LCD is winning the race to be the dominant technology for HDTV display. According to DisplaySearch, in 2007, the market for LCD (liquid crystal diode) TV was estimated at 27.4 billion U.S. dollars to euros. LCD TV shipments rose more than expected 52 years% annually in the second quarter of 2008 just under 7.5 million units (79.8% of total sales of HDTV).

The LCD screen on an LCD HDTV is a selective filters light. Is not itself emit light,but selectively filters light through the display from behind. Most HDTVs offer their customers a single sheet of plastic luminescent or side lighting with fluorescent lamps for backlighting. Both techniques are difficult to control.

Many consumers focus on the resolution of your screen when you select a high-definition (HDTV) system. HDTV is 720p, 1020th or 1020P? However, when a group of experts, the SMPTE (Society of Motion Pictures and Television Engineers), recently the importance ofThe screen resolution, so the fourth. SMPTE Rank contrast ratio, color saturation, color temperature and grayscale, before the screen resolution in importance. The Imaging Science Foundation to a similar conclusion. Backlight is the essential component for improving the contrast ratio and grayscale.

It is important that a system of LCD allows you to adjust the height of the backlight, and preferably, this function automatically. This improves the contrast ofPicture. In addition, a reduced backlight also reduce energy consumption and prolong the life of the lamp, power used and the lamp life is directly related to the brightness of the backlight in context. A lamp with 50,000 hours of life at 6 mA can be a life 30,000 hours, if the current 7 mA, just above 1 milliamp (example: Sharp Electronics LCD) display.

Another important factor in the choice of the backlight is the light of the confusion "." Blur occurs when there is a rapidMovement in programming such as sports. If the situation changes rapidly, the pixels can put in the reaction. Engineering effective backlight can be a significant reduction of Strobe backlighting, so that the pixel is no longer required. Examples of this technology are Apture Philips' "and Samsung" LED Motion Plus. "

Lateral

With side lighting, lighting on the back of the LCD panel is located, and on each pageprovide lighting key. In the light more uniform, a light diffuser between the lights and the rear of the module optical filter is located. The majority of fixed systems LCD using cold cathode fluorescent light tubes (CCF) lamps. This technology offers a very bright white light. The lifetime of lamps) is usually between 10,000 and 20,000 hours (6-12 years at a rate of 5 hours per day.

The main disadvantage is that the intensity of light can not be variedlocally and light side one can not look uniform. Some CCF lamps contain mercury. This is one ecological disadvantages.

The main disadvantages:

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

Traditional backlight

Most of the backlight is performed with a single sheet of electroluminescent plastic. These plates can age (although the improvements have reduced this areathis problem.) Electroluminescent backlight panel 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 life span 3000-5000 hours to half brightness (2-3 years) at a rate of 5 hours per day.
The intensity of light can not be changed locally.

LED backlight

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

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

The problem with traditional white LEDs is that their spectrum is not ideal for photographic reproduction, because they are basically blue LEDswith yellow phosphorus at the top. 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 screen is ideal and can cause the colors saturated. Sony's "Tri-color LED backlight system is an example of this technique.
Sometimes, these HDTVs a set of LEDs on the top and bottom of the screen. This improves the brightness and color reproduction and enablesalmost complete uniformity across the screen.

LED-backlit display are much more efficient than alternative techniques. And since the LED-backlit waste less energy, generate less heat, which must be managed with air conditioning. LED-backlit display offers a long duration of more than 50,000 hours (more than 25 years), using a rate of 5 hours per day.

LED backlight systems, may not show well in a typical retail. In general, the screens being a little 'reflectiveachieve high contrast ratio, and later, a lit showroom may not flatter the technology. In a typical less enlightened, this problem should not be so obvious.

Engineering concerns

The electronics is simpler, with LED backlighting. Cold cathode fluorescent (CCF) requires a high voltage (1500 VAC) at startup and operating voltages of 700 VAC or more. When the lamp is new, so you can run a lot less tension, but with the age ofTypically increase voltage requirements, a designer complicates the problem. A window of light requires a voltage of 100 VAC @ 400 Hz

Generating an inverter (for VAC) for both the CCF and electroluminescent panels needed to operate with a DC power supply. This is a significant effort, cost, size and weight of the system. The best converter for this application allows the output voltage to the lights to automatically increase the age, extending the useful life ofLamps.

LCD with LED backlight systems use low voltage DC, usually 12 or 24 VDC. This translates into a smaller, the system simpler and more reliable. LED backlight systems must be well chilled or their performance may suffer. The LEDs generate less heat than bulbs CCF, but the heat is very concentrated. Operation at high temperatures reduce the life of the LED and shifts its spectrum of light, reducing light output.

OLED

A new technology that isfeel in the future is Organic LED (OLED). This technology is an entirely different technology backlight, does not need this book. For this reason, they draw much less power. And why is not illuminated, a system of OLED has an angle greater than a LED. An OLED display is much thinner than an LCD display. 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, comparedresponse time of 0.01 milliseconds for OLED.

Sony has introduced a 11 "HDTV at the Consumer Electronics Show in Las Vegas. The new 11" Sony TV called XEL-1 '. It is very thin (1 / 10 ") and currently sells for $ 2,500 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 technology very promising. Toshiba plans to sell a30-inch OLED display in 2009. Samsung said it sold large OLED full-screen HDTV in 2010.

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

In theory, OLED displays can be produced more favorable than LCD or plasma, which means that it should not be so expensive. I remember the firstLarge LCD and plasma screens are more expensive when they were introduced.

Abstract

HD LCD TV and monitors with LED-backlight arrays are now the concept of choice, because they have better image quality, while saving and electricity. The ability to control the power at the local level the light is the key to the high contrast ratio.

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