LCD panel to LED lighting conversion

Even if you buy a LCD and previously purchased LCD seems to have the same characteristics, may in fact have changed in the back. For the size of 15 inches below the display, the time tested LCD cold cathode tube (CCFL) lighting system is rapidly being replaced by light-emitting diodes.

This is similar to the transistor to replace the vacuum tube changes, there are many reasons, but also a lot of derivative products. The change is based on the recent increase in brightness of white LED, so that it can be used for sizes larger than 4 to 6 inches of PDA display LCD backlight or side light. In addition, the price is also an important factor.

"CCFL is going to be history," says Richard McKay, general manager of Apollo's Display display unit, and many other industry sources agree with the idea that Systems.

"LED will quickly replace the 10 inch LCD backlight and larger display," vice president of business development LED driver Lynk Labs Stewart Hough technology company said, "almost all of the CCFL backlight suppliers now do LED backlight. "

Environmental factors

One of the main reasons for LED backlight and side light is the rise of the EU's RoHS directive, the EU Member States to eliminate the electronic device sold since July 1, 2006 contain any lead, cadmium and mercury, six chromium, polybrominated biphenyls and polybrominated diphenyl ether.

Mercury is the main component of CCFL and other types of fluorescent lighting. Although the supplier has lowered its mercury content in the fluorescent tube, and mercury free version is also under discussion, but the LCD has more advantages make CCFL destined to be eliminated in the manufacturing process.

According to the LCD side light professional manufacturer Global Lighting Technologies (GLT) sales director David DeAgazio said that the complete elimination of the use of mercury may bring a series of new problems CCFL.

"The global market is constantly pursuing environmental protection, and as far as possible to achieve energy conservation and zero pollution," McKay said, "LED lighting also came into being. "

Power issues

According to LCD manufacturer Kyocera Industrial Ceramics display Department Marketing Manager Joe Maurer, said the green effect is one of the two main reasons driving LCD to lighting changes.

Another driver is the voltage. Maurer will be a higher starting CCFL AC voltage requirements are limited to 1500 ~ 1600Vac, stable delay to 700 or 800Vac. Therefore, it is necessary to use a power converter, so as to be able to operate through the DC power supply, but this increases the cost of application, occupation area and weight.

By contrast, a typical LED lighting subsystem can operate at 12 to 24Vdc or lower voltage, Maurer said, you can remove the converter and remove EMI. "

Kyocera LCD Application Engineer Bob Joslyn said that the use of low-voltage LED technology, but also makes it easier to achieve brightness control.

Efficiency and service life

From mid 1980s, LCD backlight, cold cathode tube after decades later in efficiency and service life has made great progress, but the traditional technology of the old in the major future development prospects remain bleak. In contrast, LED alternative technology is progressing rapidly, and even out of 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, CCFL rated service life (Ban Liang) between 8000 ~ 100000 hours. Some power will bring the advantages of efficiency on the CCFL, and some will bring efficiency advantages for LED.

But at this stage, LED and CCFL seem to be very close to all the relevant parameters, such as luminous efficiency (range of 50 ~ 100 lumens /W) and service life (from 25000 to 24 hours).

But there are also some subtle differences. For example, due to the higher efficiency of LED, it is naturally more suitable for side light applications than CCFL. "CCFL's luminous efficiency may be higher than that of LED," DeAgazio said. "But CCFL is a light source, so it may waste a lot of light. In contrast, LED has high directivity, so it is easy to effectively combine with the light guide. "

As for the lifetime, the LED and CCFL half light time depends largely on the difficulty of component drive. In this way, LED has a higher complexity: moderate thermal management is a key factor in determining the duration of components.

Source: Electronic Engineering album