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Back Light

Backlight is a form of lighting in the electronics industry and is often used for LCD displays. The difference between the backlight type and the front light type is that the backlight is illuminated from the side or the back, while the front light is illuminated from the front as the name implies. They are used to increase the illuminance in a low-light environment and the brightness of computer monitors and Liquid Crystal screens to generate light in a similar way to CRT displays.

In the electronics industry, the backlight is a form of lighting that is often used for LCD displays. The difference between the backlight type and the front light type is that the backlight is illuminated from the side or the back, while the front light is illuminated from the front as the name implies. They are used to increase the illuminance in a low-light environment and the brightness of computer monitors and Liquid Crystal screens to generate light in a similar way to CRT displays.

The light source may be incandescent bulbs, electro-optical panels (ELP), light-emitting diodes (LED), cold cathode tubes (CCFL), etc. Electro-optical panels provide uniform light across the entire surface, while other backlight modules use diffusers to provide uniform light from uneven light sources.
The backlight can be any color. Monochrome liquid crystals usually have backlights such as yellow, green, blue, and white. The color display uses white light because it covers the most color light.
LED backlights are used in small, inexpensive LCD panels. Its light is usually colored, although white backlighting has become more and more common. Electro-optical panels are often used in large displays, and uniform backlighting is very important at this time. The electro-optical panel needs to be driven by high-voltage alternating current, which is provided by the inverter circuit. Cold cathode tubes are used in computer monitors such as computer monitors. The color is usually white. This also requires inverters and diffusers. Incandescent backlight is used when high brightness is required, but its disadvantage is that the life of the incandescent bulb is quite limited, and it generates a lot of heat.
LED backlight can improve the color performance of LCD display. The LED light is generated by three separate LEDs, which provide a color spectrum that matches the color spectrum of the LCD pixel color filter.

Backlit display
Backlight display refers to whether the display screen on the fuselage can emit backlight when the user uses the electronic device, so that the content can be displayed more clearly. Most electronic devices have a backlight display as long as they have a display screen. As long as there is a subtitle display, the backlight is considered normal. Backlight display technology has begun to be applied in the field of LED lighting to provide uniform light sources, which is a new application of backlight technology in the field of lighting.

CCFL (Cold Cathode Fluorescent Lamp) backlight is the most important backlight product for LCD TVs. Cold Cathode Fluorescent Lamp, namely CCFL (Cold Cathode Fluorescent Lamp), or CCFT (Cold Cathode Fluorescent Tube). Its working principle is that when a high voltage is applied to both ends of the lamp tube, a small number of electrons in the lamp tube hit the electrode at a high speed to produce secondary electron emission and start to discharge. After the mercury or inert gas in the tube is impacted by the electrons, the excitation radiation is 253.7nm The generated ultraviolet light excites the phosphor coated on the inner wall of the tube to generate visible light. The life of CCFL tube is generally defined as: at an ambient temperature of 25°C, the tube is driven with a rated current, and the length of working time when the brightness is reduced to 50% of the initial brightness is the tube life. The nominal life of the LCD TV backlight can reach 60,000 hours. CCFL (cold cathode fluorescent lamp) backlight is characterized by low cost, but its color performance is not as good as LED backlight.

LCD backlight
The biggest difference between liquid crystal and plasma is that liquid crystal must rely on a passive light source, while plasma TV is an active light-emitting display device. The mainstream LCD backlight technology on the market includes LED (Light Emitting Diode) and CCFL (Cold Cathode Fluorescent Lamp).

