Analysis of LED TV energy-saving technology from concept to popularization

With the rapid development of liquid crystal display technology, various cutting-edge display technologies have been widely used in the field of LCD TVs. Looking at the development of liquid crystal display technology in the past two years, the birth of LED backlight technology is undoubtedly a major breakthrough in LCD TV technology. LED has become one of the hottest keywords in the past two years due to its excellent features such as energy saving and environmental protection, outstanding picture quality and color, and lightness.

As a new display technology, LED has been popularized and applied in other fields for a long time. However, due to its high cost and difficulty, it has not been widely used and popularized in the field of LCD TVs, and has always been regarded as a conceptual product by consumers. However, after several years of research and development and actual application, this bottleneck was completely broken in 2009, which not only controlled the cost of the whole machine to the lowest, but also allowed consumers to experience the visual impact brought by the new display technology.

From the initial concept product to the current popular product, LED TV has won the favor of the majority of consumers. As LED energy-saving TVs become popular, we might as well take a new look at the latest LED energy-saving technology, so that everyone can have a deeper understanding of LED TVs and be more targeted when choosing.

Basic technical principles of LED

LED (Lighy Emitting Diode), also known as light-emitting diode, uses solid semiconductor chips as light-emitting materials. When a forward voltage is applied to both ends, the carriers in the semiconductor recombine, releasing excess energy and causing photon emission to produce visible light.

The LED light-emitting process includes three parts: carrier injection under forward bias, recombination radiation, and light energy transmission. Tiny semiconductor chips are encapsulated in clean epoxy resin. When electrons pass through the chip, negatively charged electrons move to the positively charged hole area and recombine with it. Electrons and holes disappear and photons are generated. The greater the energy (band gap) between electrons and holes, the higher the energy of the generated photons. The energy of photons in turn corresponds to the color of light. In the visible light spectrum, blue light and purple light carry the most energy, while orange light and red light carry the least energy. Because different materials have different band gaps, they can emit light of different colors.

To use an analogy, LED is like a hamburger, the luminous material is the "patty" in the sandwich, and the upper and lower electrodes are the bread that sandwiches the meat. Through the research on the luminous materials, people have gradually developed LED components with various light colors and higher and higher light efficiency. However, no matter how they change, the overall luminous principle and structure of LED have not changed much.

The mainstream of LED lighting sources will be high-brightness white LEDs. Currently, most commercialized white LEDs are two-wavelength, that is, a mixture of blue light single chip and YAG yellow phosphor to produce white light. In the future, the more promising white LED is a three-wavelength white LED, that is, an inorganic ultraviolet chip plus red, blue and green three-color phosphor to produce white light, which will replace the fluorescent lamp, compact energy-saving fluorescent bulb and LED backlight market.

Characteristics of different LED technology types

Due to the excellent light-emitting characteristics of LED, the color saturation is better, the response time is extremely fast, and the light leakage effect is weak. By increasing the contrast and performing regional control, the performance is much better than that of cold cathode fluorescent lamps (CCFL). Moreover, cold cathode fluorescent lamps contain harmful substances such as mercury, and LEDs are more environmentally friendly in comparison.

At present, the application of LED technology in the liquid crystal field mainly uses LED light-emitting elements to replace the previous CCFL fluorescent lamp light source as the backlight source of liquid crystal display devices. According to the color of the light source emitted by the LED, it is divided into white light LED backlight source and RGB-LED backlight source.

The goal of emitting white light has been achieved in the color of the light source emitted by the LED. In the imaging principle of the liquid crystal display device, the white light emitted by the backlight passes through the liquid crystal layer and then through the R/G/B color filter film to become an independent primary color. In this process, the key to determining the final color of the liquid crystal display device is not the liquid crystal layer, but the luminous quality of the backlight source. The higher the purity of each RGB primary color light in the spectrum of the backlight source, the purer the primary color can be restored in the end. Only by restoring the pure RGB three primary colors can a pure and true color effect be deployed.

The use of white light LEDs can also effectively reduce the thickness of the LCD panel and achieve ultra-thin products. In LCD display devices, the shape and size of the LED backlight panel will be designed according to the shape and size of the LCD panel. The LED backlight panel is basically rectangular or long. It has two basic structures: side-emitting and bottom-emitting. The side-emitting structure is mainly used for narrow and long strip-shaped backlight panels (generally the length is greater than 2 times the height); while the bottom-emitting structure is mainly used for backlight panels with similar length and width. When the LED is lit, the light enters the transparent organic glass, so that the entire luminous surface can be seen. This is called the edge light effect. The top of the organic glass is made into micro-beads, which can make the light on the entire luminous surface more uniform. There is a layer of milky white transparent plastic film on the top of the organic glass, which can make the emitted light softer. The two sides of the backlight panel are sealed with silver light-shielding tape. Each LED light-emitting unit has two diodes in series, and several columns form an LED array (depending on the length of the backlight panel).

As we mentioned above, in addition to white light, LED also has a backlight technology that can emit three monochromatic lights: R/G/B. Since the three primary colors RGB can be used to mix any color in nature, they are also widely used in LCD TVs.

RGB-LED backlight uses LED components that can emit high-purity red, green, and blue light to achieve a wide color gamut that traditional CCFL light sources cannot achieve. The current mainstream RGB-LED backlight can already reach 105% of the NTSC color gamut, and as long as more powerful LED devices are used, more than 120% of the NTSC color gamut can be achieved. This will be a very effective means of improving image quality for TV sets that mainly restore images.

In addition to better color gamut expression, RGB-LED backlight can also effectively improve the contrast of TV sets, achieving more accurate color levels and a more layered picture. Since the entire backlight source is composed of many tiny LED light-emitting units, it is possible to achieve precise brightness control for each of the light-emitting devices. It becomes possible to correct the brightness of light in a small area according to the characteristics of the original picture. For example, in a picture with strong light-dark contrast, the LED backlight in the dark area can be completely turned off, while the LED backlight in the bright area can achieve high brightness output. The contrast enhancement effect brought about by this will be unmatched by LCD TVs that used to use CCFL light sources.