Nowadays, LCD technology in the panel market is facing many challenges, such as AMOLED, Micro LED, laser screen, etc., LCDs are all facing unprecedented pressure. However, it is too early to say that LCD loses its future. After all, the cost of technology has to be considered when entering the market. Today, let's break down the development history of LCD backlight technology, and how LCD can continue to maintain an advantage in the future competition with the blessing of different backlight technologies.
There are three kinds of backlight sources that LCD TVs (Liquid CrystalDisplay) really use for commercialization, namely CCFL (cold cathode fluorescent tube, also known as LCD TV), LED (light emitting diode, also known as LED TV), HCFL (hot cathode fluorescent tube) Among them, HCFL technology is suitable for larger-size TVs and can be applied to products over 66 inches, which is less on the market.
CCFL Cold Cathode Fluorescent Lamp is referred to as CCFL), which is translated as cold cathode fluorescent lamp in Chinese. It has the advantages of high power, high brightness, and low energy consumption. It is widely used in display, lighting and other fields. . This kind of backlight is a light source that excites phosphors by cold cathode gas discharge to emit light. The thin gas containing a small amount of mercury will be ionized under high voltage. The secondary electron emission of the ionized gas will bombard the mercury vapor, so that the mercury vapor is excited and emits ultraviolet rays. The ultraviolet rays excite the phosphor layer coated on the wall tube to make It glows. Its biggest advantage is its high brightness, but its disadvantage is its high power consumption and large volume.
The core technology of the CCFL backlight module is the optical technology of the light guide plate. There are mainly two types of light guide plate forms: printing and injection molding. Others such as injection molding and printing, laser dots, corrosion, etc. account for a small proportion and are not suitable for batches. Production principles. Because of its low cost, printing has become the mainstream technology for a long time in the past, but low qualified products have always been its main disadvantage. LCD products require a more precise light guide structure. Injection molded light guides used to be the mainstream of CCFL backlight development. .
However, since 2012, CCFL monitors have gradually withdrawn from the market.
LED TVs brought by TV manufacturers appeared for the first time at CES in 2009. This year is also known as the "first year of LED TV." The original LED TV only replaced the CCFL backlight with the LED backlight. The biggest difference between the two light source systems of CCFL and LED is that CCFL is a line light source and LED is a point light source. The fluorescent tubes used in CCFL are arranged vertically or horizontally behind the liquid crystal panel, while the LED backlight is arranged behind or around the panel with point-shaped LED light sources.
With the development of time, LED technology is also advancing. LCD backlight requires a white light system, and RGB LEDs can form white light. Such a system is theoretically the best. Because there are three primary colors in the system, the color gamut of the display screen is more powerful. However, the RGB LED backlight system is complicated and the cost is too high, and it is generally only used on high-end LCD displays.
The low-end LCD display uses blue LEDs mixed with yellow phosphors to form white light. There is more blue light in this white light (this is why we often say "blue light hurts the eyes"). The green performance ability is not enough, so the color gamut is relatively weak. This kind of backlight system puts the LED light bar at one end of the display, and then uses the light guide plate to form a surface light source, which is the common WLED backlight.
There used to be a plausible statement that, regardless of the CCFL backlight or the LED backlight, the ultra-thin body and the good color of the screen are a pair of contradictions that are difficult to reconcile. Thinness can only sacrifice image quality and color. Judging from the current machines on the market, this theory is roughly correct, because ultra-thin LED TVs generally use white-light side-mounted LED backlights, so the picture quality effect will inevitably be lost.
This is because according to the different arrangement of LED backlights, LED LCD TVs can be divided into side-mounted LEDs (LED point light sources are distributed around the LCD panel) and direct LEDs (LED point light sources are distributed behind the LCD panel). According to the color of LED backlight, it can be divided into white light LED and three primary color LED (ie RGB-LED). Compared with direct-lit LED backlights, side-mounted LED backlights need to use a light guide plate to transmit light to the back of the liquid crystal panel, which is likely to cause light leakage at the edges of the screen and uneven brightness in the middle of the screen. However, the side-mounted LED backlight also has its own advantages, that is, it can achieve an ultra-thin body. Compared with the RGB-LED backlight, the white LED backlight has a lower cost advantage and lower technical requirements, but the picture color But it is far inferior to RGB-LED backlight.
