LED backlight technology achievements imperial road

With the return of LED-backlit LCD monitors in 2009, the purchase of displays has become simpler. LED backlight LCDs have adopted more advanced white LED devices to reduce costs, and many fashion concepts such as environmental protection, energy saving, and lightweight have been won. The favor of mainstream consumers, then what exactly LED backlight display technology? What advantages does it have compared to traditional CCFL backlighting?

The LED technology was born very early. In 1923, Lossen.ow studied light emission in the impurity-doped PN junction of the semiconductor SIC, and studied the Light Emitting Diode (LED). The technology did not receive sufficient attention at that time. Until 1962, the joint labs of GE, Monsanto and IBM developed a red-emitting gallium arsenide phosphide (GaAsP) semiconductor compound. Since then, visible light emitting diodes have entered the commercial development process. . With the advancement of technology, different colors of light-emitting LED devices have come out one after another. In the 1970s, due to the large number of applications of LED devices in homes and office equipment, the price of LEDs has plummeted.

LED has been widely used in many aspects due to its inherent characteristics, such as power saving, long life, shock resistance, fast response speed, cold light source, etc. In the stadium, the large-screen display system can match live and match scores, Time, wonderful playback, etc.; in the transportation industry, road operations can be displayed; in the financial industry, financial information, such as stocks, exchange rates, interest rates, etc., can be displayed in real time; large-screen advertisements in many shopping malls are also a new vision brought by LED technology. Feelings.

The DIY industry has achieved unprecedented development in the early 21st century. Displays as an important display device have also evolved from CRTs and LCDs to hot, LED-backlit displays. Today we discuss LED display technology together.

LED device light-emitting principle After a brief history of LED development, we first need to understand the LED light-emitting principle, light-emitting diodes mainly composed of PN junction chip, electrodes and optical systems. Its luminous body - the area of ​​the chip is 10.12mil (1mil = 0.0254 square millimeters), the current international large-chip LED, chip area of ​​40mil.

The luminescence process includes three parts: carrier injection under forward bias, composite radiation, and light energy transmission. The tiny semiconductor wafer is encapsulated in a clean epoxy resin. When the electrons pass through the wafer, the negatively charged electrons move to the positively charged hole region and recombine with it, and electrons and holes disappear while generating photons. The greater the energy (band gap) between electrons and holes, the higher the energy of the photons generated. The energy of photons in turn corresponds to the color of light. Within the spectrum of visible light, blue light and purple light carry the most energy, and orange light and red light carry the least energy. Because different materials have different band gaps, different colors of light can be emitted.

The basic characteristics of LED light source High luminous efficiency LED After several decades of technical improvements, its luminous efficiency has been greatly improved. Incandescent lamps and tungsten halogen lamps have a luminous efficiency of 12-24 lm/W, fluorescent lamps 50-70 lm/W, and sodium lamps 90-140 lm/W, and most of the power consumption becomes heat loss. LED light efficiency will be improved to reach 50 ~ 200 lumens / watt, and its light monochromaticity is good, narrow spectrum, without filtering can emit colored visible light directly.

Low power consumption LED single-tube power 0.03 ~ 0.06 watts, using DC drive, single-tube drive voltage 1.5 ~ 3.5 volts, current 15 ~ 18 mA, the reaction speed, can operate at high frequency.

The long service life adopts the electron light field to radiate and radiate, and the filament has the disadvantages of easy to burn, heat deposition, and light attenuation. Compared with the life of 50,000 hours of CCFL light source, LED originals generally reach a lifetime of about 100,000 hours, and during the production process, CCFL does not want to use mercury that will pollute the environment, and it is also more environmentally friendly.

Safety, reliability, low heat, no heat radiation, cold light source, can be safe to touch: can accurately control the light and light angle, soft light color, no glare; does not contain mercury, sodium and other substances that may harm health. The built-in micro-processing system can control the luminous intensity, adjust the luminous mode, and realize the combination of light and art.

The purity of the light emitted by high color purity LED devices is very high, and the performance in the spectrum is that the light is concentrated on a small wavelength.

The high response time compared to the millisecond response time of the CCFL light source enables the LED light source to achieve a nanosecond response time. Therefore, it also has considerable significance for improving the smearing effect of the liquid crystal display.

The defects of the traditional CCFL backlight Before we reveal the defects of the CCFL backlight, let us review the imaging principle of the LCD.

It is the use of organic crystal molecules that are liquid at room temperature, subject to change in the voltage arrangement order, so that the white light emitted by the backlight is transmitted by liquid crystal molecules in different states, and then filtered by three colors of RGB colors. Imaging is achieved after the membrane. If we are close to the screen of the LCD, we will find that the LCD consists of tiny red, green and blue dots. By analogy, the imaging principle of LCD is like putting a light behind a window. By controlling the switch of the window, you can control the light.

