Which is better, LCD or LED?
1. Advantages of OLED:
(1) Always-on display
In the principle section above, we specifically mentioned that all pixels of LCD screens share a large backlight layer, while each pixel of OLED screens can be independently controlled to turn on and off. Therefore, the first advantage of OLED screens can be seen here, which is that they can realize always-on display. As we all know, many mobile phones can display the battery level, time, notifications or some other customized information of the mobile phone at a lower power consumption when the screen is off. Many manufacturers use always-on display as a selling point of mobile phones. Obviously, this function cannot be achieved by LCD, because if the LCD screen wants to display content, the entire backlight layer needs to be turned on.
(2) Bright pictures brought by high contrast
Contrast refers to the ratio between the brightest white and the darkest black in the light and dark areas of an image. Generally, the higher the contrast, the brighter the picture looks and the richer the color.
If the LCD screen wants to display black, according to the above principle, in an ideal state, the liquid crystal molecules of the red, green and blue sub-pixels need to be completely closed to completely block the white light emitted by the backlight layer. However, in reality, the liquid crystal molecules cannot be completely closed, and part of the white light emitted by the backlight layer will leak out. Therefore, the final black display effect on the LCD screen is not pure black, but gray with greatly reduced brightness.
The principle of OLED screens is to emit light of corresponding colors by electrifying organic self-luminous materials, and there is no backlight layer. Therefore, when it is necessary to display black, as long as the power supply of the pixel is completely cut off, it can be completely non-luminous, thus displaying true pure black. In this sense, we can think that the contrast of OLED screens is close to infinite, and the high contrast will also make the display effect of OLED screens significantly stronger than that of LCD screens.
(3) Light leakage problem
LCD screens have a whole large backlight layer. When assembling, the white light of the backlight layer will easily leak out at the junction of the screen and the frame, and a large area of halo will appear near the frame. This is what we call light leakage. Since OLED screens do not have a backlight layer, the light leakage problem is fundamentally solved.
(4) Screen response time caused by ghosting
When we display dynamic images, the color displayed by each pixel needs to switch quickly, and it takes a certain amount of time for the pixel to switch from one color to another. This time is the so-called screen response time. If the response time is too long, the color of the pixel will not switch in time when displaying dynamic images, and the previous frame of the picture has not completely disappeared, leaving a residual image on the screen.
The color switching of the LCD screen is completed by the deflection of the liquid crystal molecules. Therefore, the deflection speed of the liquid crystal layer directly determines the response time of the LCD screen. The deflection speed of the liquid crystal molecules is greatly affected by the temperature. The lower the temperature, the slower the deflection. This is why there will be serious ghosting on the outdoor LCD screen in winter.
When the OLED screen switches colors, there is no deflection problem of liquid crystal molecules, and it will not be affected by the external temperature. Therefore, the response time of the OLED screen is often much shorter than that of the LCD screen. It can be said that the OLED screen has a natural advantage when displaying dynamic images.
(5) Superior physical properties
The OLED screen does not require the complex multi-layer structure of the LCD screen, so it can be made thin. On the other hand, OLED screens can be bent at a larger angle. Therefore, with the development of OLED screens in recent years, various curved screens and folding screen mobile phones have become popular. We will not discuss the practicality of these technologies here. From the perspective of technical implementation, OLED screens provide more possibilities for various designs.
On the other hand, since OLED screens do not require the entire backlight layer to light up at the same time, they are also significantly better than LCD screens in terms of power consumption.
2. Advantages of LCD screens
Having said so many advantages of OLED, is LCD really useless? Obviously not. The advantages of OLED screens are obvious, but they also have very extreme disadvantages. As a result, some users are still unwilling to give up LCD screens until now.
(1) Service life
In recent years, we often hear the word "burn-in". It does not actually mean that the screen is burned or damaged, but a display distortion phenomenon caused by the aging of OLED screens.
As mentioned earlier, the principle of OLED screens is that organic self-luminous materials emit light when electricity is applied. High school chemistry knowledge tells us that organic matter is more prone to aging and property changes than inorganic matter. Due to frequent electron migration, the color of the organic self-luminous material of OLED screens will gradually change. Since different areas of the screen are used at different frequencies, the aging speed of different areas of the OLED screen will be different. When displaying pure color content, the areas with a deeper degree of aging will have residual images. For example, if the battery display area displays the battery icon for a long time, if it displays a pure color again, a battery-shaped residual image will be left. This is the so-called "burn-in".
However, since the luminous part of the LCD screen is the entire backlight layer, even if different areas of the screen age, the aging degree is the same. Although there will be overall color difference, there will be no "burn-in" phenomenon caused by different degrees of aging.
(2) Visual damage caused by dimming method
When we use the screen, we need to adjust the brightness of the screen according to the ambient light conditions. There are currently two mainstream dimming methods, namely DC dimming and PWM dimming.
DC dimming: The brightness of the screen is adjusted by changing the voltage or current supplied to the screen.
PWM dimming: Pulse width modulation (PWM), through the "screen on-off-screen on-off" such a continuous alternation of light and dark, and the human eye has a visual retention effect, about 1/16 seconds, during which the effect seen by the human eye will remain, PWM uses this principle to continuously dim, and the frequency of PWM dimming refers to the speed of screen on-off.
There is no problem with LCD screens using DC dimming, but due to its display principle, if OLED screens use DC dimming, the screen display color will be uneven when the brightness is low, which is what we call "rag screen". Therefore, most OLED screens on the market currently use PWM dimming. If the frequency of PWM dimming is low, the screen will produce stroboscopic light, causing vision damage. This is why many people who are used to LCD screens feel eye pain and tears when they first use OLED screens, which leads to the saying that OLED is a "blind screen".
In fact, high-frequency PWM dimming can effectively solve the problem of stroboscopic light, but due to technical and cost limitations, many OLED screens on the market currently still use low-frequency PWM dimming.
(3) LCD screen segmentation (IPS, TN and VA screens)
IPS, TN and VA on computers and TVs are all LCD screens. The difference between them is the different structures of the liquid crystal layer. TN can achieve a very fast deflection speed but the color is relatively poor. VA can achieve a very high contrast but the response speed is very slow. Although the contrast of IPS is not as high as that of VA, the color is also good. The response time is between VA and TN, which is relatively moderate. Therefore, the overall experience of IPS is the best. This is why it is recommended to buy a screen with an IPS panel when buying a computer.
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