What is a Quantum Dot dispay? Is it better than OLED?

Most displays today — including all of those made by Samsung, Sony, Vizio and just about every other brand — are based on decades-old LCD, or liquid crystal display, technology. In the last few years something better has come along, called OLED, or organic light-emitting diode. OLEDs are genrally considered superior to LCD but as of now mostly it is a matter of preference to be honest.

The reason OLED displays are considered superior is because its a new technology, and it is already ahead of LCD, a much more mature technology, in various areas. Going forward as the OLED technology matures, it is sure to surpass LCDs. OLED displays may well replace the traditional LCD as the go to panel in the future, but it is facing competition from new display technologies too. 

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Quantum Dot technology is shaping up to be the next big step forward in LCD display technology, although we are yet to see our first smartphone implementation yet. The technology will likely be appearing in more devices over the coming years, but the science behind these new displays also boasts promising properties for other applications. Quantum Dot panels are seen as particularly promising, so let’s take a look at the differences with OLED and if it has what it takes to produce superior quality displays.

What is a Quantum Dot?

Before we begin, a quantum dot is a small nanocrystal made from various conducting materials, typically in the range of between 2 to 10 nanometers in diameter. Properties, such as light emission, are directly linked to the size of the nanocrystal.

Fixing the LED problem

In a very simplified nutshell, conventional LCD televisions pass light from an LED backlight through a series of color filters to create the images you see. To get the most accurate color, these color filters need to start with perfect white light, and herein lies the problem: LEDs can’t produce pure white light. The closest they can get is yellow. This is made from blue LEDs with a yellow phosphor coating.

As a result, the color filters have to work extra hard to block out everything but the red, green, and blue wavelengths needed to mix all the different colors in the visible spectrum. In the process, a lot of light energy is lost, and the resulting colors still aren’t very accurate — you get dim versions of imperfect red, green, and blue, and, therefore, relatively inaccurate color. That’s where the dots come in.

The Quantum Dot design replaces red, green and blue color filters with segregated stacks of quantum dots, which shine pure red, green and blue when exposed to a blue LED backlight. The colors you see are no longer filtered, they’re directly emitted, similar to an OLED or plasma display. A conventional LCD panel must still act as a grid of shutters behind these quantum dots to selectively block light from reaching them — that’s how we get blacks.

In traditional LCD displays, the display panels can’t completely prevent all of that white light coming from behind it from escaping; it’s especially apparent when the screen is supposed to be dark, or worse, totally black. That’s where the light bleed and halo issues reviewers are always complaining about come from.

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Although Quantum dots can emit light, current implementations use them as a filter on blue light.

Pixels can’t individually be switched off on Quantum Dot displays either, a property of OLED that allows for deeper blacks. But quantum dots are activated to glow by blue LED lights instead of yellowish-white ones, any “leaking” light will be toward the outer edge of the visible spectrum, which humans are less perceptive to.That should cut down on the nasty “halo” and “light blooming” effect that reviewers love to hate.

The end result should be a display with an exceptionally bright, vibrant picture, excellent color accuracy, much improved black levels, and superior shadow detail than a traditional LCD panel. The black levels are still not as deep as OLEDs but it’s extremely close. Therefore, OLED should still win out when it comes to contrast and high dynamic range imagery.

Some problems still persist

This leads us onto viewing angles, an area that OLED again boasts superiority over LCD displays and this is unlikely to change much with the introduction of Quantum Dot displays. Because backlight based displays require a filter layer rather than producing light directly on the surface, some light is blocked when you don’t look at the display from head on. While perhaps not likely to be a major problem on your small mobile phone, Quantum Dot displays won’t match OLED’s viewing angles until designs come along that eliminate the need for a backlight. When that happens, it will be called a QLED (Quantum Dot Light emitting diode) display.

Pricing

Perhaps the biggest factor in any technology’s success is its cost, which is one of the reasons why LCD is still so popular in mobile devices.

Although costs are falling, high quality OLED displays typically cost around 20 percent more to produce than the same size LCD panels. This is mostly due to the rather tricky production techniques required and lower yields. Fortunately, new manufacturing processes,  could see prices halve and OLED panel production costs could fall to 20 to 30 percent less than those of LCD by 2017.

It’s also worth considering that OLED based products have a shorter lifespan, due to blue pixel materials, and can also suffer from the dreaded “burn in” issue after a while. Quantum Dot displays don’t have from the same problem, as they are very stable over long periods of time.

Quantum Dot LCD displays retain many of the benefits of LCD’s lower production costs. The QD filter layer does not add a huge cost or complexity to the production of a display, as it is simply a mixed assortment of red and green dots rather than an intricately laid out matrix. However, the falling OLED prices may make Quantum Dot technology a tough sell in lower cost products, where LCD is currently commonplace.

Which is better?

Quantum Dot is certainly a viable rival to OLED, but it is more of an evolution of LCD than a likely successor to OLED panels. Both have their pros and cons, much like display types found on the market today. Quantum dots have lots of potential. Potential to match or succeed the best parts of the performance of OLED, plus a wide color gamut, lower power consumption and other benefits over the current gen LCDs.

We’ll certainly see more photoluminescent Quantum dot LCDs, but direct-view electroluminescent “QLEDs” are still three to five years away. With any luck this won’t be the “three to five years” we heard for over a decade about OLED. Most of the bugs that delayed OLED will help QLED work, so in theory they’re fairly close.

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