Quantum dots

Quantum dots
Quantum dot TVs explained

19 Jan 2015 | Rasmus Larsen |

TVs with "quantum dots" were everywhere at CES 2015, but is it just more marketing or does the technology offer real improvement? In this article we will explore quantum dots and explain what it means for your TV.

So why now?

The quantum dot is not a new invention. It was discovered way back in the early eighties and as the name suggests the dots are tiny nano particles of less than 10 nanometers in diameter.

Since discovering the small dots, companies have tried to use them to improve - among other things - solar cells, but the idea of using quantum dots to improve TVs came later. The industry talked about using them for a few years before Sony eventually introduced the first Triluminos TV with quantum dots in January 2013 in the W90 model. The tiny dots have since been implemented in the Amazon Kindle Fire in a not-so-successful manner.

Samsung SUHD with quantum dots


Fast forward to CES 2015 where we saw an avalanche of quantum dot TVs from Samsung, LG, Sony, Panasonic, Sharp, TCL and others. Or to be precise; LCD TVs with quantum dots. The timing may seem odd, but it is not more surprising now than it was in January 2013. At that time, Samsung and LG exhibited incredible OLED displays. The future looked bright, so Sony’s launch of the W90 was obviously a defensive move.

Only one of the two South Korean manufacturers have been able to mass produce the stunning OLED TVs, so Samsung is rolling out plan b. Other TV manufacturers also announced quantum dot TVs, prompted by the threat from OLED.

How it is implemented in LCD TVs

So how do you implement quantum dots in a TV? First and foremost we have to emphasize that these TVs are still LCD TVs. Behind the LCD panel are LEDs (light emitting diodes); either directly behind the LCD panel or along the edges. In front of the LEDs - and behind the LCD panel - manufacturers can add the sheet of tiny nano particles. When exposing quantum dots to energy in the form of light the particles become "excited" and can convert light into primary colors. The color depends on the size of the nano particle.

The purpose is to convert blue light from conventional LEDs to saturated primary colors. The light from a quantum dot is "pure" (for TV use) and better suited for picture reproduction. Potentially, this could mean a slight improvement in contrast and color saturation. It can also improve power efficiency because less light is wasted, but this is more relevant for mobile screens than TV screens.

What the manufacturers forgot to tell us is that most power efficiency results in quantum dot research are based on tests with a variant that uses cadmium. However, cadmium will be banned in most markets in the near future and the alternatives - cadmium-free quantum dots - are not nearly as energy efficient, so the screen needs to output more light.

The layers in a quantum dot LCD panel


But the most important difference is that 2015 LCD TVs will be able to increase the color space because of the quantum dots.

Quantum dots can increase the color space of LCD panels from today’s Rec.709 standard, which is a relatively small color space, to 90-98% of the DCI color space, which is the color space used fir movie theatres. No manufacturer had actually reached 100% of DCI at the time of CES 2015, but they are quite close.

A larger color space is by definition good, but there is a catch. By implementing a larger color gamut - from Rec.709 to DCI - all content will be reproduced in the larger color gamut, skewing colors. A typical red tone will appear much more intense, which was not the intention of the movie producer. TV manufacturers say that their algorithms can accurately select which colors to intensify, but as we already know this is exactly what the movie crew is doing in the studio. How do we want the picture to look? How does this combination of shades affect the mood of the picture? Etc.

There are of course methods to reduce the color space of a screen, but because quantum dots are placed in front of the backlight all light goes through. During a tech demo, Samsung told us that the JS9500 (which by the way uses LED local dimming to improve contrast, but this has nothing to do with quantum dots) - that is part of the S’UHD line-up- will stretch all content to the wider color gamut, even your own camera recordings, and that there is no option to turn it off. Unless Samsung changes its mind we could be looking at oversaturated and artificial colors.

This is not how it needs to be, but to actually benefit from a wider color gamut you need content - movies, TV series and games - in the DCI color gamut. The studios already have those because that is how movies are released in theatres, but there is still a difference between a movie color graded for a dark theatre and a movie color graded for a bright living room, so they need to do some remastering work before you can get your hands on movies in DCI. Right now, there is nothing out there. Not on Blu-ray, not on streaming services, and certainly not on TV channels. Sony has tried to push its x.v.Color on a few of the "Mastered in 4K" Blu-ray discs, but no other players support the initiative.

Sharp TV with quantum dots


The DCI color space is not part of the Ultra HD standard either, but we hear that the new Blu-ray standard will support it. Still, if the industry chooses to make a pit stop at DCI in the goal to reproduce Rec.2020, some standardization work has to be done.

In other words; there is no other way. Only when movies are released in the DCI color space will you be able to benefit from most important improvement in quantum dot LCD TVs. The lower power consumption will help enable HDR (high dynamic range) on LCD displays, but you still need a full-array local dimming LCD TV - and those are expensive. Quantum dot can be considered yet another brick on an aging LCD technology. Besides the color gamut, it changes none of the fundamental weaknesses of LCD panels.

An alternative to OLED?

Manufacturers were quick to compare quantum dot LCD TVs to OLED TVs in terms of picture quality. Samsung’s words "Rich colors, better than OLED" are certainly bold.

Still, all this marketing and all the side-by-side demos ignores the fundamental elements of why OLED display technology is unique. Just because you add quantum dots to an LCD panel you do not get the perfect blacks of an OLED. The same is true for the extremely fast response time and the near-perfect viewing angles. OLED technology is also approaching full coverage of the DCI color gamut, but it remains unclear how LCD and OLED will reach Rec.2020 - at least in the short term.

LG 4K OLED-TV


Quantum dot LCD TVs are promoted as "OLED picture quality at lower cost." The TVs may very well turn out to be cheaper, but during CES we noticed how it was only available in the most expensive high-end TVs. As the earlier photo shows, one way of adding quantum dots is with a film, or sheet, in front of the LEDs. This film can cost as much as 100 dollars during the production stage for a large-size TV, according to estimates from IHS. As you probably know a cost in the production stage multiplies by a given factor before reaching the consumer product.

No prices were announced during CES 2015, so we cannot compare at this point. However, it is very unlikely that quantum dots will make LCD TVs truly competitive with OLED technology, which is still superior in every respect - except perhaps the price. And it does not change the fact that unless Hollywood starts releasing movies in the DCI color gamut you will not be able to benefit from one of the most important improvements of the quantum dots.



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