Following this week’s announcement of Samsung’s QLED range, you may be looking for a quick explainer of what the “Q” in QLED is all about.
Simply – the Q is for Quantam dot. Quantum dots are nano-scale crystals that absorb light, then re-emit it at a different, very specific, wavelength. They basically do what the hydrocarbon semiconductors in an OLED TV does minus the organic chemistry.
Quantum Dots enable plasma-quality colour saturation that never fades, brighter panels with increased contrast, and wider gamuts – all while being relatively inexpensive to make.
But to understand why Quantum Dots in Tv’s are a thing now, we have to go back to hoe LCD works.
LCD: The Basics
Normal LED-LCD TV’s are made of the white back light, the pixels (each of which is divided into three coloured subpixels: red, green, and blue), and the LCD shutter (which acts like a tiny set of Venetian blinds, opening and closing over the individual subpixels to create various hues).
The back light shines light through each pixel on the screen to create a coloured dot – all together, these coloured dots make up the image you see – and the colour of that dot depends on the position of the LCD shutter.
So if the LCD shutter closes over a pixel’s red and green subpixels, the light comes out blue. If the LCD shutter only closes over the green subpixel, the light comes out purple (a combination of blue and red light). If the shutter closes over all three, it produces black. If it remains fully open, there’s white light…you get it.
By mixing the amount of light and combination of exposed sub-pixels, TVs can create millions of different shades of colour.
But there are downsides to this particular method of getting nice pictures on your telly.
The back light never actually turns off, it’s just blocked out by the LCD shutter, so it uses a fair whack of energy. The back light also needs a way to be fixed to the back of the screen – adding weight, thickness, and cost to the TV.
OLEDs don’t need the back light or to be fixed to the back of the screen. That’s why they can be so thin – and curved, too.
But the main thing is, the white back light in LEDs isn’t really white – it’s blue. A blue diode, more accurately, coated with yellow phosphor. The colour temperature is always a little bit off. Sop you can never actually get a super accurate on-screen colour.
Just Tell Me What A Quantum Dot Is Already
Quantum Dots make better back light. Starting in the best era for music ever, the mid-90’s, it was mainly used in infrared imaging devices. Come the noughties and TV manufacturers started eying it off, too.
Made from cadmium selenide, each quantum dot is a semiconductor nanocrystal. The size of the crystal is what decides the colour it will create, on a precise wavelength. It’s not chemicals providing a shade for a white source light. And that means the colour will never change, or fade. It will stay the same for the entire life of the crystal.
To make a TV screen, quantum dots are placed between two layers of semiconducting material. When voltage is applied to one side, electrons move to fill the holes within the quantum dot layer. This creates photons.
Light in a Quantum Dot TV is made by an uncoated blue LED. This travels through a tube filled with red and green quantum dots. The light “activates” the dots, they fluoresce, and creating red and green light. Combined with the blue LED light, this makes pure white light. And that’s how back lighting is created in a Quantum Dot TV.
Because they work like OLEDs – without an always-on back light – individual Quantum Dot lit pixels only turn on when they are needed. That’s about half the energy of an LCD screen of the same size, while being 50 to 100 times brighter and expanding the available colour gamut (the total theoretical number of colours a screen can produce) by up to 30 per cent.
But Quantum Dots have the leg up on OLED, as well – in some areas. The crystals don’t degrade over time, unlike the organic hydrocarbon chains used in OLED. They’re also far less susceptible to humidity and oxidation than OLED components. And since it’s only a single component of an existing display system, not an entirely new way of producing pixels, Quantum Dot technology can be integrated into panels for far less than what OLED sheets cost to make.
It also reduced the risk of screen burn. Sure, you can “refresh” an OLED screen to get rid of that pesky Food Network logo burned into the bottom right hand corner – but it’ll fade every time you do. Quantum Dots don’t have that issue at all.
In New York today, Samsung said the company has been constantly improving on the existing Quantum Dot technology, creating even more crystals that can emit even more colours.
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