Everyone, now a days, know the OLED very well. But what is OLED technologies and OLDE TVs. We will tell you in-detail here.
What is an OLED?
First a refresher: An LED (Light Emitting Diode) is a component that works on the basis of electroluminescence. In a traditional LED, the electroluminescent material is inorganic. For those who didn’t pay attention during chemistry class, organic chemistry deals with the carbon compounds and inorganic chemistry the rest. OLED stands for Organic LED (Organic Light Emitting Diode in full). In other words, it is an LED whose electroluminescent material is organic in nature.
For a very simple demonstration of a rudimentary OLED, take a look at Youtube .
How do LED and OLED differ in use?
A striking difference between an OLED and an LED has to do with the manufacturing method. You can consider an LED as a small point light source. The component must be built up on a semiconductor crystal and must eventually be sawn and mounted. We use LEDs as background lighting in an LCD TV (see below). But a TV with individual LEDs per pixel was almost impossible. With MicroLED that will change, although an affordable TV will not be available for a number of years.
An OLED is more like a flat radiator. The electroluminescent material can be applied over larger surfaces and will glow when current passes through. Moreover, we can apply these organic substances with techniques that are not possible with traditional LEDs. For example, some types of OLEDs can even be printed, which is a much cheaper manufacturing process. Instead of a glass substrate, it is also possible to work on a plastic substrate. This way we get a flexible OLED.
Why do we want OLED TV?
Why do we want to put that OLED technology in our televisions? Because it has many advantages, of course. OLED TVs are particularly thin, they deliver near-perfect contrast, better colors, an excellent viewing angle, very fast response time and therefore razor-sharp moving images, and are possibly more economical than our current television.
OLED TV vs LCD TV: These are the differences
So many benefits, how do they do it? The main reason: an OLED screen is an ’emissive’ technology. Each pixel of the screen itself emits light. An LED LCD TV, on the other hand, uses ‘transmissive’ technology. The light passes through a layer that will determine whether a pixel is on or off. How important that difference is becomes immediately clear on the basis of a diagram.
On the left you see the structure of an LCD screen. A backlight (BLU or BackLight Unit or backlight) provides the actual light. Nowadays, the BLU always consists of LEDs. The light is first polarized by the polarizing filter. The TFT is the actual control of the screen and determines how the liquid crystal is oriented for each pixel. Depending on the orientation of the crystal, the polarization direction of the light changes as it passes through the liquid crystal layer. The light then passes through a color filter and finally reaches the final polarizing filter. If the light in the crystal layer has changed polarization direction, it will pass through the last filter and the pixel will be on.
On the right you see the structure of an OLED screen. To begin with, it does not contain BLU. A TFT layer is applied to a glass substrate that drives each OLED pixel. The OLED layer is applied to it. Each OLED pixel itself produces light. A final glass layer with polarization filter closes the structure. Pixels are now turned on or off directly via the TFT control.
Different OLED implementations
Initially, in 2012, both LG and Samsung jumped on the OLED train. They did choose a different approach. Samsung used RGB OLED, where each pixel consists of a red, green and blue OLED sub-pixel. LG opted for WOLED – white OLEDs – where each pixel is white and is divided into a red, green, blue and an extra white sub-pixel with a color filter.
Although Samsung’s solution seems simpler, it has a significant drawback. Applying the red, green and blue sub-pixels is a difficult process: the organic elements are evaporated through a mask with the correct pattern. This has to be repeated three times, once for each color. The process is particularly sensitive to alignment errors or mask problems leading to color overlap.
LG’s solution avoids this problem by utilizing a single white OLED layer. Since all subpixels are white, a mask is unnecessary during vapor deposition and problems with alignment and color overlap are excluded. The pixels get their color by means of an additional color filter, just like an LCD TV. Because the light has to pass through these color filters, this solution is less energy efficient. LG therefore opted for four sub-pixels: in addition to red, green and blue, there is also a white sub-pixel. It should optimize consumption.
Unfortunately, the problems turned out to be too great for Samsung’s RGB OLED. A single model appeared on the market, but Samsung discontinued production after that.
OLED and Contrast
Contrast is mainly determined by how dark your black display is. In the LCD screen, this depends on the effect of the liquid crystal layer, which is unfortunately not perfect. Even when the pixel is ‘off’, light may still be visible. After all, the backlight is always on. That explains why the black value of LCD screens is not perfect. In recent years, a lot of work has been done on this, but the result cannot match OLED. When an OLED pixel is ‘off’, it produces no light at all.
The fact that the backlight is always on is the main reason for reduced contrast in an LCD TV. We also worked on this by using ‘ global dimming and local dimming ‘. In dark scenes, the backlight is dimmed completely, so that the image appears darker. A further step is ‘local dimming’. By dividing the backlight into segments, each segment can be dimmed separately or even turned off if necessary. This of course leads to better contrast.
But OLED still has the advantage. After all, OLED switches it on or off at pixel level, the equivalent of 8 million dimming zones (for a 4K TV). Not only is the black value better, an OLED screen can also display a perfect white and a perfect black pixel at the same time. And that results in an excellent contrast.
