Quantum Dot and How It Affects Ultra HD Viewing Experience


Since the arrival of the first-generation 4K Ultra HD TVs, I’ve been saying that the increased resolution, on its own, may not provide enough wow factor that manufacturers need to inspire consumers to upgrade their televisions. At the typical TV screen sizes and at the typical viewing distance (with the tendency of being sitting far too far from the screen), the typical consumer may not be able to see the extra detail. Other potential elements of UHD–namely, better colour and contrast–provide a more obvious improvement viewed from any distance.

At the #CES2015, TV manufacturers emphasized two emerging technologies: quantum dots and high dynamic range. Last year, I wrote two articles about Dolby Vision and Technicolor high dynamic range technologies.  So today I will be discussing about Quantum Dot technology. What are they, and what do they do in a TV?

Quantum Dot is a manufactured semiconductor nano-crystal that converts incoming light into colours. The size of the Quantum Dot precisely dictates the colour it will emit (see the graphic provided below by QD producer Nanosys). As they relate to TVs, Quantum Dots affect colour performance in an LED/LCD TV. 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.


In these new QD-constructed TVs, a Quantum Dot layer 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 more accurate white light that moves through the rest of the LED/LCD TV chain. Because the white light is so precise, the TV’s blue, red, and green color filters don’t have to be designed to filter out so many unwanted colours, which preserves brightnessThis does not mean calibration is no longer necessary.  However, this means a better end result after the display have been calibrated and will stay calibrated for longer period of time.

So, the benefits of using Quantum Dots include purer colour, increased colour saturation, better brightness, and reduced electrical consumption. 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. LG is currently the only gigantic company introducing new OLED TVs to the market alongside with Skyworth, Hisense and TCL for the China 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 colour 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 Dot; they went with NanoCrystals…just to be different) 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, partnering with QD Vision, with its Triluminos TVs.

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 the graph below.


The thing is, none of the TVs on display at CES were touted as being capable of Rec 2020 color. In fact, the TV manufacturers I spoke with at #CES2015 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 colour 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.  However, since the whole point of home theatre is to reproduce the colour gamut of a movie theatre, DCI-P3 is a perfect match.

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).  When I asked this question to the Blu-ray Disc Association’s 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 colour 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 colour 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 colour” aspect of UHD is coming this year. The wider colour gamut, combined with a higher 10-bit colour depth (more possible shades of each colour), will deliver a step up in colour performance that will help distinguish many of this year’s UHD TVs from everything that has come before.

Clear as mud?  Good!





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