LED backlights greatly increase the color of LCD monitors
Why is QUALIA005 receiving widespread attention? The most important reason is that the color of QUALIA LCD TV is particularly bright. In the video field, NTSC is generally used as a measure of the color reproduction characteristics of video equipment. This indicator refers to the degree of saturation that the display device can display in various colors in the entire color space, that is, the extent to which blue, green, and red can be displayed. For traditional LCD TVs and displays, the range of gamuts that can be covered is only 65% ​​to 75% of the NTSC standard. If we look closely at the gamut curve, we find that the green, yellow, and red parts are farther away from the standard distance. Therefore, the color range of the conventional LCD TV is small, and it is difficult to perfectly present natural scenes such as green grass and sea.
We know that the LCD monitor itself does not emit light, it relies on the backlight to pass light through the display panel to display a graphic image. Therefore, the backlight technology directly affects the picture quality of the LCD TV. Conventional liquid crystal displays usually use cold cathode fluorescent lamps (CCFL) as a light source, and it is CCFL that causes the liquid crystal display to be not rich in color and poor in color reproduction. Let's look at the Sony QUALIA005 series of TVs, which extend the color gamut of LCD TVs to 105% of the NTSC standard, essentially recreating all of our observed natural scenes. At its core is the replacement of traditional CCFL backlights with LED backlights.
LED backlight technology leading edge
LED as the backlight of LCD, compared with the traditional backlight technology, in addition to the advantages of the color gamut range, there are many unique advantages, summarized into ten aspects:
1) LED backlights have a better color gamut. Its color expression is stronger than CCFL backlight, which can make a good complement to the liquid crystal technology with insufficient display color, and the color reproduction is good;
2) LEDs can last up to 100,000 hours. Even if it is used continuously for 10 hours every day, it can be used continuously for 27 years, which greatly prolongs the service life of LCD TVs, and has the advantage of overwhelming plasma technology;
3) The brightness adjustment range is large. It is easy to achieve LED power control, unlike the minimum brightness of CCFL. Therefore, it is easy for the user to adjust the brightness of the display device to the most pleasing state, whether in a bright outdoor or a black room.
4) Perfect motion picture. The flashing illuminating frequency of the conventional CCFL lamp is low, and the dynamic scene may cause the picture to jump. LED backlight can flexibly adjust the light-emitting frequency, and the frequency is much higher than CCFL, so it can perfectly display the moving picture;
5) Real-time color management. Since the red, green and blue colors are independent of each other, it is easy to accurately control the current display color characteristics;
6) The white balance of the backlight can be adjusted while ensuring the overall contrast. When the user's video source is switched between the computer and the DVD player, the white balance can be easily adjusted between 9600K and 6500K without sacrificing brightness and contrast;
7) A continuous array of light sources can be provided for large screen sizes. LED is a kind of planar light source. The most basic light-emitting unit is a square package with a length of 3 to 5 mm. It is easy to combine into a surface light source with a given area. It has good brightness uniformity, if it is used as a backlight for LCD TVs. Source, the required auxiliary optics can be made very simple, and the screen brightness uniformity is better;
8) Security. The LED uses a low voltage power supply of 5 to 24V, which is very safe, and the design of the power supply module is quite simple;
9) Environmental protection. LED light source does not produce any radiation, and there is no toxic substance such as mercury. It can be described as a green light source;
10) Earthquake resistance. The planar structure gives the LED a solid internal structure and excellent shock resistance.
| CCFL | led | |
| Color temperature | fixed | variable |
| Strobe drive | need | No need |
| Rise/fall time | 500 milliseconds | 20 nanoseconds |
| life | 50,000 hours | 100,000 hours |
| Power consumption | 110 watts | 415 watts |
| thickness | 32.5 mm | 45 mm |
| Number of lights / LEDs | 16 | 455 |
| Color gamut | 72% | 105% |
Nowadays, LCD backlights have become mainstream displays. With their unique and overwhelming advantages, LED backlights have gradually shown strong application prospects.
LED backlights now have problems
LED backlight technology has many attractive advantages like many new technologies, but LEDs need to solve some technical difficulties in order to occupy the mainstream of large-size LCD backlights. Through the comparison of Table 1, we have found that LEDs are at a disadvantage in terms of power consumption, in addition to the problems of high cost and poor consistency.
1) LEDs have low luminous efficiency and consume more power than equivalent CCFL backlights. At present, the output luminous flux of CCFL is mostly in the range of 5000 to 7000 lm, and the output luminous flux of the actual screen is higher than 300 lm, and most LED backlights cannot reach this index. However, there are a large number of companies in the world engaged in related research, LED luminous efficiency is increasing quite fast, the current luminous flux reaches 10000lm
The high-brightness LED backlight has also appeared, and it is believed that it is only a stone's throw away from maturity.
2) The cost is too high, the price is high, the backlight of the same size, the LED is 4 times the price of CCFL. For the current market where price competition is fierce, the manufacturers are somewhat discouraged. Only Sony does not cost for image quality. Of course, as the process matures and the scale of production increases, the cost of LED backlights will gradually decrease.
3) There is a problem of white light consistency with LED as a backlight, which is a disadvantage compared to CCFL.
4) LED is more difficult to design than the linear light source CCFL in the dot design, and it is necessary to consider the attenuation of the light intensity of the LED radiation.
5) RGB LED backlight time will cause the color shift wavelength to change with temperature, resulting in different colors.
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