After understanding the imaging principle of LCDs and the characteristics of LED products, we look back at the performance of today's traditional LCD displays. Since its birth, LCD monitors have not been able to solve their congenital defects, such as motion tailing, poor contrast, and small color gamut. These are all derived from CCFL type backlights.

What is CCFL?

Cold Cathode Fluorescent Lamps (CCFL) cold cathode tubes. Whether it is from the light-emitting principle or the physical structure, the CCFL light source and the fluorescent tube that we use everyday are very close. Through the electrodes at both ends of the lamp tube, ultraviolet rays excited by gaseous mercury in the lamp tube collide with the phosphor on the tube wall, thereby emitting light.

Even if CCFL light source defects are used in mainstream displays, LCD TVs, etc., it is not an optimal solution. Subject to the technical principle and production process of CCFL, CCFLs are generally tubular light sources. To achieve a uniform backlight effect, a large number of lamps are used to simulate a true surface light source. The resulting high power consumption and high heat are very obvious, and they cannot achieve a perfect planar light source.

CCFL light source defect The lifetime of the two CCFL light sources is only about 50,000 hours, and as the use time increases, the light from the light source will become dull and yellow. Since the backlight source of the LCD TV maintains a constant state as long as it is turned on, the LCD TV will suffer from significant color cast and brightness degradation problems after a few years of use.

CCFL light source defects The brightness of three CCFLs is generally constant. Even if the liquid crystal molecules are fully closed, some light will be transmitted through them. Therefore, current LCD TVs are difficult to exhibit true black color. Caused the LCD TV's poor contrast.

CCFL Light Source Defects The biggest drawback of the four CCFLs comes from spectral deficiencies. As we mentioned above, the white light emitted by the backlight must pass through the RGB color filter before it can be imaged. Therefore, the wavelength of the R/G/B primary light in the white light emitted by the backlight (ie, the purity of the three primary colors). Will directly affect the final color effect of the monitor. From this perspective, the white light emitted by the CCFL is not a very ideal light source with spectral characteristics. Therefore, most LCD displays on the market can only reach 60%-78% of the standard NTSC color gamut standard, and the color effect is naturally greatly reduced.

New LED display technology analysis The LED light sources used in various liquid crystal display devices provide a large area of ​​uniform backlight by a large number of LED units arranged in a plane. According to the different LED light colors, it can be divided into white LED backlight source and RGB-LED backlight source. The advantages of white LED technology are mainly reflected in the power consumption. Therefore, it is widely used in mobile devices that require high power consumption. Since 2004, many notebook computers have begun to adopt this technology.

LED color gamut advantage RGB-LED backlight source, through the LED device that can emit high purity red, green, blue light, to achieve the wide color gamut range that can not be achieved by the traditional CCFL light source. At present, mainstream RGB-LED backlight sources can already reach 105% NTSC color gamut, and as long as more powerful LED devices are used, more than 120% NTSC color gamut can already be achieved. This will be a very effective means of improving the quality of the display, which is mainly based on restored images.

In addition to good color gamut performance, the use of RGB-LED light source can also effectively enhance the contrast of the display, and achieve a more precise picture of the color gradation and layering. Since the entire backlight is made up of many tiny LED light emitting units, accurate luminance control can be achieved for each of the light emitting devices. According to the characteristics of the original picture, it is possible to perform the correction of the brightness in a small area. For example, in a bright contrast picture, the LED backlight in the dark area can be completely turned off, and the LED backlight in the bright area achieves high-brightness output. The contrast enhancement effect will be unmatched by LCD monitors using CCFL light sources.

In addition to the enhancement of the picture quality, LCD monitors use RGB-LED light sources to achieve thinner thicknesses and smaller weights, and more in line with the concept of "flat" and modern aesthetics. The thickness of the V series products recently released by BenQ has been controlled to 15mm, and there is a possibility that it will be lighter and thinner in the future.

Current LED Insufficient Although RGB-LED technology has many advantages, it still has some inevitable limitations at the current level of technology. First of all, a large number of independent LED devices are used in LED backlights. Therefore, it is a relatively difficult problem to ensure the consistency of light emission of each device, which also leads to excessive scrap rate and cost burden. Secondly, although the color purity of RGB-LEDs is high, the attenuation of each LED color is not consistent after long-term use, which will also have a greater impact on picture quality.

Display the revolution is imperative At present, we have come into contact with the market of LED-backlit displays are using a lower cost white LED backlight display, RGB-LED technology due to its current cost of application and a small number of high-end products, environmental protection and energy-saving products Under the prevailing trend, more light-weight and energy-saving LED-backlit displays will undoubtedly replace CCFL-backlit displays.

Just as LCDs have hit the CRT in the past few years, the CCFL’s shame on the LED device’s lifetime of 100,000 hours and its strong color reproduction capabilities. The nano-response time also provides an excellent choice for users' games and entertainment. LED backlight displays will replace CCFLs by virtue of their demand for DC consumer trends such as being lighter, thinner, energy-saving and environmentally friendly.