Currently, LCDs mostly use LED as the backlight source, high-end products use RGBLED, and low-end products often use WLED backlight. LED can replace CCFL successfully because of its long life and strong stability, low working current, so the power consumption is lower than traditional light sources. The energy-saving and durable characteristics of LED combined with its slim size are in line with the current display users' pursuit of ultra-thin and environmentally friendly concepts.
Quantum Dots (Quantum Dots, also known as QLED) is a nano-level material that can emit light. QLED is regarded as the third-generation innovative technology of light-emitting diodes (LED), and manufacturers began to launch them in early 2013. Under the excitation of blue LED, quantum dots with different diameters can emit different pure colors. Quantum dots with a size of 2 nanometers can absorb long-wave red and show blue. Quantum dots with a size of 8 nanometers can absorb short-waves. Blue, showing red. This feature allows quantum dots to change the color of light emitted by the light source. Therefore, these characteristics can be applied in the field of liquid crystal panels.
QLED uses blue LED as the light source, and puts the optical material using quantum dots between the backlight and the LCD panel, so that bright colors can be obtained through red, green, and blue light with sharp peaks; because the quantum dots emit a very narrow spectrum , Its color gamut is higher, can produce richer colors, and the color gamut reaches or exceeds the OLED level. As early as the beginning of 2013, Sony launched the X9000A series of 4K TVs, equipped with Sony's unique Terry Magic Color technology, which is also the world's first 4K TV using quantum dot technology. Terri Charm technology is an innovation in the backlight technology of LCD TVs. Through the control of the color of the backlight by quantum dots, it provides more pure three primary colors. Through the deployment of high-purity three primary colors, it can achieve a wider range than traditional white LEDs. Color gamut. Under the NTSC standard, the color gamut coverage of quantum dot TVs is as high as 110 percent . The color gamut of ordinary LED TVs is only 72 percent , that of high-color gamut TVs is about 96 percent , and the measured color gamut of OLED TVs is 89 percent . And QLED's production cost, technical difficulty, and service life have certain advantages. However, QLED has one of the biggest obstacles. The heavy metal cadmium (Cd) must be used in its production raw materials. This heavy polluting metal is strictly prohibited in the European and American ROHS standards. Some manufacturers have also developed cadmium-free QLED displays, but the display efficiency is greatly reduced, which is the main reason why QLEDs have not become popular.
Mini LED, also known as sub-millimeter light-emitting diode, was first proposed by Epistar, which means LED with a grain size of about 100 microns or more. Mini LED is between traditional LED and Micro LED, in short, it is an improved version of traditional LED backlight.
Micro LED is a new generation of display technology. It is LED miniaturization and matrix technology. In simple terms, it is to thin, miniaturize and array the LED backlight, which can make the LED unit smaller than 100 microns, which can be achieved just like OLED Each picture element is individually addressed and driven to emit light (self-luminous).
Many people tend to confuse Mini LED and Micro LED. In fact, in theory, Mini LED and Micro LED represent two different things.
From the structural principle point of view, Micro LED is simpler, but its biggest problem is the well-known massive transfer. How to make LEDs miniaturized requires wafer-level technology. For example, a 4K-level Micro LED screen requires more than 24.88 million LEDs to be highly integrated.
From the point of view of manufacturing process, Mini LED has higher yield than Micro LED and has special-shaped cutting characteristics. It can also be used with a flexible substrate to achieve a form of high-curved backlight. It adopts a local dimming design and has better color rendering. It can bring finer HDR partitions to the LCD panel, and the thickness is also close to that of OLED, and it has the power saving function.
Mini LED can be regarded as an improved version between traditional LED and Micro LED, based on traditional LED backlight, and can directly deploy RGB three-color LED modules, so that the effect of RGB three primary colors is not missing.
