LCD vs OLED

LCD vs OLED – Spray Protective Film – Ultrasonic Atomizer – Cheersonic

The following article comes from the hardware notebook, the author snail

To understand how the screen works, you must first understand what a pixel is. The whole picture you see is actually made up of countless small dots, and these small dots are what we call pixels. Each pixel is composed of three sub-pixels of red, green and blue. Red, green and blue are the three primary colors. You can get all the colors you want through the color ratio of the three sub-pixels of red, green and blue, so that each pixel performs its own function to display its own color, and finally piece together the complete picture you see. screen. Resolution refers to the number of pixels contained within a unit length.

1. How LCD and OLED work

1.1, LCD working principle

The cross-sectional view of the LCD is as follows, there are mainly 7 layers, from bottom to top are the backlight layer, vertical polarizer, positive circuit, liquid crystal layer, negative circuit, horizontal polarizer and color filter.

The function of the bottom backlight layer is to emit white light, and the white light can become light of the corresponding color after passing through the color filter with a color. Note that the backlight layer is not an independent LED lamp bead under the pixel, but all pixels of the entire screen share a large backlight layer.

When we apply a voltage to the positive circuit, it will penetrate the liquid crystal layer and connect the negative circuit to form a loop. This voltage will drive the liquid crystal layer to deflect. At this time, the liquid crystal layer will block a part of the light just like the blinds. At this time, we only need to control The magnitude of the voltage can control the deflection angle of the liquid crystal molecules, thereby controlling the brightness of the red, green and blue sub-pixels. By changing the brightness ratio, you can mix all the colors you want.

1.2, OLED working principle

The full name of OLED is organic light-emitting diode (organic Light-Emitting Diode), and it also has three sub-pixels like the LED screen. The difference is that it does not have a liquid crystal layer and a backlight layer, and it is a specially designed self-luminous diode. By controlling the voltage, thereby controlling the current flowing through the diode to change the brightness, you can control the color ratio of each sub-pixel, and finally mix the color you want.

OLED does not have a backlight layer, and each pixel can be independently controlled on/off, so it does not need to be turned on like an LCD screen, and the entire backlight layer needs to be lit. Each pixel of the OLED screen can be understood as an independently controlled lamp bead, which can be used as a screen reminder. When the phone is locked, some pixels can be individually lit to display time and notifications with low brightness and low refresh rate. Wait for some important information.

2. Comparison of the pros and cons of LCD and OLED

2.1, OLED lower power consumption

As long as the LCD screen is turned on and the entire screen is fully bright, it will continue to consume power. Only when the OLED screen is turned on to display a pure white screen, the power consumption will be higher than that of the LCD, but each pixel of the OLED screen controls the brightness and switch independently, so that the brightness can be reduced or even turned off. So unless you’re stuck in a white screen for a long time, OLED will last longer.

2.2, OLED has higher contrast ratio
Contrast refers to the ratio of brightness between black and white on the screen. The higher the contrast, the more vivid the picture and the more intense the color.

If the LCD is to display pure black, the ideal state is that the liquid crystal molecules are completely closed to completely block the emitted backlight, but the deflection of the liquid crystal molecules cannot be completely closed. Therefore, when displaying black, there will be a small amount of white light shining out, so what you see on the screen is not pure black, but a gray with greatly decreasing brightness. This feature determines that the LCD cannot display black in the true sense of pure black. .

OLED itself does not have a backlight, and each pixel is independently controlled, so the power supply to display black pixels can be directly cut off, so that no light is emitted at all, and pure black in the true sense can be achieved.

Therefore, the contrast ratio of the OLED screen is higher.

2.3. OLED has faster response time and more advantages in dynamic display.

When displaying a dynamic picture, it means that each pixel needs to switch colors quickly, and the color switching takes a certain amount of time. This time is what we call the screen response time.

If the response time is too long, when the dynamic picture is displayed, the pixels will not have time to change the color, so that the previous picture has not completely disappeared, and the next picture will be displayed, which will lead to afterimages on the screen.

The color switching of the LCD screen is accomplished by controlling the deflection of the liquid crystal molecules. Therefore, the deflection speed of the liquid crystal layer directly determines the grayscale response time of the LCD, and the deflection of the liquid crystal layer is related to the temperature.

