End the confusion of wide color gamut: LED backlight technology analysis

After grayscale response time and dynamic contrast , the focus of LCD display technology in 2008 will shift to color gamut , which is a consensus among all industry insiders. However, there are still very few wide color gamut products available on the market, and the price is relatively high. Ordinary consumers do not know much about color gamut.

The so-called color gamut determines the color richness of a display. As we all know, CRT monitors and LCD monitors are based on three primary colors. The colors displayed by the monitor are all partial sets of the three primary colors, but there is no way to express all the colors of visible light. The color gamut value represents the color range that the monitor can display. The larger the color gamut, the richer the color that can be displayed on the display screen, and the more colorful the color.

For LCD monitors, all major manufacturers are committed to improving the color gamut of LCD monitors. At present, the color gamut values ​​of mainstream LCD monitors are about NTSC70%, while wide color gamut LCD monitors need to reach more than NTSC90%. Since the liquid crystal itself does not emit light, but relies on the light through the backlight to display the image, its color gamut range is mainly affected by the backlight source. The wide color gamut LCD monitors on the market mainly achieve a higher color gamut range by improving the composition of the fluorescent material of the traditional CCLF (or adding a layer of coating), making the light it emits "whiter" and more stable, so as to achieve the purpose of improving the NTSC color gamut. Since this method is not technically difficult to implement and the cost will not increase too much, it has been supported by many manufacturers. However, it must be seen that this method is not the best choice after all. With the help of this technology, the color gamut range of the LCD monitor is difficult to exceed NTSC100%. So is there any way to fundamentally solve this problem? At present, LED is the only answer!

The best answer to wide color gamut: LED light-emitting diodes

The current consensus in the industry is that using LED backlight is the best way to improve the color gamut of LCD monitors. The so-called LED (Light Emitting Diode), that is, a light-emitting diode, is a semiconductor solid- state light- emitting device . It uses a solid semiconductor chip as a light-emitting material. When a forward voltage is applied to both ends, the carriers in the semiconductor recombine to cause photons to be emitted to generate light. LED can directly emit red, yellow, blue, green, cyan, orange, purple, and white light. This type of LED backlight technology has long been used on laptop screens and LCD TVs , but it has not been used much on desktop LCD monitors.

As mentioned above, the liquid crystal of the LCD monitor itself does not emit light, but relies on the light from the backlight to display images, so the LCD backlight template plays a decisive role in the color gamut. The current mainstream CCFL (cold cathode backlight) is limited by the light emission range and cannot allow the LCD monitor to achieve a wide color gamut display range. Therefore, the color gamut range of the current mainstream LCD monitors is only about 70% of NTSC. Even if an improved design is used to allow it to have a larger color gamut range, the effect is not very ideal, and it may also result in a reduction in the life of the lamp tube.

In view of the shortcomings of CCFL (cold cathode fluorescent lamp), LED light emitting diodes have been placed with high hopes. Compared with CCLF cold cathode fluorescent lamps, LED light emitting diodes have advantages such as wide color gamut, adjustable white point, high dimming rate and long life. Currently, there are mainly two types of LED backlight sources: feedback type LED backlight source and combined type LED backlight source.

In terms of color, which is of most concern to everyone, since the LED backlight source can be dispersed by a lightguide and then reflected by a reflector to achieve a uniform brightness , the software that comes with the device can fully control the color backlight, which means that there is no need to compensate for the shortcomings of the lamp tube, and a truly complete white light source effect can be achieved. In addition, with the help of built-in sensors and circuits, users can also adjust the backlight in SpectraView according to their needs, which means that the colors are richer and can provide a color range that ordinary LCDs cannot present. At present, the color gamut range of LCDs using LED backlights can reach more than 110%.

