In recent years, medium to large-sized liquid crystal display (LCD) devices, such as computer screens, LCD TVs, etc., have become increasingly mainstream in the tablet display market. Due to the fact that liquid crystals themselves do not emit light, they need to rely on external light sources, such as backlights, to achieve their display functions. Especially for medium and large-sized liquid crystal displays, it is very important to provide a backlight for all light sources.
LCD backlight is commonly used in two types: cold cathode tubes (CCFLs) and light-emitting diodes (LEDs). Initially, LEDs were mainly used for small and medium-sized LCD displays, such as mobile phones, digital cameras, and PDAs. In the field of medium and large-sized LCD displays, due to high requirements for brightness and heat dissipation, CCFL light sources are traditionally used. With the continuous development of backlight technology, especially the continuous improvement of LED luminous efficiency, and the continuous overcoming of the difficulties and high application costs of large-sized LCD backlight technology, LED backlight is not only widely used in small-sized LCD, but has gradually replaced traditional CCFL in recent years. It has emerged in the backlight field of medium and large-sized LCD displays such as laptops, computer displays, and LCD TVs, and there is a trend to gradually replace CCFL backlight sources. With the increasing awareness of environmental protection and user demands for image quality, solid-state light source LEDs with advantages such as environmental protection, good color reproduction, and long lifespan are favored.
A significant feature of using LED backlighting is energy efficiency. The implementation of national standards for energy conservation and consumption reduction, such as energy consumption level labeling, has made beneficial attempts in this regard for medium and large-sized LCD TV products.
As a new type of flat panel display product, the performance advantage of LCD display devices with LED backlighting is beyond doubt. Especially with advantages such as high display color gamut, bright image quality, energy conservation and environmental protection, and long lifespan, compared to CCFL backlit LCDs, it is easier to achieve a lightweight appearance. Another advantage of using LED backlight is high color saturation, especially for straight down backlit LCDs that use a mixture of three primary or multi-color LED white light, which have excellent display image quality and a wider color range. However, the backlight power consumption of three primary color LEDs is much higher than that of white light LEDs, and there is a price difference of 4-5 times in cost. Currently, considering cost reasons, new backlight LEDs packaged with blue chips and red green fluorescent powder are mostly used to replace three primary color LEDs. In this case, the color saturation of liquid crystal displays can be in the range of 72% to 85% of the NTSC standard, and they have better color rendering quality than CCFL backlight LCDs at low cost.

The Development of LED Backlight Technology
Structurally, liquid crystal backlight mainly adopts two types of structures: side light type and straight down type. At present, the liquid crystal display market is developing towards thinness, often using side light structures to achieve ultra-thin design. In 2009, Samsung launched an ultra-thin LCD TV with side lit LED backlight, and since then, LED side backlight has been widely used as a new technology in large-sized LCD displays. The side lit backlight structure places the LED light source on the side, which can significantly save space and make it easier to achieve lightness and thinness. But when the light source enters from the side, the requirements for the design of LED strips and light guide plates have also been raised to achieve uniform light output from the front. At the same time, the side backlight structure cannot use three primary color LED light sources to mix white light, and local dynamic backlight control technology, which results in inferior color reproduction performance and contrast of LCD displays.
For large-sized LCD displays, especially those that require high color display quality and high brightness performance, the uniformity and brightness of the side light backlight source are limited, and the cost and processing difficulty of the light guide plate also increase. Therefore, a straight down backlight structure is often used, which has a relatively simple manufacturing process and does not require a light guide plate. The key technology lies in color and brightness uniformity, and is currently the mainstream in the development of large-sized backlight sources. Especially for backlights using high color rendering index white LED light sources, compared to side lit backlights, the number of LEDs used at the same brightness is less, the layout is not too dense to facilitate heat dissipation, and it is also easier to achieve uniform light output.
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