similar names, down to the little slash that makes an "O" into a "Q," but according to CNET's tests for picture quality, OLED is superior. It's also fundamentally different from the LCD-based TVs that comprise the vast majority of the market today. Samsung's latest QLED TVs are still based on LCD, and while they have their strengths, they can't compete with OLED.

The "Q" in QLED, however, could change the game a few years down the road. It stands for quantum dot, a microscopic particle that could have a big impact on TV image quality. Samsung and other TV makers are working on technologies beyond QLED that could finally ditch LCD, and potentially challenge the picture quality dominance of OLED. 

No, I'm not talking about MicroLED. I'm talking about better uses for quantum dots. QLED is just the beginning of the quantum dot revolution, and it's only going to get cooler. Here's how.

A what?

Things have changed a bit since I discussed quantum dots in-depth before

The short version is that a quantum dot is a ridiculously tiny molecule that has many special properties, but the one we're most interested in is its ability to glow when supplied with energy. Depending on the dot's size it glows at a specific wavelength of light. So one tiny dot might glow green, and a slightly larger dot might glow red.


This not-to-scale diagram shows the microscopic quantum dots on the left and the orders-of-magnitude larger strand of hair on the right. If this were to scale, the QDs would be smaller than a pixel, or the hair would have to be larger than your screen. The size of the QD determines its color. 


This is useful to us because all we need to create a color image on a TV is red, green, and blue.

Currently quantum dot displays, like Samsung's QLEDs, use a thin layer of quantum dots in front of blue LEDs. The LEDs create, you guessed it, blue light. That blue light is not only all the blue you see on screen, but also the energy required to make the green and red quantum dots glow their respective green and red. So now you have all three primary colors, and all you did was run power to a bunch of really efficient blue LEDs. 


The most common current way quantum dots are used in an LCD TV. A blue LED backlight creates all the blue you see, plus supplies the energy for red and green quantum dots, applied as a separate layer, to glow their respective colors. Note how despite creating red, green, and blue light, it still needs to pass through a color filter to create the final image.


You can see this in practice in the image at the top of this article. A blue LED backlight is causing two squares of red and green quantum dots to glow.  

Since the colors created by the quantum dots is easily tunable, TV manufacturers are able to create the ultra-deep colors required by wide color gamut and HDR. QDs are also extremely efficient, so the TV can be brighter while using less energy than what'd be required with separate RGB LEDs or blue LEDs with a yellow phosphor.


On the left is an illustration of how many current LED LCDs work: a blue LED with a yellow phosphor. LG's OLEDs would be similar, just with blue and yellow spikes.

On the right is what quantum dot TVs can do, creating specific and tunable red, green, and blue light. Want a deeper red, a QD of a slightly different size can do that, and so on. This means richer TV colors with less light "wasted" using of inefficient color filters.


But this is just the beginning.

The near future: Quantum dot color filters

While the current use of QD increases the color and efficiency of LCD TVs, there's still an issue: the color filter. Right now quantum dots are essentially part of the LCD's backlight. Which is to say, the QDs and the blue LEDs create "white" light, which is polarized, sent through the liquid crystal, and then through a color filter. All these steps, and several more I didn't include, are required for you to see an image.

Color filters technically block light. They let through one specific color, but all the other colors are blocked. So in a standard LED/QD LCD, the backlight is creating red, green, and blue, but for each pixel, two of those are blocked and essentially "thrown away" to create a pixel the color you see on screen. Significantly more energy is being used to create the light than necessary.

The next step in QD and LCD is to replace the color filter with quantum dots. This improves efficiency dramatically. Since the TV is no longer tossing a huge portion of the light it creates, you can get the same light output with less power, or even greater brightness with the same power as before. Nanosys, a quantum dot manufacturer, expects a 3x increase in efficiency or brightness with this layout. There are also potential improvements to viewing angle.


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.


Right now the expectation is to use the same or similar blue LED backlight, and red and green QDs. But it's possible to use OLED as the light source. Since LG's current implementation of OLED requires color filters, this isn't beyond the realm of possibility. If they're working on it though, they're not saying.

We might see this tech in LCDs within the next year or so.


A closeup, using a loupe, of quantum dots arranged in a sub-pixel grid. This is just an example. In your TV these would be red, green, and blue.

Geoffrey Morrison/CNET

Direct-view quantum dot: The potential OLED killer

As cool as that is, there's still an issue: The LCD. Massive amounts of engineering and hard work has been done over the last few decades to overcome the inherent limitations of liquid crystal displays. Sure they've gotten pretty good, but they still have significant issues compared to OLED.

The next step for quantum dots is to ditch the liquid crystal entirely: Direct-view quantum dot displays. Instead of photoluminescence, the next-next generation of QD displays will be electroluminescent. 

Instead of blue LEDs supplying light to excite the QDs into emitting their light, this next-gen display will use electricity directly. Though QD manufacturers probably wouldn't love the analogy, this would be similar to how OLED works. A material, either OLED or QD, would get tiny amounts of current to glow a certain brightness. Cut off that current, the pixel goes dark. Send a lot, and it's bright.


The ultimate quantum dot display. No more LCD at all, just direct view quantum dots. This is essentially how OLED works, but instead of organic light emitting materials, it's quantum dots.


As you can guess, this means insane contrast ratios. More than that, it potentially means better brightness as well. Quantum dots are exceptionally efficient, so a smaller amount of current can result in a lot of light. So potentially these direct-view quantum dot TVs could be brighter than OLED, with the same black level, and with better color and longer life. That's the theory anyway.

As I mentioned at the top, since Samsung has already started using "QLED" in their marketing for their current-gen LCD TVs with quantum dots, that perfect name for this new, direct-view QD tech is off the table. So what do we call them?

"QDED" sounds cool, but perhaps a bit too metal. Nanosys is calling the tech QDEL, opening up lots of marketing opportunities for "Dude, you're getting a QDEL." On second thought, maybe just QDTV is simple enough.

The future is dots

If I seem excited about quantum dots, it's because I am. This is a fascinating and cool technology that could radically improve the picture quality of TVs. Beyond Samsung, other TV manufacturers like TCL and Hisense sell quantum dot models now, and Sony, LG and others have sold them in the past. I expect the trend to continue in the future. The major quantum dot makers have moved to cadmium-free QDs, so that toxic material isn't in TVs going forward (and can't be, due to EU law).

It's possible that soon our current benchmark for the best display tech, OLED, becomes the baseline, with QDED/QLED/QDEL being the step up in performance. Think about that! OLED becoming the lesser option for picture quality.

But then, of course, there could be further advances in OLED, maybe even QDOLED (Q-DOH!-LED) or something. Regardless, the future is bright. Literally. These things are super bright. 

Got a question for Geoff? First, check out all the other articles he's written on topics like why all HDMI cables are the sameTV resolutions explainedLED LCD vs. OLED 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.