Do you think LCD will be replaced by OLED in the near future?

09-05-2020

As we all know, LCD is the liquid crystal display technology. Its history can be traced back to more than 20 years ago, and it is widely used in electronic devices such as televisions, computers, and smart phones. In recent years, the phones of manufacturers are basically equipped with OLED screens. However, the voice of the mobile phone industry about "LCD is never slave" is still in the air.

Why?Let's first learn the light emitting principle of LCD and OLED.

In fact, whether it is LCD or OLED, they are currently the two most used display technologies in the field of smart phones, and screens including TFT LCD, IPS, AMOLED display, PMOLED display, etc. are "enhanced versions" based on these two technologies. .

tft lcd display screen

*The picture above shows the types of LCD and OLED screens.

 

The structure of the LCD screen is like sandwiching a liquid crystal layer between two "glasses", a thin film transistor is placed on the lower substrate, and a color filter layer is placed on the upper substrate. The liquid crystal layer in the middle will produce different light under the effect of voltage Characteristics, when the final projection, it passes through the color filter layer to produce different colors.

OLED stands for Organic Light Emitting Diode. It is recognized as the successor of LCD. It is also considered by the outside world as the best solution for the next-generation smart phone display.

Unlike LCD, each pixel of OLED can emit light independently. We can think of each sub-pixel of it as an LED lamp, which is composed of three sub-pixels of red, green and blue, and an array of these pixels It is the OLED panel.

To understand it simply, the light source layer and the display layer of the LCD are separated, and the OLED display layer and the light source layer are combined into one. At the same time, the light source of the LCD is fixed and cannot emit light alone.

The structure of OLED has brought many bonus features, including but not limited to:

A)      The display efficiency of OLED is higher than that of LCD that requires multi-level "filtering" of light;

B)      OLED no longer needs a backlight, the screen can be made thinner;

C)      By cooperating with different substrate materials, OLED also realizes the display effect of bending or even folding.

 

Beyond this, OLED display technology can offer power-saving advantages over LCDs, which is important, especially for battery-powered applications such as mobile phones. An OLED’s power consumption will vary with image content and brightness, as light is generated only at the individual pixels needed to display the image. A dark image or a graphic on a black background will consume much less power than bright images or graphics. In contrast, LCD backlights must be ON while the display operates. It’s possible to control individual zones of the backlight separately to save power, but this added complexity is usually only applied in larger displays.

OLEDs can achieve a much higher contrast ratio if reflections from the front surface are carefully controlled. If no current flows through an OLED pixel, it does not emit any light. In contrast the shutter effect of an LCD pixel does not block 100% of the light. Depending on the specific LCD technology used and the angle of observation, a small percentage of the light generated in the backlight can escape. This can wash out dark areas of an image. It is possible but expensive to limit this light leakage to a point where the contrast of an LCD and OLED display become perceptually equivalent.

RGB OLEDs naturally generate a narrow bandwidth of light. This leads to very saturated primary colors and a wide color gamut. This enables OLED technology to display colors which are not easily accessible to LCDs unless RGB backlights or quantum dot phosphors are used for the illumination. Often OLED colors are used “as is”, however, for very high image color fidelity, such high color saturation needs to be electronically ‘tuned down’, to match the color bandwidth of the rendering chain.

It stands to reason that OLED has unlimited potential for the future development trend of the mobile phone market. But compared with LCD display, it also has the widely criticized shortcomings, including screen burning and stroboscopic problems.

As we have seen above, each pixel of the OLED will emit light by itself, and the brightness control is driven by current, which controls the light-emitting material to form different colors, that is, DC dimming.

However, due to the different materials of the pixels of different colors, the life of their luminescence will be affected to some extent; coupled with the difference in the wavelength of the three-color sub-pixels, they also have different requirements for current, such as blue requires higher current through . Therefore, in the case of excessive screen loss or low brightness, it is very difficult to control the brightness ratio of each sub-pixel. At this time, the OLED screen may turn red, or "after-images" appear when displaying content. This is what people often call "burning the screen".

In order to solve this technical problem, manufacturers have come up with a new method-using PWM dimming to replace the previous DC dimming. The specific operation of this method is to make the screen blink continuously. After reaching a certain frequency, it will give the human eye a temporary visual effect and make the screen look "steady bright". If you need to reduce the brightness, you only need to increase the interval between flashes.

In this way, PWM dimming led to the appearance of stroboscopic phenomenon, and was criticized by the "LCD Party".

 

LCD was first proposed in 1968. During its development process, the technology has gradually overcome its own shortcomings and defeated other technologies. What are its remaining flaws? It is widely recognized that LCD is very hard to be made flexible. In addition, LCD does not emit light, so a back light is needed. The trend for display technologies is of course towards lighter and thinner (screen).

But currently, LCD is very mature and economic. It far surpasses OLED, and its picture quality and display contrast do not lag behind. Currently, LCD technology's main target is head-mounted display (HMD), which means we must work on display resolution. In addition, OLED currently is only appropriate for medium and small-sized screens, but large screen has to rely on LCD.

LCDs offer an advantage over OLEDs in applications where a continuous static image is required. The light emitting materials (also called phosphors) in OLEDs are affected by luminance decay as a function of the total amount of current that has passed through the pixel. This decay differs for red, green and blue phosphors. The dimming effect is subtle, but when adjacent pixels are illuminated at the same time it can become noticeable as an undesired brightness variation or color shift. LCDs don’t suffer from this dimming effect, which makes them a more suitable solution for applications with static images or images with static elements.

 

While deeply impacted by OLED’s super thin and flexible display, we also need to analyse the insufficiency of OLED. With lighting material being organic, its display life might be shorter. LCD can easily be used for 100 000 hours. The other defense effort by LCD is to develop flexible screen to counterattack the flexible display of OLED. But it is true that big worries exist in LCD industry.

LCD industry can also try other (counterattacking) strategies. We are advantageous in large-sized screen, but how about six or seven years later? While in the short term, OLED can hardly compete with LCD in large size screen, how about that people may change their use habit to give up large screen? People may not watch TV and only takes portable screens.

Some experts working at a market survey institute CCID (China Center for Information Industry Development) predicted that in five to six years, OLED will be very influential in small and medium-sized screen. Similarly, a top executive of BOE Technology said that after five to six years, OLED will counterweigh or even surpass LCD in smaller sizes, but to catch up with LCD, it may need 10 to 15 years.


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