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LCD is winning the race for the dominant display technology for HDTV. According to DisplaySearch, in 2007, the market for LCD (liquid crystal diode) TVS has been estimated at 27.4 billion euros. LCD TV shipments rose more than expected 52% a year in the second quarter of 2008 to nearly 7.5 million units (79.8% of total sales of HDTV).

The LCD screen on an HDTV LCD is a selective light filters. This does not itself emit light, but selectively filter lightthrough the display back. Most HDTVs have offered either a single sheet of plastic or light side lighting with fluorescent lamps for backlighting. Both techniques are difficult to control.

Many consumers focus on the screen resolution when choosing a high definition (HDTV) system. Does HDTV 720p, 1020i or 1020P? However, when a group of experts, the SMPTE (Society of Motion Picture and Television Engineers), recently the importance of the screenResolution, so the fourth. Ranking the SMPTE contrast ratio, color saturation, color temperature and grayscale before the screen resolution is important. The Imaging Science Foundation to a similar conclusion. Backlight is the key to improving the contrast ratio and grayscale.

It is important that an LCD system adjusts the height of the backlight, and preferably, this function automatically. This improves the image contrast. Areduces the brightness of the backlight helps reduce power consumption and extend lamp life, as the power used and the lamp life is directly related to the brightness of the backlight in its context. A lamp life 50,000 hours at 6 mA may be either a lifetime of 30,000 hours, if the current of 7 mA, only 1 milliamp higher (example: Sharp Electronics LCD) display.

Another important factor in choosing the backlight is the light of uncertainty. "Blur occurs when there is rapid movement in the lineup,like sport. If the situation changes quickly, the pixels can lay in the reaction. Engineering efficient backlight can be a significant reduction of strobe the backlight, so that individual pixels will only be required on. Examples of this technology are Philips Apture "and Samsung" LED Motion Plus.

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With side lighting, lighting at the rear of the LCD is, and create buttons on each side of the lighting. Tomake the lighting more uniform, a light diffuser between the lights and the rear of the optical filter module is located. Most liquid crystal systems with the use of fixed light cold cathode fluorescent tubes (CCF) lamps. This technology provides a strong white light. The lifetime of lamps) is usually between 10,000 and 20,000 hours (6-12 years at a rate of 5 hours of use per day.

The main disadvantage is that the light intensity does not vary locally, and May SidelightNon-uniform. Some CCF lamps contain mercury. It is an ecological disadvantage.

The main disadvantages:

The intensity of light can not be changed locally. This leads to an image of low contrast.
The light is not uniform.
Some CCF lamps contain mercury.

Conventional backlight

Most of the backlight is made with a single sheet of electroluminescent plastic. These plates can age (although improvements have reduced this problem in this area). ElectroluminescencePanel backlight using phosphors to produce colored light. Shows using this technique can be thin and light and provide uniform distribution of light.

The main disadvantages:

Limited lifetime from 3000 to 5000 hours to half brightness (2-3 years) at a rate of 5 hours of use per day.
The intensity of light can not be changed locally.

LED backlight

LED-backlit display uses an array of LEDs can be individually controlled to provide very good control. In thisConfiguration, a large number of LEDs are mounted uniformly behind the display. Improving brightness LED, they are more convenient for the backlight. NEC pioneered this technique with the monitor, which 2180WG. Other companies such as Samsung, have recently versions of this technology. This should push prices down (the Samsung model costs less than 1 / 3 the price of a comparable monitor NEC).

This system offers local dimming technology to reach and1,000,000:1 dynamic contrast ratio. True true black levels (the "Holy Grail" of the LCD) will be reached by turning off a source pixel. This can eliminate the typical gray-screen black for HDTVs many LCD. Groups of LEDs can be controlled locally, so that produce more light, making the brightness if necessary.

The problem with conventional white LEDs is that their spectrum is not ideal for photographic reproduction, because they are basically blue LEDs with yellow phosphorus to beHigh. Their spectrum has two peaks, one blue and one yellow. White LEDs, which are based on a group of red, green and blue LEDs based on RGB color filters, an LCD monitor is ideal and may result in saturated colors. Sony Tri-color LED system backlight is an example of this technique.
Sometimes, these HDTVs have a number of LEDs on the top and bottom of the screen. This improves the brightness and color reproduction and enables an almost complete uniformity in allDisplay.

LED backlit screen is much more effective than alternative technologies. And since the LED-backlit waste less energy, generate less heat, which must be managed with air conditioning. LED-backlit display offers a long lifetime of over 50,000 hours (over 25) use a rate of 5 hours per day.

Systems LED backlighting may not display properly in a retail point. In general, the screens are a bit more reflective, to achieve high contrast ratio, andSubsequently, an exhibition hall lit May not flatter this technology. In a typical environment of less enlightened, this problem should not be noticeable.

Engineering concerns

The electronics is simpler, with LED backlighting. Cold cathode fluorescent (CCF) requires a high voltage AC (1500 ACC) at startup and operating voltages of 700 VAC or more. When the lamp is new so they can run a lot less tension, but generally increase with age, the voltage requirements,Designer complicate the problem. A box of light requires a voltage of 100 VAC to 400 Hz

Generate UPS (VAC), both the RTC and electrical panels for the operation of a DC supply. This is a significant effort, cost, size and weight of the system. The best converter for this application allows the output voltage lights to automatically increase as the age, which prolongs the life of lamps.

LCD with LED systemsBacklight with low voltage, usually 12 or 24 VDC. The result is a smaller and simpler and more reliable. Systems LED backlighting should be properly refrigerated or performance may suffer. LEDs produce less heat lamps in the CCF, but the heat is very concentrated. Operate at high temperatures reduce the life of LED and shifts its spectrum of light, while reducing light output.

OLED

A new technology that you hear in the future is organic LED(OLED). This technology relies on a technology completely different backlight, it does not need this book. For this reason, they draw much less power. And because it's no backlight, an OLED system has an angle greater than a LED. An OLED display is much thinner than an LCD. The response time for OLED is faster than normal LCD screens. An average of 8 to 12 milliseconds response time is normal for an LCD, compared to 0.01 milliseconds for a response time of OLED.

Sonyintroduced a 11 "HDTV at the Consumer Electronics Show in Las Vegas. The new 11" Sony TV is called the "XEL-1". It is very thin (1 / 10 ") and is currently selling $ 2500 Samsung has shown a 31" OLED HDTV with 1080p resolution at a trade show in Asia in November. LG, Toshiba, Matsushita (Panasonic), and other investments are hundreds of millions of dollars to develop this extremely promising technology. Toshiba plans to sell a 30-inch OLED Samsung 2009thannounced that they sell large format OLED screen HDTV in 2010.

OLED screens are used for some time in digital cameras, mobile phones and other devices with relatively small panels, because they are very energy efficient, which is very important in portable devices.

In theory, OLED displays can be produced more favorably than LCD or plasma, which means it should not be so expensive. Note that the large LCD screen were first plasma screens and much moreexpensive when they presented for the first time.

Abstract

HD LCD TVs and monitors with LED backlight array is now the notion of choice because they have better image quality, while saving and electricity. The ability to locally control the light power is the key to high contrast ratio.