LCD and LED: How to distinguish in three steps?

　　Recently, on the Baidu Index, the search term "difference between LCD and LED " still ranks among the top ten. In view of the doubts of so many netizens about the distinction between the two, the editor has specially compiled the relevant knowledge about LCD and LED for everyone's reference and study.

　　1. Definition and distinction

　　LCD (Liquid Crystal Display) is a liquid crystal display. The structure of LCD is to place a liquid crystal box between two parallel glass substrates, set TFT (thin film transistor) on the lower substrate glass, and set color filter on the upper substrate glass. The signal and voltage on the TFT are changed to control the rotation direction of the liquid crystal molecules, so as to control whether the polarized light of each pixel is emitted or not to achieve the display purpose.

　　LED is the abbreviation of Light Emitting Diode. LED applications can be divided into two categories: one is LED display screen; the other is LED single tube application, including backlight LED, infrared LED, etc. Now as far as LED display screen is concerned, China's design and production technology level is basically synchronized with the international level. LED display screen is composed 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, few failures, large viewing angle, and long viewing distance.

　　2. Backlight principle distinction

　　In the current market, LCD monitors are mainly divided into two categories, one is the LCD monitor using traditional CCFL (cold cathode fluorescent lamp), and the other is the LCD monitor using LED (light emitting diode) backlight. Many consumers directly call the first type of monitor LCD and the second type of monitor LED. In fact, this statement is incorrect. Therefore, when distinguishing LCD from LED, you can also distinguish them from their backlight principles.

　　LED backlight principle

　　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 working, current passes through, electrons and holes combine with each other, and excess energy is released in the form of light radiation. By using different semiconductor materials, light-emitting diodes with different luminous properties can be obtained.　　 The color advantage of LED luminous technology is significant, so it is highly favored in display manufacturing. The currently outdated CCFL (cold cathode backlight) technology is greatly limited in color gamut due to its own spectrum limitations. The best performance is only about 70% of the NTSC color gamut, and higher color gamut effects require higher costs.

　　But using LED as backlight is completely different, because LED (light-emitting diode) light covers a wider color spectrum, the luminous area is more uniform, and the normal color gamut can easily reach 100% to 130%, and there will be no 30% color loss like traditional CCFL backlight. Therefore, the color of LED backlight display is more saturated, the details of the picture are clearer, and the color transition is more natural.

　　CCFL backlight principle

　　The physical structure of CCFL (cold cathode fluorescent lamp) backlight source is to seal inert gas Ne+Ar mixed gas in a glass tube, which contains trace mercury vapor (several mg), and the inner wall of the glass is coated with phosphor. The working principle is that when high voltage is applied to both ends of the lamp tube, a small number of electrons in the lamp tube collide with the electrodes at high speed to produce secondary electron emission, and discharge begins. After the mercury or inert gas in the tube is hit by the electrons, it excites and radiates 253.7nm ultraviolet light. The generated ultraviolet light excites the phosphor coated on the inner wall of the tube to produce visible light. The life of CCFL lamp is generally defined as: at an ambient temperature of 25℃, the lamp tube is driven with rated current, and the working time length when the brightness is reduced to 50% of the initial brightness is the lamp life. At present, the nominal life of LCD TV backlight can reach 60,000 hours. The characteristics of CCFL (cold cathode fluorescent lamp) backlight source are low cost, but the color performance is not as good as LED backlight.

　　At present, a large number of monitors still use traditional CCFL backlights, but the price advantage over LED backlight monitors is getting smaller and smaller. The price of LED backlight monitors below 18 inches is almost the same as that of CCFL monitors. It is expected that in the second half of this year, the price of 23-inch monitors will also be on par with CCFL backlight monitors of the same size.

　　3. Advantages and disadvantages:

　　Introduction to the advantages and disadvantages of LED backlight sources

　　advantage:

　　1. The screen can be made thinner. If we look at some LCD monitors, we can see that there are several filamentary CCFL tubes arranged. In order to make the screen emit light evenly, some other devices need to be added, so it is impossible to make it very thin; but the backlight is different. The LED backlight source itself is a flat luminous material, and no other devices are needed. 2. It will not turn yellow or dark. CCFL fluorescent lamps, like fluorescent lamps, will age over time, so traditional laptop screens will turn yellow and dark after two or three years, while the life of LED backlight screens is much longer, at least two or three times longer.

　　3. More energy-saving LED is a semiconductor that works at low voltage, has a simple structure and low power consumption.

　　4. More environmentally friendly The mercury in CCFL lights is highly polluting to the environment and is difficult to recycle harmlessly.

　　shortcoming:

　　1. Relatively high price. Currently, the price difference between the display and traditional CCFL backlight display is between 100 and 300 yuan for the same specifications.

　　Introduction to the advantages and disadvantages of CCFL backlight

　　advantage:

　　1. Long time on the market, relatively mature technology

　　2. The color is more stable, and professional-grade monitors still use

　　3. The price is relatively low

　　shortcoming:

　　1. Short service life. The service life of CCFL backlight is generally 15,000 to 25,000 hours. After 2 to 3 years of use, the LCD screen will become dark and yellow, which is caused by the short service life of CCFL.

　　2. Complex structure and poor brightness output uniformity. When displaying a full white or full black picture, the difference in brightness between the edge and center of the screen is very obvious.

　　3. Large size

　　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 screens currently on the market are not true LED displays. To be precise, they are LED backlit liquid crystal displays, and the liquid crystal panel is still a traditional LCD display screen. To understand the difference between the two in more detail, we must start with the principles of CCFL and LED.