LCD backlight technology changes from CCFL to LED

Even two LCD before and after you buy with properties quite consistent, but the screen behind may have changed. In a panel with a panel size of 15 inches or less, a time tested LCD cold cathode fluorescent lamp (CCFL) backlight system is rapidly being replaced by a light emitting diode (LED).

This shift is similar to the fact that transistors replace vacuum tubes for a number of reasons. The change is based on the recent increase in the brightness of white LED, so that the white LED can be achieved on the size of more than 4 to 6 inches PDA display LCD backlight or side lighting (edgELighting). Of course, the decline in prices is also a factor in this shift.

"CCFL will eventually become history," says Richard McKay, executive director of Display (VAR) Apollo, a display area, and many industry insiders agree with the idea.

"LED will quickly replace the LCD backlight display size of 10 inches and above the" professional to provide the driving technology for LED Lynk Labs, vice president of business development Stewart Hough said, "almost all of the CCFL backlight suppliers now have LED backlight. "

Green environmental factors

An important factor in the rise of LED backlight and the end face of the European Union is the implementation of the RoHS directive. The Directive provides for the elimination of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls and polybrominated diphenyl ethers (PBDEs) in electronic devices sold in EU Member States since July 1, 2006. Mercury is the main component of CCFL and other types of fluorescent lighting. Although the supplier has reduced the mercury content in its fluorescent tubes, and mercury free models are under discussion, but the additional advantages of LED CCFL is destined to be eliminated in the manufacturing process. Specializing in LCD face light technology Global Lighting Technologies sales director David DeAgazio pointed out that the elimination of Mercury will bring a series of new problems CCFL.

Not only that, the global market is increasingly green, need to achieve as much as possible to achieve energy saving and pollution-free, McKay said, and LED backlight can adapt to this trend. "

Lower power required for LED backlight

LCD manufacturers Kyocera Industrial Ceramics display Marketing Manager Joe Maurer said that the green effect is one of the two most important factors driving the LCD backlight backlight turned from CCFL to LED.

Another important factor is the voltage. Maurer said, CCFL AC voltage requirements are relatively high, start up to 1500 ~ 1600 Vac, and then stabilized to 700 or 800Vac. They also require a power inverter to work through a DC power supply, which increases the cost of the application, the occupied area and the weight. In contrast, a typical LED backlight subsystem works at "12 to 24Vdc or lower voltage," Maurer said. "You can remove the inverter and eliminate electromagnetic interference (EMI). "

In addition, Kyocera's LCD Application Engineer Bob Joslyn pointed out that the use of low voltage LED technology brightness control is easier to achieve.

Comparison of efficiency and service life

Since the mid 80s of last century, CCFL is a de (de facto) LCD backlight technology. After years of development, CCFL has made great progress in efficiency and service life, but in the future will continue to get great technological progress is very bleak prospects. In contrast, alternative LED technologies are developing rapidly, and this technology has a clear path to future development.

The comparison between CCFL and LED in brightness, efficiency, service life and so on is different from the supplier. For example, different CCFL rated service life (Ban Liang) between 8000 ~ 100000 hours, the difference is very large. Some sources refer to the highest efficiency of CCFL, and the other sources believe that LED is the most efficient.

Figure 1: Kyocera 5.7 inch VGA LCD, for example, LED face light energy at CCFL 60% power supply CCFL brightness of 80%

But in terms of efficiency, LED and CCFL seem to be close to all the relevant parameters, such as luminous efficiency (range of 50 ~ 100 lumens / watt), etc.. But there are some subtle differences. For example, the application of the end face should be, LED is more suitable than CCFL, the former is more efficient. "CCFL's luminous efficiency may be higher than that of LED," DeAgazio said. "But CCFL is a light source, so you can waste a lot of light. "In contrast, LED has a high degree of orientation, so it is easy to effectively combine with the light guide plate. "

As for the service life, the half bright time of LED and CCFL depends greatly on the drive mode of the device. LED has a higher degree of complexity, because proper thermal management is a key factor in determining device duration.

Color comparison

Compared with the glass shell CCFL, the advantages of LED include its excellent durability and better color. CCFL provides a wide spectrum of white light with LED based on the integration of the yellow phosphor layer of the blue light-emitting diodes to show the same level of light. But based on narrowband color red green blue (RGB), the RGB color filter white LED and LED LCD, and can produce the most saturated colors with the highest efficiency.

Both the CCFL and the LED chips can be backlit (either behind the display) or at the end of the light (on both sides, top, and bottom), and can be used to increase brightness. LED is usually presented as a string on a flexible substrate. Such devices are increasingly used in high-end HD TV (HDTV),