Recently, in the Baidu Index, the search term "the difference between LCD and LED" still ranks in the top ten. In response to so many netizens' doubts about the distinction between the two, the editor has specially sorted out the relevant knowledge of LCD and LED. , For your reference and learning.
La différence entre l'affichage led et l'affichage lcd
affichage LED
One, the definition of distinction
LCD (short for Liquid Crystal Display) liquid crystal display. The structure of LCD is to place a liquid crystal cell between two parallel glass substrates. TFT (thin film transistor) is set on the lower substrate glass, and a color filter is set on the upper substrate glass. The liquid crystal molecules are controlled by the signal and voltage changes on the TFT. Rotate the direction, so as to achieve the display purpose by controlling whether the polarized light of each pixel point is emitted or not.
LED is the abbreviation of LightEmittingDiode. LED applications can be divided into two categories: one is LED display; the other is LED single tube application, including backlight LED, infrared LED and so on. As far as LED displays are concerned, China's design and production technology levels are basically in line with the international level. The LED display is composed of an array of light-emitting diodes. It adopts low-voltage scanning drive, and has the characteristics of low power consumption, long service life, low cost, high brightness, low failure, large viewing angle, and long visual distance.
Écran d'épissage LCD
affichage LCD
Second, the principle of backlight distinction
In the current market, liquid crystal displays are mainly divided into two categories, one is a liquid crystal display using traditional CCFL (cold cathode fluorescent lamp), and the other is a liquid crystal display using LED (light emitting diode) backlight. Many consumers directly refer to the first type of display as LCD, and the second type of display as LED. In fact, this statement is incorrect. Therefore, when distinguishing between LCD and LED, it can also be distinguished from its backlight principle.
LED backlight principle
The LED backlight uses light-emitting diodes as the backlight source. 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.
LED light-emitting technology has significant color advantages, so it is favored in display manufacturing. The outdated CCFL (Cold Cathode Backlight) technology is limited due to its own frequency spectrum, and the color gamut range is greatly restricted. The better performance is only about 70 percent of the NTSC color gamut. Higher color gamut effects require a higher cost. cost.
However, the use of LED as a backlight source is completely different, because the light of LED (light emitting diode) covers a wider chromatogram range, and the light-emitting area is more uniform. The normal color gamut range can easily reach 100 percent to 130 percent , which is not like traditional CCFL backlights. The same 30 percent color loss occurs. Therefore, the color of the LED backlight display is fuller, the details of the picture are clearer, and the color transition is more natural.
CCFL backlight principle
The physical structure of the CCFL (cold cathode fluorescent lamp) backlight is to enclose an inert gas Ne plus Ar mixed gas in a glass tube, which contains a trace amount of mercury vapor (a few mg), and coat the inner wall of the glass with phosphor. The working principle is that when a high voltage is applied to both ends of the tube, a small number of electrons in the tube impact 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, it excites and emits 253.7nm ultraviolet Light, the generated ultraviolet light excites the phosphor coated on the inner wall of the tube to generate visible light. The life of a CCFL lamp is generally defined as: at an ambient temperature of 25 degree , the lamp is driven with a rated current, and the length of working time when the brightness is reduced to 50 percent of the initial brightness is the lamp life. At present, the nominal life of LCD TV backlights 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.
At present, a large part of the displays still use traditional CCFL backlights, but the price advantage of LED backlight displays is getting smaller and smaller. The price of LED backlight displays under 18 inches is almost the same as that of CCFL displays. It is expected that in the second half of this year, the 23-inch price will be the same as the corresponding size of the CCFL backlit display.
Three, distinguish the advantages and disadvantages:
Introduction to the advantages and disadvantages of LED backlight light source
advantage:
1. The screen can be made thinner. We pay attention to some liquid crystal displays. You can see several CCFL tubes arranged in filaments. In order to make the screen emit light evenly, some other devices need to be added. Thin; while the backlight is different, the LED backlight itself is a flat luminescent material, no need to add other devices.
2. No yellowing or dimming. CCFL fluorescent lamps, like fluorescent lamps, will age after a long period of time. Therefore, traditional notebook screens will turn yellow and dim after two or three years, while the lifespan of LED backlight screens will be much longer, at least two. three times.
3. More energy-saving LED is a kind of semiconductor, works under low voltage, simple structure, low power consumption.
4. More environmentally friendly The mercury in CCFL lights has a lot of pollution to the environment, and it is difficult to recycle harmlessly.
shortcoming:
1. The relative price is relatively high. At present, the price difference between the traditional CCFL backlight display and the traditional CCFL backlight display is between 100-300 yuan under the same specifications.
Introduction to the advantages and disadvantages of CCFL backlight
advantage:
1. Long time to market, relatively mature technology
2. The color is more stable, and professional monitors are still used
3. The price is relatively low
shortcoming:
1. The service life is short. The service life of CCFL backlight is generally 15,000 hours to 25,000 hours. After 2 to 3 years of use, the LCD screen will darken and turn yellow, which is caused by the short service life of CCFL.
2. Complex structure and poor brightness output uniformity. When displaying an all-white or all-black picture, the difference in brightness between the edges of the screen and the center of the screen is very obvious.
3. Larger volume
4. High power consumption and high heat generation
Simply put, LCD and LED are two different display technologies. LCD is a display screen composed of liquid crystals, while LED is a display screen composed of light-emitting diodes. However, the LED display currently on the market is not a true LED display. To be precise, it is an LED-backlit liquid crystal display. The liquid crystal panel is still a traditional LCD display. To understand the difference between the two in more detail, we must start with the principles of CCFL and LED.
