Quantum Dot Displays: Next Hot HDTV Tech?

In many ways it’s a sad time to be a videophile.  Plasma, which has long been the choice for discerning videophiles, is dead.  OLED, a display technology touted as plasma’s successor, has been slow getting out of the gates.  Yields have been constrained, display sizes have been relatively small, and some initial proponents have dropped their commitment.

This technology vacuum has left LED as the de-facto short-term winner in the display technology wars.  As manufacturers ramp up production of ultra high definition (UHD) displays, LED promises to be the dominant player for the foreseeable future.  However, as any hard-core videophile will tell you, LED-based displays leave a lot to be desired. Nevertheless, a new technology called quantum dots promises to address some of those shortcomings.

At this year’s Consumer Electronics Show (CES) in Las Vegas, quantum dot technology was a­ll the craze.  Aside from a name that conjures up images of your favorite Star Trek episode, what exactly are quantum dots and what benefits does this technology promise to bring to future UHD displays?  Basically, the promise of quantum dots is the promise of better color on LED displays.

What are Quantum Dots?

First of all, it’s important to clarify that quantum dots are not a new display technology.  They work on top of existing LED technology and are thus part of an LED display.   Traditional LEDs are made up of three parts: the LED backlight, the red, green, and blue color filters, and the liquid crystal layer that’s made up of the pixels we see on the screen. Each pixel is then made up of red, green, and blue subpixels which open and close depending on which color should be displayed.  Opening all the subpixels produces white and closing them all produces black.  To get different colors, a display will just combine the appropriate amount of light from the three subpixels.

Quantum dots, on the other hand, are tiny phosphorescent crystals that glow when hit with light.  They can glow in any color—not just red, green, and blue.  And here’s what’s cool about quantum dots: changing the size of the quantum dot changes the color it will glow.   So why is that important and what does it have to do with display technology?  Let’s find out.

What Are the Color Limitations of LED-Based Displays?

Most people don’t know that LED HDTV displays can only display a fraction of the colors that the human eye can see.  Some of this limitation is due to the color spectrum of HDTV’s Rec709 color standard—it’s limited to about 1/3 of the visible colors the human eye can see.  But the color rendition is also an inherent problem with LED display technology. Let’s understand why.

An exaggerated example of the difference in color between an LED display without quantum dots (left) and with quantum dots (right). Image courtesy of www.qdvision.com

If you’ve looked carefully at LED displays you’ll notice that most lack color purity and dynamics—especially when compared with other display technologies like plasma and OLED.   In fact, color on LED displays can sometimes come across as muted and dull.  With the increasing availability of UHD displays and the forthcoming expanded color gamut expected to be part of the UHD standard, the need to address LED’s color limitation has become even more acute; and it all starts with the color white—and because of this you’ll soon see why quantum dot technology becomes important.

If you ever look at LED lights—especially earlier generations—you’ll immediately notice a distinct blue hue to the light.  That’s the problem.  Unlike a pure white light, which can be divided into pure colors (think about a prism here), using an LED light brings about a slight shift in the color purity of the red and green hues because of its impure white light output.  If you think about the analogy, separating a blue light through a prism or shining a slightly blue light through a colored filter won’t give you the same purity of red, green, and blue colors.  You may be wondering why display LEDs aren’t covered by a film like some LED lights to shift their color output.  Well, they can be, and many are; but that still doesn’t address the color problem. Colors still come out looking muted.  Quantum dots are a much better solution.  They fix that color problem by helping LED’s blue light become a purer white.

Diagram of an LED display panel with a quantum dot layer.  "QDEF Exploded Diagram" by Jyurek via Wikimedia Commons

LED displays that feature quantum dots have a special quantum dot layer that’s sandwiched like an Oreo cookie between the blue LED backlight (the bottom layer) and the liquid crystal module (the top layer with the pixels and sub-pixels).  It’s important to note that the quantum dot layer isn’t arranged in pixels.  Rather, it’s a single layer spread across the entire panel that corrects the LED’s blue color to glow a more pure white.  As a result, the pixel and subpixel layer can now render colors more accurately and with better brightness and purity.  So, no matter what you read in a manufacturer’s marketing literature, the bottom line is pretty simple.  Quantum dots are all about color and nothing more.

What Quantum Dots Won’t Do

While quantum dot technology promises to do wonders with color on an LED display, it still doesn’t fix other inherent problems with LED-based display technology.  For example, quantum dots don’t improve the dreaded motion blur that LCD/LED-based displays are notorious for.  You’ll still get the soap-opera effect if you try and compensate for it.  Quantum dots also won’t make LED displays suddenly produce the beautiful black levels plasmas were known for and the absolute black OLED can render.

 For the discerning videophile, OLED-based displays will still be viewed as the preferred technology for future UHD displays.  However, until OLED becomes an affordable alternative for the masses in large display sizes, at least quantum dot-based displays will give the average users a foretaste of what lies ahead and an improvement over today’s LED displays.

Why Are Manufacturers Adopting Quantum Dots Over OLED?

As home theater enthusiasts, Audioholics members may be wondering why companies aren’t pursuing superior display technologies. Why are manufacturers continuing to try to put band-aids on top of LED technology?  It comes down to simple economics.  Unlike OLED panels, display companies are able to produce LED panels with very high yields.  That means LED panels cost less for the consumer. 

They also have all the manufacturing in place to produce these panels.  Adding a relatively simple process like quantum dots over an existing process requires relatively little investment and risk on their part.  So, whether we like it or not, LED technology is here to stay for the foreseeable future and we should expect more band-aids, like quantum dots, that will try to address the limitations inherent with LED-based display technology.

Are Quantum Dot Displays Worth the Added Price?

As with any new technology, companies will try hype up a new technology and make it a premium cost to consumers.  We saw this during the transition from 720p to 1080p displays; displays featuring motion enhancement at 120Hz or 240Hz; 3D-capable displays; and even smart TVs.  We expect the same to happen with quantum dot displays.  Consumers who want to take advantage of quantum dot displays will be paying a premium for this technology.  Over the next year or two, we expect that more and more displays will come with quantum dots as simply another feature.  However, if you want to jump into the UHD market and want the best that LED technology can offer today, then you owe it to yourself to check out LED displays that feature quantum dots.