Comparison between LED backlight technology and traditional CCFL backlight technology

LED backlight greatly improves the color of LCD monitors.
Why has QUALIA005 attracted widespread attention? The most important reason is that the colors of QUALIA LCD color TVs are particularly bright. In the video field, people generally use NTSC as a standard to measure the color reproduction characteristics of video equipment. This indicator refers to the saturation of various colors that the display device can display in the entire color space, that is, the degree to which blue, green, and red can be displayed. For traditional LCD TVs and monitors, the color gamut that can be covered is only 65% ​​to 75% of the NTSC standard. If we look closely at its color gamut curve, we will find that the green, yellow, and red parts are far from the standard. Therefore, the color range of traditional LCD TVs is small, and it is difficult to perfectly present natural scenes such as green grass and the sea.

As we know, LCDs do not emit light by themselves. They rely on backlight sources to transmit light through the display panel to display graphics and images. Therefore, the backlight technology directly affects the picture quality of LCD TVs. Traditional LCDs usually use cold cathode fluorescent lamps (CCFL) as light sources, and it is CCFL that causes the color of LCDs to be not rich enough and the color reproduction is poor. Let's look at Sony QUALIA005 series TVs, which expand the color gamut of LCD TVs to 105% of the NTSC standard, and can basically reproduce all the natural scenes we observe. The core is to use LED backlight sources instead of traditional CCFL backlight sources.

LED backlight technology leading advantages
As the backlight source of LCD, LED has many unique advantages in addition to the color gamut compared with traditional backlight technology, which can be summarized into ten aspects:

1) LED backlight has a better color gamut. Its color expression is stronger than CCFL backlight, which can make up for the insufficient number of display colors of LCD technology and has good color reproduction;

2) The service life of LED can be up to 100,000 hours. Even if it is used continuously for 10 hours a day, it can be used continuously for 27 years, which greatly extends the service life of LCD TV and can obtain an overwhelming advantage over plasma technology;

3) Large brightness adjustment range. It is easy to achieve LED power control, unlike CCFL, which has a threshold for the minimum brightness. Therefore, whether in bright outdoors or in a dark room, users can easily adjust the brightness of the display device to the most pleasing state;

4) Perfect motion images. The flickering frequency of traditional CCFL lamps is low, and the dynamic scene may cause the picture to jump. LED backlight can flexibly adjust the light frequency, and the frequency is much higher than CCFL, so it can perfectly present motion pictures;

5) Real-time color management. Since the red, green and blue colors emit light independently, it is easy to accurately control the current display color characteristics;

6) The backlight white balance can be adjusted while ensuring the overall contrast. When the user's video source switches between the computer and the DVD player, the white balance can be easily adjusted between 9600K and 6500K without sacrificing brightness and contrast;

7) It can provide a continuous array light source for large-size screens. LED is a planar light source. The most basic light-emitting unit is a square with a side length of 3 to 5mm. After packaging, it is very easy to combine together to form a surface light source of a given area. It has good brightness uniformity. If it is used as a backlight source for an LCD TV, the required auxiliary optical components can be made very simple, and the screen brightness uniformity is even better;

8) Safety. LED uses a low-voltage power supply of 5 to 24V, which is very safe, and the design of the power supply module is also quite simple;

9) Environmental protection. LED light sources do not generate any rays, nor do they contain toxic substances such as mercury. They can be said to be green and environmentally friendly light sources;

10) Shockproof. The planar structure gives LED a stable internal structure and excellent shock resistance.

Table 1. Comparison between LED and CCFL
CCFL LED
color gamut 72% 105%
Color temperature fixed variable
Stroboscopic drive required or not
Rise/fall time 500 milliseconds 20 nanoseconds
Lifespan 50,000 hours 100,000 hours
Power consumption 110 watts 415 watts
Thickness 32.5 mm 45 mm
Number of lamps/LEDs 16 455

Today, when LCDs have become mainstream displays, LED backlight sources are gradually showing strong application prospects with their unique and overwhelming advantages.

Current problems with LED backlights
LED backlight technology, like many new technologies, has many attractive advantages, but if LED wants to occupy the mainstream of large-size LCD backlights, it still needs to solve some technical difficulties. Through the comparison in Table 1, we have found that LED is at a disadvantage in terms of power consumption. In addition, there are problems such as high cost and poor consistency.

1) The luminous efficiency of LED is low, and it consumes more power than the CCFL backlight of the same size. At present, the output luminous flux of CCFL is mostly in the range of 5000-7000lm, and the output luminous flux of the actual screen is higher than 300lm, while most LED backlights cannot reach this indicator. However, there are now a large number of companies around the world engaged in related research, and the luminous efficiency of LED has increased quite rapidly. At present, high-brightness LED backlights with a luminous flux of 10,000lm have also appeared, and I believe that they are only a stone's throw away from maturity.

2) The cost is too high and the price is expensive. For the backlight of the same size, the price of LED is 4 times that of CCFL. For the current market with fierce price competition, manufacturers are somewhat discouraged. Only Sony does not care about the cost for image quality. Of course, as the technology matures and the scale of production increases, the cost of LED backlight will gradually decrease.

3) There is a problem with the consistency of white light when using LED as a backlight source, which is a disadvantage compared to CCFL.

4) LED is more difficult to design than linear light source CCFL in terms of dot design, and the radial light intensity attenuation of LED needs to be considered.

5) RGB LED backlight sources will produce color shift over time, and the wavelength will change with temperature, producing different colors.