LCD is winning the race to be the dominant display technology for HDTV. According to DisplaySearch, in 2007, the market for LCD (liquid crystal diode) TVs was estimated at $ 27.4 billion euros. LCD TV shipments rose faster than expected 52% year on 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 LCD HDTV is a selective light filters. It is not in itself emit light, but selectively filterLight through the display from behind. Most HDTVs have either offer a single sheet of luminescent plastic or side lighting with fluorescent lamps for the backlight. Both techniques are difficult to control.
Many consumers focus on the screen resolution when selecting a High Def (HDTV) system. Is the HDTV 720p, 1020i or 1020P? However, when a group of experts, the SMPTE (Society of Motion Pictures and Television Engineers), recently on the importance of the screenResolution, so the fourth rank. The 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 key component for improving the contrast ratio and grayscale.
It is important that an LCD system allows for adjusting the height of the backlight, and preferably, this function automatically. This improves the contrast of the image. Areduced brightness of the backlighting reduces power consumption and extend the life of the lamp, as the power used and the lamp life is directly related to the brightness of the backlight in context. A lamp with 50,000 hours life at 6 mA may be a 30,000 hour lifetime, if the current 7 mA, only 1 milliamp higher (example: Sharp Electronics LCD) display.
Another important factor in the choice of the backlight is the light of the "fuzziness". Blur occurs when there is rapid movement into the programming,such as sport. If the picture changes rapidly, the pixels can lay in the reaction. Effective backlighting engineering can be a significant reduction of strobe the backlight, so the individual pixels will be no longer than necessary on. Examples of this technology are Philips' Aptura "and the Samsung" LED Motion Plus. "
Sidelight
With side lighting, the lighting on the back of the LCD panel is located, and create buttons on each side lighting. ToLight more uniform, a light diffuser between the lights and the rear of the optical filter module is located. Most LCD systems with fixed light use cold cathode fluorescent tubes (CCF) lamps. This technology offers a very bright white light. The lifetime of the lamps) is usually between 10,000 to 20,000 hours (6-12 years at a rate of 5 hours use per day.
The main disadvantage is that the intensity of the light will not vary locally, and side-light can not look uniform. SomeCCF lamps contain mercury. This is an ecological disadvantage.
The main disadvantages:
The intensity of light can not be varied locally. This leads to a lower contrast image.
The light is not uniform.
Some CCF lamps contain mercury.
Conventional backlight
Most of the backlight is performed with a single sheet of electroluminescent plastic. These plates can age (although improvements have reduced this problem in this area). Electroluminescent backlight panelused to produce colored light phosphor. Shows using this technique can be thin and light and provide uniform light distribution.
The main disadvantages:
Limited life span from 3000 to 5000 hours to half brightness (2-3 years) at a rate of 5 hours use per day.
The intensity of light can not be varied locally.
LED backlight
LED-backlit display uses an array of LEDs can be controlled individually to provide a very good control. In this configuration, a largeNumber of LEDs are mounted uniformly behind the display. Improvements in LED brightness, they have more practical for backlighting. 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 NEC monitor).
This system offers local dimming technology and a dynamic contrast ratio of 1,000,000:1 reach. Trueactual black levels (the "Holy Grail" of the LCD) will be reached by turning off a pixel source. This can eliminate the typical gray-black screen for many LCD HDTVs. Groups of LEDs can be controlled locally, so that produce more light, making the brightness when 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 at the top are. Their spectrum has two peaks on aA blue and another in yellow. White LEDs, which are based on a group of red, green and blue LEDs based on the RGB color filters, an LCD is ideal and can result in the saturated colors. Sony's "Tri-color LED backlight system 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 across the display.
LED-backlit display are muchefficient that 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 life of more than 50,000 hours (more than 25 years) use a rate of 5 hours per day.
LED backlighting systems can not show well in a typical retail environment. In general, the screens are somewhat reflective in order to achieve the high contrast ratio, and then a brightly lit showroom maynot flatter this technology. In a typical less-lit environment, this problem should not be so noticeable.
Engineering concerns
The electronics is simpler, with LED backlighting. Cold-cathode fluorescent (CCF) requires a high AC voltages (1500 VAC) 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, a designer complicates the problem. ALight box requires a voltage of 100 VAC @ 400 Hz.
Generate an inverter (to VAC) for both CCF and electroluminescent panels required 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 lamps automatically increase as the age, prolonging the life of the lamps.
LCD with LED backlight systems use low voltage DC, usually 12or 24 VDC. This results in a smaller, simpler and more reliable system. LED backlight systems must be well chilled or their performance may suffer. The LEDs generate less heat than CCF lamps, but the heat is very concentrated. Operation at high temperatures reduces the LED lifetime and shifts its spectrum of light, while reducing output luminance.
OLED
A new technology that you will hear is about the future of organic light emitting diode (OLED). This technology has a completely differentBacklight technology, he does not need this book. For this reason, they draw much less power. And because it's no backlight, an OLED system has a larger angle than an LED system. 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 millisecond response time is normal for an LCD, compared with 0.01 millisecond response time for OLED.
Sony introduced a 11 "HDTV at the ConsumerElectronics Show in Las Vegas. The new 11 "Sony TV is called the" XEL-1 ". It is very thin (1 / 10") and currently sells for $ 2500 Samsung showed a 31 "OLED HDTV with 1080p resolution at a trade show in Asia in November. LG, Toshiba, Matsushita (Panasonic), and others are investing hundreds of millions of dollars to develop this extremely promising technology. Toshiba has plans to sale of 30-inch OLED display in 2009. Samsung has announced that they sell large OLED screen in HDTV2010th
OLED displays 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 favorable than LCD or plasma displays, which means that it should not be so expensive. Note that the first large LCD and plasma displays were much more expensive than they firstintroduced.
Abstract
LCD HD televisions and monitors with LED-array backlight are now the concept of choice because they have a better image quality, while saving and electricity. The ability to locally control light power is the key to high contrast ratio.
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