Three major advantages of LED light emitting diodes

In addition to solving the wide color gamut problem, LED light-emitting diodes have more advantages than CCFL cold cathode backlights. The first one is environmental protection. In LCDs that use CCLF cold cathode fluorescent lamps as backlight sources, one of the main elements that cannot be missing is mercury, which is the familiar mercury, and this element is undoubtedly harmful to the human body. Although manufacturers have tried their best to reduce the mercury content in fluorescent tubes, completely mercury-free fluorescent tubes will bring some new technical problems, and there is no prospect of realization for the time being. On the contrary, the advantage of LED backlight sources is that they are completely mercury-free and conform to the fashion of green environmental protection.

In addition to being environmentally friendly, LED backlights are also very energy-saving, and their power consumption is lower than that of CCFL cold cathode backlights. The internal drive voltage of LEDs is much lower than that of CCFLs, and their power consumption and safety are better than CCFLs (CCFLs have relatively high AC voltage requirements, reaching 1,500 to 1,600Vac at startup and then stabilizing to 700 or 800Vac), while LEDs only need 12 to 24Vdc or lower voltage to work. In addition, although the luminous efficiency of CCFLs is not inferior to that of LEDs, since CCFLs are scattered light, a lot of light is wasted during the luminous process, which makes LED light appear more efficient.

In addition, the service life of LED backlight is longer than CCFL. Generally speaking, the rated service life (half-brightness) of different CCFLs is between 8,000 and 100,000 hours, while the rated service life of LED backlight can reach about twice that of CCFL. Of course, the service life of LED backlight is also affected by heat dissipation management.

Current Status of LED Backlight LCD

As the best choice to replace CCFL cold cathode fluorescent tubes, LED light emitting diodes are not widely used in desktop LCD monitors at present. It can be said that they are still in the initial stage. However, judging from the product strategies of major manufacturers, LED backlight LCDs will emerge in large numbers in the second half of 2008.

In terms of panels , Samsung Electronics announced in early 2007 that it would start producing 24-inch LCD panels using LED light sources . It also said that it could match the quality of high-level TV pictures, and the color gamut could reach 111% of the National Television Standards Committee (NTSC), which is the so-called true wide color gamut. In addition to large-screen LCDs, Chi Mei also launched 19- and 22-inch RGB LED backlight panels in early 2007 and shipped them to Acer and ViewSonic. Later, AUO also released a 20.1 -inch LCD panel using LED backlight . It is believed that BenQ, which has a close relationship with AUO, will be the first to get this type of LED panel.

In terms of products, as a promoter of wide color gamut LCD monitors, Samsung officially launched its first LCD with LED backlight as early as the beginning of 2007. The model is Samsung SyncMaster XL20, and its color gamut reaches 114%. At that time, the listing price in Hong Kong was HK$15,990. Of course, this product is aimed at professional users. In addition to Samsung SyncMaster XL20, the 19-inch Acer AL1917L (color gamut value is 117%) is also a product of early 2007. Recently, the most noteworthy is that ViewSonic launched the first 22-inch LED backlight LCD monitor with a wide color gamut of 118%. VLED221wm is mainly aimed at users with high requirements for color, such as artists, multimedia editors and players. This product is expected to be listed in February, and the estimated price is US$788. In addition, AOC, a global LCD factory, also stated that it will release products with LED backlight in the second quarter of this year.

It can be seen that major manufacturers have already started to take action on the research and development of LED backlight LCDs. According to industry insiders, in the second half of 2008, LED backlight LCDs will begin to emerge in large numbers and become the main choice in the market.

Although LED backlight LCD has a larger color gamut range, we must also note that consumers' acceptance of wide color gamut LCD monitors needs to be further strengthened. From the current situation, some users have reflected that after comparing wide color gamut LCD monitors with ordinary LCD monitors, although they feel that the colors of wide color gamut LCD monitors are richer and brighter, they feel that the richness and brightness are a bit fake. In addition, the price issue is also the main factor restricting the market acceptance of wide color gamut LCD. Of course, it is undeniable that as a new generation of LCD monitor focus technology, the emergence of LED backlight will undoubtedly give us more choices and lead us into a new horizon.