Distinguish the backlight principle of LCD and LED

- Oct 23, 2018-

Recently, on baidu index, the search term "difference between LCD and LED" still ranks in the top 10. In view of the doubts of so many netizens about the difference between the two, the editor specially organized the relevant knowledge of LCD and LED for everyone's reference and study.


Liquid Crystal Display (short for Liquid Crystal Display). The structure of the LCD is placed in the middle of the two pieces of parallel glass liquid crystal box, the substrate glass set on TFT (thin film transistor), set the color filter substrate glass on, on the TFT signal and the voltage change to control the rotation direction of the liquid crystal molecules, so as to achieve control of each pixel display emergent polarized light or not and to achieve.

An LED is an abbreviation for a Light Emitting Diode. LED applications can be divided into two categories: one is LED display; Second, single LED applications, including backlight LED, infrared LED, and so on. Now in terms of LED display, China's design and production technology is basically in sync with the international level. LED displays are made up of leds. It is driven by low voltage scanning and has the following features: less power consumption, long service life, low cost, high brightness, few failures, large visual Angle and long visual distance.

The backlight principle differentiates

In the current market, liquid crystal displays are mainly divided into two categories, one is the traditional CCFL(cold cathode fluorescent lamp tube) liquid crystal display, the other is the LED(light emitting diode) backlight liquid crystal display. Many consumers directly refer to the first type of display as LCD and the second type as LED. That's actually not true. Therefore, when differentiating LCD and LED, they can also be distinguished by their backlight principle.

Principle of LED backlight

LED backlight USES LED as backlight source. Light-emitting diodes are made of thin layers of doped semiconductor material, one with an excess of electrons, the other with a lack of electrons to form positively charged holes. The current passes through, the electrons and holes combine, and the excess energy is released in the form of light radiation. Different light-emitting diodes can be obtained by using different semiconductor materials.

LED technology has significant color advantages, so it is favored in display manufacturing. The current outdated CCFL(cold cathode backlight) technology, due to its own spectrum limitations, has a relatively limited range of color gamut. The best performance is only about 70% of the NTSC color gamut.

However, the use of LED as backlight is totally different, because the color spectrum covered by LED(light-emitting diode) is wider and the luminous area is more uniform, and the normal color range can easily reach 100% to 130%, without 30% color loss as traditional CCFL backlight. So the LED backlight display is fuller in color, the picture details are clearer and the color transition is more natural.

CCFL backlight principle

The physical composition of CCFL(cold cathode fluorescent lamp) backlight is sealed in a glass tube with inert gas Ne+Ar mixed gas, containing trace mercury vapour (mg), and coated with fluorescence in the glass inner wall. The working principle is that when the high voltage is added at both ends of the tube, a small number of electrons in the tube will collide with the electrode at high speed to generate secondary electron emission, and discharge begins. After the mercury or inert gas in the tube is impacted by the electron, the excitation radiation will be 253.7nm ultraviolet light, and the resulting ultraviolet light will be coated on the wall of the tube to generate visible light. CCFL lamp life is generally defined as: in the ambient temperature of 25 ℃, with rated current driving lamp, brightness to reduce 50% of the work to the original brightness time length of lamp life. At present, the nominal life of LCD TV backlight can reach 60,000 hours. CCFL(cold cathode fluorescent lamp) backlight is characterized by low cost, but the color performance is not as good as LED backlight.

A large proportion of displays still use traditional CCFL backlighting, but the price advantage of an LED backlight is now smaller and smaller, and the cost of an LED backlight under 18 inches is about the same as that of a CCFL display. The price of 23 inches is also expected to be on par with the CCFL back-lit displays of corresponding sizes in the second half of this year.