OLED and Brightness
OLEDs are quite efficient, just like regular LEDs. In other words, electricity is converted into light without excessive loss. The difference is in how much power we can send through an OLED without harming the material. In that respect, the OLED has yet to give up the LED. This manifests itself in two different ways. The maximum brightness that an OLED screen can achieve (with a correct D65 white point) is currently approximately 800 nits. LCD TVs can go much higher, up to 1,500 nits. But that’s measured when white only takes up 10% of the total screen area. When we show a completely white screen, the ABL (Average Brightness Limiter) intervenes with an OLED screen and the maximum brightness is about 130 nits. This is not necessary for LCD TVs, and the maximum brightness can then remain the same. In practice it decreases because too high a brightness on a completely white screen would be unpleasant. But LCD TVs that reach a peak of 700 nits will often still have 600 nits on a completely white screen.
OLED and Colors
OLED is able to display a wider color range . This is of no importance for SDR playback (still the gross of our viewing food). But for HDR reproduction , a larger color range is essential. The lead that OLED originally had here has disappeared because LCD TVs that use quantum dots deliver a very similar color range.
OLED and Viewing angle
The liquid crystal layer in an LCD screen is also to blame when it comes to viewing angle problems. You can best compare that with blinds. If the slats of a sun protection are not completely closed, you can see through them at certain angles. An LCD screen also has that problem. Again, this has been a lot of work done by using other structures in that layer, but the problem remains visible. OLED screens do not have that problem. Their viewing angle is significantly better, but still not perfect.
OLED and Motion sharpness
Blurry or double edges in a fast-moving image are a classic problem with LCD screens. The reason lies (partly) in the relatively slow reaction time of the liquid crystals. When we want to switch a pixel on or off, this does not happen immediately, but it takes a short time. As a result, pixels that should have been off are still partially visible and a moving object gets blurred edges in the image. Developments in panel technology have significantly improved response time (the best panels have a response time of 2 ms). But OLED TVs go one step further. By LCD’s 2ms response time, OLED boasts a 0.02ms response time. That is 100x faster and would therefore produce razor-sharp images.
Still, the difference is less dramatic than you might think. The reason? Both OLED and LCD use a ‘sample and hold’ method to display the image. A 50fps frame rate shows 50 images (samples), but they are each static on the screen for 20ms (hold). Because our eyes try to follow a moving object, that static image creates blurred edges. That, meanwhile, has more influence on how we see the image than the response time of each pixel. Techniques such as Black Frame Insertion can provide a significant improvement for both OLED and LCD.
Compared to an average LCD TV, an OLED TV is considerably sharper, but in the top category the difference is often nonexistent, or an LCD TV can even have a very slight advantage.
OLED and Consumption
A comparison of the schematic representation of LCD and OLED already shows that the light from an OLED TV has to pass through far fewer layers (and therefore suffers less loss) than that of an LCD TV. So if the efficiency of both light sources is approximately equal, an OLED TV would be more economical. Moreover, OLED pixels can be switched on and off individually, while with an LCD TV the backlight is always on. That too should be an advantage.
Yet in practice it appears that an OLED TV is not systematically more energy-efficient than an LCD TV. Depending on which LCD TV you compare with an OLED TV, it is possible that the LCD TV is more economical. Although we do note that the image quality also differs. With high-end models, OLED is still systematically more efficient than LCD.
Are there no disadvantages to OLED TVs?
The main hurdle to OLED commercialization has been the lifespan of the blue sub-pixels. It was too limited for use in screens such as our televisions. That problem has now been solved, but further research into more efficient materials continues (see last section).
In addition, OLED has been relatively expensive for a long time and was only available on large screen sizes (55 -65 inch). LCD TV has a massive advantage here. The production scale of LCD panels is many times larger, and the technology is much more mature, which translates into a cheaper cost. LCD is also available in many more sizes. The price of an OLED TV has fallen sharply in the meantime, but OLED remains reserved for the premium TV segment. Since 2020, smaller 48 inch sizes are also available. Also large sizes (77 inch and 83 inch) are now on the market, but we remain very expensive.
OLED TVs and burn-in
A real concern for OLED TV is burn-in. The organic material appears to be subject to non-uniform aging. Static content that you leave on the screen for a long time can then cause a lasting change. Manufacturers have provided all kinds of techniques to prevent this. We have written a separate article about OLED TVs and burn- in. The conclusion is that OLED TVs can burn in, but the risk is very low with normal use. Still, it remains a concern.
Further development of WOLED
The schematic of a WOLED panel that we gave at the beginning of this article is useful to understand its operation, but it is of course a simplification of the reality. To begin with, the white OLED layer is actually a stack of layers of different colors that together create white (a yellow and a blue, for example).
But even that is a huge simplification. In reality, for example, several blue layers are used. The construction of such a ‘stack’ is therefore extremely important. In addition, a lot of research is being done into other organic materials that can be used in the stack. For example with a longer lifespan, higher energy efficiency or even purer basic colors. It is therefore certainly possible that WOLED can evolve even further. A first step is, for example, the LG EVO panels that were used for the first time in the 2021 models. The real structure of the stack is given below as an illustration. You will see two blue layers, a red, a yellow-green, and a green layer. The latter is the new layer in the stack.
More information
Would you like to know more about OLED TVs and TV techniques, setting up a television or connecting a television? Then take a look at our tips and advice section .
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