Tom describes how QD-OLED displays differ from previous technologies.
Featuring Tom Merritt.
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I saw there’s this new kind of TV called QD-OLED
And there’s just OLED and QLED and WE led and get the led out.
What is this alphabet soup and why should I care?
Confused? Don’t be. Let’s help you know a little more about QD-OLED Displays.
QD-OLED is a combination of Quantum Dot and OLED display tech.
I’m going to keep these explanations as accurate as possible while still easy to understand, so TV-philes, please forgive me for leaving out some things like polarizers and diffusers. They aren’t unimportant but they can cloud the issue and send us down rabbit holes, so we’re going to stick to a somewhat simpler explanation. Thanks for your understanding and withholding your taunting “well actuallys.”
Let’s start with OLED, which stands for organic light-emitting diode. We covered OLED a little in our episode about MiniLED, but here’s what you need to know to understand QD-OLED
The benefit of OLED is that each pixel is its own light source. Other systems like LCD, shine a backlight on the pixels, which causes the dark parts of the picture to not be as dark as you might like, since there’s inevitably some bleedthrough. making the black areas slightly gray.
In an OLED display, the pixel itself provides the light. No backlight needed. OLED uses a carbon-based film- hence the use of the word organic- that produces light when two conductors pass a current through it. The light can be many colors but OLED TVs use blue and yellow. Those are combined to create white light that then passes through a color filter of red, blue and green subpixels.
LCD TVs block the backlight when they want it to be dark. With OLED when the pixel is off it’s completely off. There’s no backlight to try to block out.
That OLED pixel that’s off is completely dark, even when it’s right next to a bright pixel. This makes for excellent contrast. But there’s a trade-off. The peak brightness of OLED pixels isn’t as high. With LCDs you can just crank up that back light for a nice bright picture. If you overdrive the carbon-based OLED pixels they won’t last as long. Like you can cut the life of the TV in half.
LG– which makes all the OLED panels– sometimes uses a white sub pixel to bring extra brightness in, but that can wash out the picture.
SIDE NOTE: You noticed OLEDs start with blue and yellow to make white light then use a color filter to break them back into red green and blue. You could technically start with red green and blue OLED material instead of starting with blue and yellow. That would mean you wouldn’t need the color filter. Sony makes just such a 55-inch 4K monitor. Last I checked the retail price was $28,000. It’s just cheaper to manufacture the blue and yellow panels than the combined RGB one. At least for OLED.
And a quick note about burn in. Because you’re using organic materials there is a legitimate risk that the picture might get fixed. This happens, but it’s rare these days and display makers take a lot of steps to prevent it.
Finally OLED displays also have a wider viewing angle than LCD.
So that’s OLED. Now let’s talk Quantum Dot. You may have heard about Quantum Dot technology in TVs.
A quantum dot is not a Schroedinger’s dot that is both there and not there. However it’s not just called Quantum for marketing benefits. it really does take advantage of quantum physics.
And Quantum Dots are small. A few nanometers across. When light or electricity hits them an electron gets excited. You chemistry and quantum physicists types might say it goes from the valence band to the conductance band but the rest of us can just stick with excited. When the electron calms down– fine- “drops back into the valence band” it emits light.
Depending on how big the quantum dot is, it emits a different light. Or as the super smart people in the audience might say, “depending on the energy difference between the conductance band and the valance band.” Although if we go there we have to start accounting for instances in which band structure is no longer a good definition and that means we have to explain discretized energy states when really all you need to know to understand your TV better is that the size of the dot makes it emit a different color. Larger ones, say 5-6 nanometers are on the orange and red end of the spectrum and smaller ones – 2-3 nanometers- on the blue green end.
The nice thing about quantum dots is they don’t lose energy when they create the colors. It just sort of happens.
Now you noticed I said they can be hit with light or electricity.
The quantum dots in the displays you can buy are photo-luminescent. That means they need the backlight shined upon them to emit their color. This is opposed to electro-luminescent quantum dots that can create their own light with just an electric current. Electro-luminescent quantum dots are still in the lab for now. But we’ll circle back on that at the end.
Photo-luminescent quantum dots are used in QLED displays, a version of LCD TVs. QLED stands for Quantum Light Emitting Diode. They usually use a blue LED backlight shining on a layer of red and green quantum dots to make a pure bright white light. An LCD matrix controls contrast and a color filter converts the white light into the appropriate red green or blue. Because quantum dots are almost 100% energy efficient you get better color than other LCD TVs without losing brightness.
But, because you have that backlight, you need the LCD matrix to control contrast and thus you don’t have the deep blacks you have with OLED. Some QLEDs use Mini LEDs which helps some. MiniLEDs are smaller so you have more dimming control. Samsung calls these Neo QLED. But even then OLED still wins at contrast and black levels. And because QLEDs use a backlight they’re still less energy efficient than OLED.
So to recap. OLED’s are great for contrast but a little dimmer because of color filters. QLEDs have great color and brightness but not as good contrast.
So why not bring them together?
Hence, QD-OLED – Quantum Dot, organic light emitting diodes. QD-OLED displays start with just the affordable blue OLED materials, then combine those with red and green quantum dots. Your RGB is quantum dot R and quantum dot G with an OLED B.
So each pixel has three sub pixels. One is the blue OLED, then there’s a red quantum dot and a green quantum dot. Combine all three and you get true white light.
No pricey RGB OLED starting points. Just the affordable Blue ones. No LCD filter to control contrast you can do it pixel by pixel, just like in an OLED. No color filter. You have the colors in the quantum dots, right on the subpixels. You get the pure pixel by pixel control of OLED. You get the energy efficiency of quantum dots. And because there is no color filter, you get a brighter picture without worrying about overdriving the OLED material.
Vivid colors AND great contrast and deep blacks.
Samsung says its 4K QD-OLED panels have a million to one contrast ratio and .0005 nits of darkness and 1000 nits peak brightness. That’s really dark and really bright with great contrast if you’re wondering.
Because there is no LCD layer, the QD-OLED response times and viewing angle are better than QLED too.
QD-OLED TVs using Samsung-made panels were all over CES 2022 Sony developed QD-OLED TVs with them and Alienware made display monitors.
QD-OLED has the features to take over the preferred spot from OLED.
And before we wrap up let’s take a quick peek down the road. Remember we said there were also electro-luminescent quantum dots in the lab? If those can be made practical and cost-effective, you could get rid of the blue OLED, and just apply the current right to quantum dots to make them shine. Those panels could be even thinner, more flexible, colorful, bright and energy efficient without worrying about overdriving.
Right now only blue quantum dots can act as decent electroluminescent pixels. But if folks can get red and green working you might want to remember the acronym QDEL for Quantum Dot Electroluminescent panels. That’s a ways down the road though.
For now, I hope you know a little more about QD-OLED.
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