LED are made by replacing CCFL cold cathode fluorescent tubes with light-emitting diodes to achieve a better lighting display. However, LED backlighting has evolved since then, so it is used for three main types, with different display effects.



                                       



  • a. Direct down LED backlight.


The main feature is that the backlight panel is covered with LEDs for uniform illumination. Characterized by the fine picture quality, the backlighting can be set in areas, that is, the so-called "local control of light" technology, so as to achieve individual processing for different colors. However, this backlighting technology will affect the thickness of the TV, so some ultra-thin TVs as a selling point to another backlighting technology.


As shown in figure (a), straight down type backlighting process is simple, no light guide plate, LED array placed at the bottom of the lightbox, the light emitted from the LED through the bottom and side reflection, and then through the surface of the diffusion plate and optical module uniformly emitted. The thickness of the backlight is determined by the distance between the bottom of the lightbox and the scattering plate, usually the thicker the thickness, the better the light uniformity of the backlight. The type of LED light field distribution plays an important role in the color and brightness uniformity of the backlighting, the LED lights used in the backlighting usually have the Lambert type and side emission type two kinds, because the side emission type LED is more conducive to the light uniformity of the backlighting, direct down type backlighting mostly use side emission type LED. However, large-angle side emission LED due to its low light intensity in the middle, easy to cause dark spots, affecting the uniformity of the backlighting.


  • b. Side entry type LED backlight.


It is very easy to understand that side entry LED backlighting is the illumination of the LCD panel by erecting LED bulbs around the panel and shining them into the light guide. Because there are fewer bulbs, so run TV manufacturers will run TV body design thinner and light, the mainstream ultra-thin TVs on the market are using this technology. However, due to some inherent defects, can not achieve local control of light, color performance is not as good as the direct type.


As shown in figure (b), side light type backlight module will be a point light source set in the special design of the light guide plate side as a backlight source, using fewer LEDs; and because the light source is placed on the side of the light guide plate, LED by the number and brightness restrictions, still need to disperse the light evenly throughout the plane, will form when the panel area is larger, the more limited the use of light source glow. Because the LED backlight on the side of the product, so the back only need to add a light guide can be the appearance of the thickness of liquid crystal products can be very thin, such as Sony's ZX1 series, it is the use of sidelight type backlight module.


  • c. Quantum dot technology.


Recently very popular "quantum dot TV", in fact, is also a new type of backlight technology. It is characterized by the use of nano-crystalline material instead of an LED light source, to achieve a purer, more realistic color reproduction of the backlight color, the color effect of the LCD TV to enhance the level of comparable to OLED. Therefore, the use of quantum dot technology LCD TVs, but also the best display effect in the market, the most expensive.


Quantum dot technology is a new way to improve the color gamut. Quantum dots are composed of zinc, cadmium, selenium, and sulfur atoms and are nanomaterials with crystal diameters between 2 and 10 nanometers. Due to its unique optoelectronic properties, it emits very pure, high-quality monochromatic light of various colors when stimulated by optoelectronic stimuli, depending on the diameter of the quantum dots. Based on this property, if the quantum dot material is used in the backlighting of a TV, irradiation with a blue LED can emit a full spectrum of light, thus finely adjusting the backlight, thus significantly improving the color gamut performance and making the colors more vivid.


As shown in Figure (c), it can be seen that quantum dot technology also requires blue LED excitation, further proving the importance of the blue LED invention. Quantum dot backlighting is not complicated, the quantum dots are made into a thin film and placed between the blue LED and the LCD panel, which can effectively improve the color gamut of the LCD panel. The quantum dots themselves are very small in size, so the thickness of the quantum dot film can also be controlled without increasing the thickness of the LCD device.

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LED backlight technology