backlit LCD HDTV

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) TVS was estimated at $ 27.4 billion €. LCD TV shipments rose more than expected 52% year over 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. Is not itself emit light,but selective light filters through the exhibition back. Most HDTVs are either a single sheet of plastic or luminescent numerals side lighting with fluorescent lamps to provide backlighting. Both techniques are difficult to control.

Many consumers focus on the resolution of the screen when you select a high-definition (HDTV) system. HDTV is 720p, 1020i, or 1020p? However, when a group of experts, the SMPTE (Society of Motion Pictures and Television Engineers), which recently ranked the importance ofScreen resolution is fourth. SMPTE Rank contrast, color saturation, color temperature and grayscale before the screen resolution in importance. The Imaging Science Foundation reached a similar conclusion. backlight is the key component to improve contrast and grayscale.

It 'important that a system for LCD backlight, adjusts the level, preferably, performs this function automatically. This improves the contrast ofImage. Furthermore, a reduced backlight brightness also reduce energy consumption and extends 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, only a life of 30,000 hours, when the current is 7 milliamps, only a higher milliamp (example: Sharp Electronics LCD).

Another important factor in the choice of backlight is the consideration of "uncertainty". Blur occurs when there is rapidMovement in programming such as sports. When the situation changes quickly, may put the pixels in response. Effective backlighting system engineering, this can significantly reduce the stroboscopic backlight, so the individual pixels remain lit longer than necessary. Examples of this technique are the "Apture Philips and Samsung" LED Motion Plus. "


First, the lighting is the rear panel at the rear of the LCD, and on each side forCreate button illumination. For the light uniformly, a diffuser between the lights and the rear of the optical filter module is located. Most systems that use LCD cold cathode fluorescent side lighting use (CCF) lamps. This technology provides a white light. The life of the bulbs is usually between 10,000 and 20,000 hours (6-12 years at a rate of 5 hours of operation per day).

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

The main disadvantages:

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

conventional backlight

Most of the backlight is designed with a single sheet of electroluminescent plastic. These plates can age (if the improvements have reduced this areathis issue). electroluminescent backlight panel uses colored phosphors to generate light. Displays with this technique, thin and light and provide uniform distribution of light.

The main disadvantages:

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

LED backlight

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

This system offers local dimming technology1,000,000:1 dynamic contrast ratio can reach. True actual black levels (the "Holy Grail" of LCD) source reached off of a pixel of light. This can eliminate the black-gray image typical of many LCD HDTVs. Groups of LEDs can be controlled locally to generate more light increasing 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 LED, blue, and are based on a group of red and green lights are ideal for RGB color filters of the LCD and can cause saturation of colors. Sony "TRILUMINOS" LED-backlight system is an example of this technique.
Sometimes, these high definition televisions, a number of LEDs on the top and bottom of the screen. This enhances the brightness and color reproduction and enablesalmost complete uniformity across the display.

LED backlight are much more efficient than alternative techniques. And since the LED-backlit display produces waste less energy, less heat to be operated with air conditioning. LED-backlit display offers a long life of more than 50,000 hours (more than 25 years of employment at a rate of 5 hours per day).

Systems with LED backlight can not show well, in a typical retail environment. Typically, screens, something reflectiveachieve high contrast ratio, and then, lit showroom may not flatter the technology. In a typical environment less enlightened, this problem should not be so obvious.

Engineering concerns

The electrical engineering is easier with LED backlight. Cold Cathode Fluorescent Lamp (CCF) requires a high AC voltage (1500 VAC) at startup and operating voltages of 700 VAC or more. When the lamp is new, may take much less voltage to start, but with agerequirements of growing tension in general make it difficult for designers of the problem. A luminous panel requires a voltage of 100 VAC @ 400 Hz

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

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


A new technology isThe consultation on the future of Organic LED (OLED). This technology has a completely different backlight technology, we need not be. For this reason, they draw much less power. And because there is no lighting, OLEDs have a wider viewing angle of an LED system. An OLED display is much thinner than an LCD display. The response time of OLED is faster than normal LCD screens. An average of 8-12 millisecond response time is normal for an LCD comparedto 0.01 milliseconds response time for OLED.

Sony has introduced a 11 "HDTV at the Consumer Electronics Show in Las Vegas. The new 11" Sony TV "as" XEL-1. It 'very thin (10.1 ") and currently sells for $ 2,500 a Samsung 31" OLED HDTV with 1080p resolution at an exhibition in Asia in November. LG, Toshiba, Matsushita (Panasonic), and others are investing hundreds of millions of dollars to develop this extremely promising technology. Toshiba expects to sell a30-inch OLED display in 2009. Samsung has announced that sell big-screen OLED HDTVs in 2010.

OLED displays have been used for Some time in digital cameras, cell phones and other devices with relatively small panels, because they are very energy efficient, which is very important for mobile devices.

In theory, OLED displays, plasma is cheaper to manufacture or LCD, that is, should not that expensive. Remember that the firstLCD and plasma displays are much more expensive when they were introduced.


HDTV LCD monitor with LED backlight array is now the concept of choice, because they have better image quality and saving energy. The ability to control local power light is the key to achieving high levels of contrast.

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~ by lcdhdtva on September 10, 2010.

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