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What Quantum Dots Mean to Your Next UHD TV

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Quantum-Dots-thumb.jpgSince the arrival of the first-generation 4K Ultra HD TVs, you've heard us say that the increased resolution, on its own, may not provide the wow factor that manufacturers need to inspire consumers to upgrade their televisions. At the typical TV screen sizes and at the typical viewing distance, the typical consumer may not be able to see the extra detail. Other potential elements of UHD--namely, better color and contrast--can provide a more obvious improvement. Well, 2015 marks the year that those other potential elements will become a reality, in both UHD TVs and UHD content. At the 2015 International CES, TV manufacturers emphasized two emerging technologies: quantum dots and high dynamic range. Over the next few weeks, we're going to discuss these technologies, along with the current state of HDMI, to give you an idea of where Ultra HD is headed.

We begin today with quantum dots. What are they, and what do they do in a TV? A quantum dot is a manmade semiconductor nanocrystal that converts incoming light into color. The size of the quantum dot precisely dictates the color it will emit (see the graphic provided below by QD producer Nanosys). As they relate to TVs, quantum dots affect color performance in an LED/LCD TV. That's right, we're not talking about a new display technology here. We're talking about a new way of constructing an LED/LCD TV. To understand how quantum dots work, you might first want to watch this refresher on how an LCD TV works.

Nanosys-QD-color.jpgIn these new QD-constructed TVs, a quantum dot layer (either a film sheet or a tube) is placed in front of the light guide panel. Instead of white LEDs for the back/edge lighting (or, more specifically, blue LEDs with yellow phosphor applied to make them white), these TVs use pure blue LEDs, which serves two purposes. First, the blue LEDs provide the blue element of the light. Second, the blue light passes through the quantum dot layer to create red and green. This combination of pure blue, red, and green creates a "cleaner" white light that moves through the rest of the LED/LCD TV chain. Because the white light is so clean, the TV's blue, red, and green color filters don't have to be designed to filter out so many unwanted colors, which preserves brightness.

So, the benefits of using quantum dots include purer color, increased color saturation, better brightness, and improved efficiency. It allows LED/LCD color performance to be more competitive with OLED color performance, yet it's far less expensive for TV manufacturers to implement right now. As you know, LG is currently the only company introducing new OLED TVs to the market, but that technology is expensive to produce, thus the TVs are expensive to purchase. Compared with existing LED/LCD TVs, QD-based LED/LCDs can offer step up in color performance without demanding such a big step up in price.

At CES, a variety of manufacturers showed off QD LED/LCD TVs, including LG, TCL, Hisense, and Samsung. (Samsung didn't use the phrase quantum dots; they went with nanocrystals...just to be different, I guess.) Different display manufacturers have teamed up with different quantum dot producers, including Nanosys, QD Vision, and DOW Chemical. Sony was actually the first LCD maker to use quantum dots in 2013 with its Triluminos TVs, partnering with QD Vision. Although the Triluminos name remains in use in Sony TVs, the quantum dots currently do not.

Some manufacturers are quick to point out that quantum dots aren't the only way to create a wider color gamut in an LCD. Both Sony and Panasonic claimed at CES that their current color technologies can produce a comparably wide color gamut, and LG is actually using two different approaches to color reproduction in its 2015 ColorPrime UHD TVs: some models use quantum dots, and others use LG's proprietary Wide Color Gamut LED.

What will we do with all this great color, you ask? This is where we talk about standards. Right now, our whole HD system is based on the Rec 709 color standard--from the content's creation to its display on your TV. When we calibrate HDTVs, we try to dial in the color points to be as close as possible to Rec 709 for accurate performance. A wider color gamut equals a less accurate color gamut by the Rec 709 standard. However, the proposed UHD Rec 2020 standard calls for a lot more color. I mean, a lot more. Check out our article The Color's the Thing That Will Make 4K So Amazing for further explanation.

Chromaticity-diagram.jpgThe thing is, none of the TVs on display at CES were touted as being capable of Rec 2020 color. In fact, the TV manufacturers we spoke with asserted that the Rec 2020 standard simply isn't attainable yet on the display side. Instead, the manufacturers touted that the "wide color gamut" TVs could reproduce (or at least get very close to) the DCI-P3 color space that's currently used in theatrical film content. DCI-P3 is a wider color space than Rec 709 but it's not as wide as Rec 2020.

How will this difference play out with upcoming UHD content, including Ultra HD Blu-ray--which is expected to support Rec 2020 when the final standard is released (likely in late spring or early summer)? We posed this question to the Blu-ray Disc Association, and Ron Martin, the vice chairman of the U.S. Promotions Committee, answered: "We describe BT2020 [aka Rec 2020] as a 'container,' meaning it is a signal specification that can allow a progression of color standards. BT2020 is very wide and covers a great amount of the human visible colors as a transmission signal. In the initial stages, that will be BT709, which most HDTVs carry now with normal gamma referred to as BT1886. Next will come the PQ gamma and HDR signaling that allows for high dynamic range displays. Then, as technology moves forward, the expanded color range of BT2020 will mature and become available on future TVs." Another noteworthy announcement at CES was the formation of the UHD Alliance, a consortium of manufacturers, technology producers, and studios whose stated goal is to figure out exactly how the technology should move forward and develop a workable roadmap for all UHD content.

Even though the specifics have not all been hashed out, the overriding message is that the "better color" aspect of UHD is coming this year. The wider color gamut, combined with a higher 10-bit color depth (more possible shades of each color), will deliver a step up in color performance that will help distinguish many of this year's UHD TVs from everything that has come before.

Additional Resources
CES 2015: What the Heck Are Quantum Dots? at IEEE Spectrum.
• Visit the Nanosys website for more details on quantum dot technology.
What Are Quantum Dots and Why Do I Want Them in My TV? at Wired.com.

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