Analysis of LED application in backlight module

1. LEDs used in backlight modules have the advantage of saving power

LED is used as a light source in the backlight module to replace the traditional cold cathode fluorescent lamp (CCFL). It is not only light and thin, power-saving, small in size, long in life, low in voltage, and fast in startup, but also environmentally friendly. For laptops, depending on the processor and size, the power consumption of the LCD panel accounts for about one-third of the entire machine. Due to the low power consumption of LED, the current use time of NBs using LED backlight can be extended by more than 1.5 hours; and the thickness of the light guide plate with LED can be reduced from 2mm to 0.6mm (13.3-inch products), the thickness of the screen can be reduced, and the weight of the entire machine will also be reduced; and each CCFL currently contains about 2mg of mercury, using LED as a light source can reduce the use of mercury. If RGB three colors are used to mix white light, it can provide better color saturation, and the color of the TV screen will be brighter. LED can achieve regional dynamic control, and turn off when the screen is black in some areas to improve the light and dark contrast, while saving power. LED has a fast response speed. Using RGB three-color LED with fast-response liquid crystal, the color sequential method can be used to omit the use of color filters.

The luminous efficiency of LED is only 20-40lm/W, which is not as good as CCFL's 80lm/W. At the same time, the high cost is the biggest weakness of LED backlight modules. The unit price of a CCFL and a high-brightness LED is around US$1.5, but the number of LEDs used far exceeds that of CCFLs. In addition, LEDs have poor heat dissipation, and large-size TVs still need to add a heat dissipation substrate, which will be another expense. The color decay speed of each LED is different, and long-term use will cause color unevenness.

LCD upstream and downstream manufacturers have invested in LED factories. The main purpose is not to obtain LED production capacity but to consider technology. Technically, the packaging form of LED, the wavelength of light, the light angle, etc. will affect the backlight module. Panel factories and backlight module factories need to cooperate with LED manufacturers with close relationships to provide special specifications of products for various experiments and reliability tests. In addition, panel factories and backlight module factories have faced the problem of CCFL shortage. Mastering the source of materials has become an important issue for panel factories and backlight module factories. Investing in LED factories is to prevent the doubts of shortage after large-scale use of LEDs, rather than focusing on short-term benefits.

2. Impact and Observation Focus

Compared with CCFL, using LED as backlight source has advantages such as lightness, environmental protection, and power saving, but cost is the biggest disadvantage. It is estimated that the proportion of LED backlight used in notebook computers in 2007 will be less than 8%. The main reason is the competitive demand from other application fields. LEDs must be screened. How to get rid of LEDs that do not meet the requirements of backlight modules will be the most urgent issue to be solved. At the same time, TFT-LCD manufacturers and backlight modules want to lower prices to reduce costs, and LED manufacturers have good gross profit margins in other application fields. Whether they can supply in large quantities has also become a key issue.

In 2006, notebook computer manufacturers only launched 11.3-inch and 12.1-inch LED backlight notebook computers. Since there were not many notebook computers below 12.1 inches, and LED backlight was considered as a high-end model, the demand was limited. Starting from 2007, Apple, Asus, DELL and other computer manufacturers will successively launch 13.3-inch and even larger 15.4-inch products using LED as backlight, but they are still positioned as high-end models and have no intention of shipping in large quantities. If computer manufacturers do not change their product positioning of using LED backlight modules, it will not be of much help to the LED industry.

As for environmental protection, the European Union (EU) implemented the RoHS Directive (Restriction of Hazardous Substances in Electrical and Electronic Equipment) in July 2006 to ban the use of hazardous substances in electronic products. Although mercury is a regulated item, CCFLs can still be used due to an exclusion clause. Before the exclusion clause is abolished, the use of CCFLs cannot be forcibly excluded.

In the field of LCD TV, the cost of LED backlight module is too high, almost three times that of CCFL backlight module of the same size, and the price of LCD TV using LED backlight is more than 30% of the same size. CCFL manufacturers have also launched wide color gamut fluorescent tubes (Wide Colour Gamut-CCFL), which can reach more than 92% NTSC, but the current TV signal is only 82% NTSC, and the effect of high color saturation is still limited. Therefore, SONY and Samsung have launched LED backlight module LCD TVs, but the sales are not good. The significance of the technology indicator is more than the actual profit.

At present, LEDs are still mainly used in small and medium-sized devices below 10 inches. Laptops still need to wait for major computer manufacturers to launch mid-range products using LED backlight modules before the market can expand. As for televisions, there are still cost, technical and other issues to be resolved. In the next 2 to 3 years, high-end products and even technical strength demonstrations will probably still be the main focus.