The OLED screen does not have a liquid crystal layer and is naturally not limited by the temperature of the liquid crystal layer. However, the OLED screen does not have no response time. The OLED screen switches colors between colors. The response time is very short and there is almost no smear. However, the OLED screen switches from pure black to pure white, or from pure white to pure black. It will take a lot longer than other colors, but OLED also takes less time to switch between black and white than most LCDs.

Therefore, OLED has a natural advantage in displaying dynamic pictures on the screen.

2.4. OLED can be made thinner and easier to fold

The OLED screen does not have a backlight layer and a liquid crystal layer, so it is very easy to make thin, and can be bent as much as paper. Being able to bend means that a curved screen can be easily realized, which can significantly improve the texture of the phone itself.

In addition to the backlight layer and the liquid crystal layer, the LCD screen also has some polarizers in the middle, so it is much thicker than the OLED. The backlight layer and the liquid crystal layer are hard substrates that can only be bent very slightly, and can only be seen on large panels such as desktop monitors.

2.5. OLED has a shorter lifespan

LCD uses the backlight layer to emit light. The liquid crystal layer is only responsible for deflecting and controlling the amount of light emitted. The filter layer is only responsible for changing the color of the light and does not participate in the light emission. The voltage is applied to the liquid crystal layer that does not participate in the light emission.

The OLED screen voltage is directly applied to the self-luminous diode, resulting in frequent migration of electrons in the light-emitting layer of the OLED. In addition, the light-emitting layer itself is an organic substance, and organic substances are very easy to age compared to inorganic substances, so organic substances + frequent electron migration + self-luminescence directly lead to the screen life of OLED is significantly shorter than that of LCD screen.

2.6, LCD has the disadvantage of light leakage

Since the LCD screen has a backlight layer, and the screen panel is eventually installed on a mobile phone or a monitor, the backlight of the backlight layer can easily leak out at the connection between the screen borders. When a pure black screen is displayed, the border will appear. Large area halo phenomenon, this is called light leakage.

2.7. OLED is prone to screen burn-in

The backlight of the LCD screen is a whole piece, and all the pixels will age together. Each pixel of the OLED screen emits light independently, which means that different areas of the screen have different aging speeds depending on the degree of use.

For example, if the area A shows blue for a long time, the blue pixels decay faster. The next time a solid color is displayed, the blue in that place will be slightly darker, resulting in an afterimage, as if the picture was burned on the screen. This phenomenon is called screen burn-in. It’s not that the physical level of the screen is burnt, but the color difference of the screen caused by uneven pixel aging.

2.8, LCD and OLED all hurt the eyes, but there are differences.

The brightness of the mobile phone screen needs to be controllable, otherwise it cannot match the ambient light intensity. At present, there are two main ways to control the brightness: PWM and DC adjustment.

DC dimming is very simple, directly control the voltage to change the brightness of the lamp, the higher the voltage, the brighter the brightness. Since the DC dimming light source is always on, there is no stroboscopic eye injury.

PWM dimming is to adjust the duty cycle to adjust the brightness of the control lamp. The larger the duty cycle, the brighter the brightness. Its dimming control lamp switching time will produce stroboscopic, so it has a disadvantage of hurting the eyes. The higher the frequency, the less obvious the stroboscopic phenomenon.

Due to the characteristics of the OLED screen, if DC dimming is used, when the brightness is too low and the voltage is too low, the screen will have the same uneven effect as a rag, which has a particularly great impact on the display screen, so the OLED screen cannot use DC. For dimming, only PWM can be used.

Because OLEDs are easy to age due to organic materials, OLEDs cannot use high-frequency PWM dimming, but can only use low-frequency PWM dimming. The general frequency is about 250Hz at the highest, and some people with sensitive vision will notice it, which is more prone to visual fatigue.

The most harmful part of the light emitted by the screen to the human eye is the blue light with wavelengths of 420-440. These high-energy light will cause irreversible damage to the human retina. The backlight of the traditional LCD screen uses several high-brightness LED lamp beads plus a uniform light plate. Completed, a considerable part of the high-energy blue light emitted by these LED lamp beads is in this range.

The strong blue light of LCD hurts the eyes, and the PWM dimming of OLEDs also hurts the eyes. Some low-end screens also use PWM dimming on the LCD in order to save costs. Which one does more damage is hard to say.

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.