White LED backlight LCD TV expected to be released ahead of schedule

Recently, LED backlight LCD TVs have become a hot topic, and various LCD TV manufacturers have started to engage in this business. In order to improve their brand image, Korean manufacturers have adopted a strategy of calling LCD TVs equipped with LED backlights "LEDTV". In order to distinguish them from display devices using LED units, they will be called "LEDLCDTV" below.

The LED LCD TV market is expected to grow significantly starting this year. In this market, South Korea's Samsung Electronics has taken the lead and become the leader. Sharp also seems to be planning to equip its new generation of TVs with LED backlights, which are sold at ultra-low power consumption.

The reasons for the hot LED LCD TV market are as follows:

First, the luminous efficiency of white LEDs has been increasing year by year, and the mass production effect has continuously reduced the unit price. At present, high color rendering LEDs have also achieved a luminous efficiency of about 100lm/W, and the industry generally recognizes that it will reach about 150lm/W around 2015. When LED backlight LCD panels first came out, they used RGB three-color LEDs, and the selling point was that the color performance range exceeded 100% of the NTSC ratio. However, the power consumption was about twice as high, and the price was also very high, so it could only be used in a very small number of high-end models. If white LEDs are used, although the color performance range will not be significantly larger than that of cold cathode tubes (CCFL), it is very competitive in terms of power consumption and cost.

Second, with the advancement of light guide plate technology, the illumination (EdgeLight) method, whether it is an edge type or a direct type, can obtain uniform diffuse light by utilizing the thin characteristics of LED. In this way, a module with a thickness thinner than before, power consumption equal to or lower than CCFL type when all lights are on, and basically the same cost can be realized. LED backlights can easily adjust the brightness of the display, so dynamic contrast adjustment technology widely used in portable terminals can also be used. Therefore, compared with the power consumption when all lights are on, the power consumption of standard images can be reduced. In other words, if it is an average image, the power consumption can be completely lower than that of CCFL type. If local dimming technology is used, it is expected to further reduce power consumption and improve contrast.

Possibility of using local dimming technology

The two-dimensional local dimming technology is used to achieve the maximum contrast while minimizing the power consumption of LCD TVs. This technology divides the screen into hundreds of blocks, adjusts the brightness of the direct-lit LED units corresponding to each block in real time, and corrects the signal to form the best contrast curve for each block.

This technology has no cost advantage due to the increase in circuit scale and the number of electronic components. In addition, there is a fatal problem. That is, the output brightness of all LED units from low brightness to high brightness must be compensated with absolute values. To solve this problem, inspection and adjustment before delivery takes a lot of time and is very costly. In addition, each LED unit will produce different degrees of brightness degradation, and may also cause aging or uneven brightness. Therefore, it is generally believed that the possibility of popularizing two-dimensional local dimming technology in mass-produced LCD TVs (VolumeZone) is very low.

If two-dimensional local dimming technology is not required, it is easier to adopt edge-lit LED backlights than direct-lit ones. From this point of view, Samsung's strategy of "fully adopting edge-lit white LED backlights" is very clear.

Samsung exhibited the power consumption of the edge-lit white LED backlight LCD modules for TV at the Korean Display Association and Exhibition "IMID2009/KES2009" as "32-inch Max55WTyp38W" and "40-inch Max76WTyp53W". The power consumption value when Typ (standard image display) is less than Max (full white display) is believed to be the result of dynamic contrast adjustment that can change the backlight brightness. If the power consumption of the digital tuner, image processing circuit, and audio circuit is about 20W, the power consumption of the 32-inch TV can be reduced to less than 60W when displaying a standard image, and the 40-inch model can be reduced to less than 75W. In the future, white LED LCD TV may become the flagship model of each manufacturer that promotes a low power consumption strategy.

At the display-related exhibition "IDW2009" held in December 2009, there was a technical report (paper number DES2-3) on local dimming of edge-lit white LED backlights. Since the dimming of 6 edge-lit LEDs is carried out, the dimming blocks cannot be clearly divided, but the dimming function is realized by compensating for the diffusion characteristics of light on the light guide plate. Even for darker images, the dimming can only be dimmed by about 1/4, so the dimming effect is not obvious. However, if the optical characteristics of the light guide plate and the configuration of the LED can be optimized, the low power consumption effect of dimming can be further improved. In the future, this dimming technology may also be adopted for edge-lit LED backlights.

Few people may be able to compare and distinguish the images of white LED backlight LCD TVs from those of CCFL backlight LCD TVs. However, if the adoption of LED backlights can improve their image as "environmentally friendly products", then it will be of great significance for companies to adopt LED backlights. In addition, the luminous efficiency of white LEDs is expected to increase year by year, so it is also a major advantage to be able to formulate plans for low power consumption in the future. With this in mind, the speed at which LCD TVs are equipped with white LED backlights should exceed expectations.