What is the difference between LCD and LED display principle?
- Apr 25, 2018 -

                 

When it comes to display technology, people first think of liquid crystal display (LCD). With the passage of time, some new display technologies have begun to enter people's lives. LED display technology is one of them. If there is no systematic understanding of the differences between the two display technologies, it is difficult to find the difference. This article will explain the difference between LCD and LED from the fundamental of the display and the principle of backlight.


                                 

 

LED backlight principle

The LED backlight uses a light emitting diode as a backlight source. Light-emitting diodes are made of several thin layers of doped semiconductor materials, one layer with an excessive amount of electrons, and the other lacking electrons to form positively charged holes. Current passes through during operation, and 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 having different light emitting characteristics can be obtained.

LED lighting technology has obvious advantages in color, so it is favored in display manufacturing. Currently outdated CCFL (Cold Cathode Backlight) technology has a limited range of color gamut due to its own frequency spectrum limitation. The best performance is only about 70% of the NTSC color gamut, and the higher color gamut effect will have to pay a higher price. cost.

However, the use of LED as a backlight is completely different, because the LED (Light Emitting Diode) covers a wider spectrum of light, the light emitting area is more uniform, and the normal color gamut can easily reach 100% to 130%, unlike traditional CCFL backlighting. The same 30% color loss occurs. Therefore, the color of the LED-backlit display is more full, the detail of the picture is clearer, and the color transition is more natural.


CCFL backlight principle

The physical structure of the CCFL (cold cathode fluorescent lamp) backlight is a Nebula gas Ne+Ar mixed gas, which contains a trace amount of mercury vapor (a few mg), and a fluorescent body is coated on the inner wall of the glass. The working principle is that when high voltage is applied to both ends of the lamp, a small number of electrons in the lamp will impact the electrode at high speed to generate secondary electron emission and begin to discharge. After the mercury or inert gas in the tube is impacted by electrons, the radiation excites the UV at 253.7 nm. In the light, the generated ultraviolet light excites the phosphor coated on the inner wall of the tube to generate visible light. CCFL lamp life is generally defined as: In the ambient temperature of 25 °C, with the rated current to drive the lamp, the brightness is reduced to the initial brightness of 50% of the working time length of the lamp life. At present, the nominal life of LCD TV backlight can reach 60000 hours. The CCFL (Cold Cathode Fluorescent Lamp) backlight is characterized by low cost, but the color performance is inferior to the LED backlight.

There is still a large part of the display using the traditional CCFL backlight, but the current price advantage compared to LED-backlit displays has become smaller and smaller, and the price of LED-backlit displays below 18 inches is almost the same as that of CCFL monitors. It is expected that in the second half of the year, the 23-inch price will also be the same as the corresponding size CCFL backlight display.


                     

In addition, it should be noted that the popular monitors on the market today mainly use two technologies, one is a cold cathode fluorescent lamp and the other is an LED backlight technology. However, many people confuse LCD with cold cathode fluorescent tubes. This is obviously not correct. It should be distinguished from the perspective of backlight principle. This is the most correct way to understand. I hope everyone can read the article after the harvest.