LED backlight uses light-emitting diodes as the backlight source, which is the most promising technology to replace traditional cold cathode fluorescent tubes in the future. Light-emitting diodes are made of several thin layers of doped semiconductor materials. One layer has excess electrons, and the other layer lacks electrons to form positively charged holes. When current passes through, electrons and holes combine with each other. The energy is released in the form of light radiation. By using different semiconductor materials, light-emitting diodes with different light-emitting characteristics can be obtained. The light-emitting diodes that have been put into commercial applications can provide colors such as red, green, blue, cyan, orange, amber, and white. White LED backlights are mainly used on mobile phones, while the LED backlights used on LCD TVs can be white or red, green and blue. In high-end products, multi-color LED backlights can also be used to further improve the color. Expressive, such as six primary colors LED backlight light source. The advantage of using LED backlight is that the thickness is thinner, about 5 cm, the color gamut is also very wide, which can reach 105% of the NTSC color gamut, and the black luminous flux can be reduced to 0.05 lumens, which in turn makes the LCD TV Contrast as high as 10000:1 . At the same time, the LED backlight light source also has a life span of 100,000 hours. The main problem that restricts the development of LED backlight is cost. Because the price is much higher than that of cold fluorescent tube light source, LED backlight light source can only appear in high-end LCD TVs abroad.

Because of the high cost of LED backlights, a manufacturer has introduced improved CCFL (cold cathode fluorescent lamp) backlight LCD TV products, the representative ones being Sony and Sharp. Sony’s wide color gamut cold cathode backlight tube (WCG CCFL) enhances the purity of green by adding phosphor to the silver light of ordinary cold cathode backlight tube, which makes the color gamut wider. The most prominent thing is that the greenness of the TV is quite dazzling. . However, the disadvantage is that the high cost of investment is not acceptable to ordinary families. Some Samsung products also have this technology. And Sharp chose a low-cost idea. Sharp’s eighth-generation panel products use four-wavelength backlight technology (previously used in 65-inch products). The principle of Sharp’s four-wavelength backlight is to enhance the expression of red by adding red LED light-emitting diodes between the tubes. The cost of red LED light-emitting diodes is very low, this trick is more clever than Sony. This also makes it obvious that Sharp’s panel will be reddish in a completely black state!

Backlight life
The liquid crystal of an LCD TV does not emit light, and it is a backlight type display device. There is a backlight on the back of the LCD screen. The LCD TV relies on evenly arranged fine liquid crystal particles on the screen to “block” and “turn on” the light emitted by the backlight to restore the picture. It can be found that as long as the LCD is connected to the power supply, the backlight is working, even if the displayed picture is a black picture, the backlight is also working, that is, the backlight of the LCD TV is always on. After power on, the backlight will light up. If all the LCD pixels on the screen are “turned on”, the backlight will enter the human eye without any obstruction, and the screen will be completely white at this time. When displaying an image, after calculating the on-off state of each pixel through the AD conversion of the display signal, the signal is directly driven to the specific pixel to control the “on-off” of the liquid crystal pixel to the light, and then the image can be generated on the screen. When the image on the screen is like an advertising light box, the light from the lamp tube in the light box enters the human eye through the patterned film.

Due to the extremely low light transmittance of liquid crystals, the brightness of the LCD TV should be made to achieve a perfect display screen. The brightness of the backlight is very high, so the life of the backlight is the life of the LCD TV. Generally, the life of the backlight of the LCD TV is basically above 50,000 hours. In other words, if you use an LCD TV for an average of 5 hours a day, the life span of 50,000 hours is equivalent to 27 years of using the LCD TV.

Backlight adjustment
Automatic backlight adjustment refers to the function that the vehicle-mounted display device can automatically sense the light intensity of the different environments in which the car is located, thereby automatically adjusting the brightness and Contrast of the screen to suit the human eye. That is to say, the brightness and contrast will be lowered in a dark environment, and the brightness and contrast will be increased in a brighter environment. For a car, the luminous intensity of the surrounding environment changes all the time during driving. When the outside light is dark, an over-bright screen will make people feel very dazzling, and when the outside light is brighter, it will be unsightly. The picture is clearly displayed, and automatic backlight adjustment can solve these problems, can improve the comfort of human eyes, and can also protect eyesight.