In comparison, what are the differences between the backlight principles of LCD and LED?

When it comes to display technology, the first thing people think of is liquid crystal display (LCD). As time goes by, some new display technologies begin to enter people's lives, and LED display technology is one of them. Without a more systematic understanding of the differences between the two display technologies, it is difficult to find the differences. This article will explain the difference between LCD and LED from the fundamentals of the display, the principle of backlight.

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 The energy is released in the form of light radiation. Light-emitting diodes with different light-emitting properties can be obtained by using different semiconductor materials.

LED lighting technology has significant color advantages, so it is favored in display manufacturing. The currently outdated CCFL (cold cathode backlight) technology has a greatly limited color gamut due to its own spectrum limitations. The best performance is only about 70% of the NTSC color gamut. Higher color gamut effects require higher costs. cost.

But using LED as the backlight source is completely different, because the light of LED (light-emitting diode) covers a wider range of color spectrum, the light-emitting area is more uniform, and the normal color gamut range can easily reach 100% to 130%, unlike traditional CCFL backlight There is also a 30% color loss. Therefore, LED backlight displays have fuller colors, clearer picture details, and more natural color transitions.

CCFL backlight principle

The physical composition of a CCFL (cold cathode fluorescent lamp) backlight is a glass tube filled with an inert gas Ne+Ar mixture containing a trace amount of mercury vapor (several mg), and a phosphor 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 collide with the electrodes at high speed to produce secondary electron emission and start discharge. After the mercury or inert gas in the tube is impacted by the electrons, it is excited to radiate ultraviolet light of 253.7nm. The ultraviolet light generated excites the phosphor coated on the inner wall of the tube to produce visible light. The life of a CCFL lamp is generally defined as: when the lamp is driven at a rated current at an ambient temperature of 25°C, the length of time during which 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. CCFL (cold cathode fluorescent lamp) backlight is characterized by low cost, but the color performance is not as good as LED backlight.

Currently, a large proportion of displays still use traditional CCFL backlights, but the price advantage over LED-backlit displays has become smaller and smaller. The price of LED-backlit displays below 18 inches is almost the same as that of CCFL displays. It is expected that in the second half of this year, the price of 23-inch displays will be the same as that of CCFL backlit displays of corresponding sizes.

In addition, everyone needs to pay attention to the fact that the popular displays on the market now mainly use two technologies, one is cold cathode fluorescent tubes, and the other is LED backlight technology. However, many people confuse LCD display with cold cathode fluorescent tubes, which is obviously incorrect. They should be distinguished from the perspective of backlight principle, which is the most correct way of understanding. I hope everyone can gain something after reading this article.