LCD is the race to win, to HDTV, the dominant display technology. According to DisplaySearch, in 2007, the market for LCD (liquid crystal diode) television to an estimated $ 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 TV is a slight selective filter. It is not itself emit light, but selectively filters lightthe display back. Most HDTVs have a single sheet of plastic or light-emitting or side lighting with fluorescent lamps to provide the backlight. Both techniques are difficult to control.
HDTV
Many consumers focus on the resolution of the screen when you select a high-definition (HDTV). Is HDTV 720p, 1020i or 1020P? However, if a group of experts, the SMPTE (Society of Motion Pictures and Television Engineers), which recently ranked the importance of the screenResolution, is in fourth place. The contrast ratio SMPTE Rank, color saturation, color temperature and grayscale first display resolution more important. The Imaging Science Foundation reached a similar conclusion. backlight is the key component to improve contrast and grayscale.
It 'important that a system can adjust the height of the LCD backlight, and preferably, this function automatically. This improves the image contrast. Areduced backlight reduces power consumption and also prolong the life of the lamp, the power used and the life of the lamp is connected directly to the brightness of the backlight in combination. A lamp with a life of 50,000 hours at 6 mA, only 30,000 hours in duration, if the current is 7 milliamps, only 1 mA above (example: Sharp Electronics LCD).
Another important factor in the choice of lighting is the light of tolerance. Blur occurs when there is rapid movement in the planning,such as sports. If the picture is changing rapidly, the pixels can delay the response. Effective engineering backlighting can significantly reduce this strobing the backlight, so that each pixel is no longer necessary. Examples of this technique are the Apture Philips and the Samsung is LED Motion Plus. "
Since the light
With side lighting, lighting in the back of the LCD panel is found, and create on each side for key lighting. ToUniform light, a diffuser between the lights and the back of the optical filter. Most LCD systems, the use of cold cathode using the light side (CCF) for the lamps. This technology offers a very bright 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 intensity of light can be varied locally, and can watch the light side irregular. SomeCCF lamps contain mercury. This is an 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 Lighting
Most of the backlight is designed with a single sheet of electroluminescent plastic. These dishes are old (although the improvements in this area have reduced this problem). Electroluminescent backlight paneluse phosphors to produce colored light. Demonstrates how to use this technique, thin and light, providing an even distribution of light.
The main disadvantages:
limited period of 3,000 to 5,000 hours of bright half (2-3 years at a rate of 5 hours of operation per day). The intensity of light can not be changed locally.
A LED backlight
LED backlighting uses an array of LEDs that can be independently to provide a very good control. In this configuration, a largeNumber of LEDs are mounted uniformly behind the display. improvements in LED brightness are more practical for backlighting. NEC pioneered this technology with their monitor, 2180WG. Other companies such as Samsung, have recently versions of this technique. This should push prices down (the Samsung model costs less than 1 / 3 the price of a comparable NEC).
This system has a local dimming technology and can reach dynamic contrast ratio of 1,000,000:1. TrueIf the black levels (the "Holy Grail" of LCD) can be achieved by shutting down a pixel of light. This can eliminate the typical gray-black screen for many LCD HDTVs. The groups of LEDs can be controlled locally to produce more light increasing the brightness when necessary.
The problem with white LEDs is that their spectrum is not ideal for photographic reproduction, because they are actually blue LEDs with a yellow phosphorus above. Their color spectrum has two peaks, onein blue and yellow on the other. White LED based on a group of red, green and blue are ideal for RGB color filters of the LCD and may result in more saturated colors. Sony system TRILUMINOS "LED backlighting is an example of this technique.
Sometimes, these HDTVs a series of LEDs at the top and bottom of the screen. This improves the brightness and color reproduction, and allows almost complete uniformity across the display.
LED backlights are much moreefficient than alternative techniques. And since the LED-backlit waste less energy, generate less heat that must be managed with air conditioning. LED backlights offer a long life of more than 50,000 hours (more than 25 years of service at a rate of 5 hours per day).
Systems with LED backlight can not show well in a typical retail environment. Typically, the screens are more reflective, in order to achieve the high contrast ratio, and then a bright showroom canDo not flatter this technology. In a typical less enlightened, this problem should not be so obvious.
Engineering concerns
Electrical engineering is simple with LED backlighting. Cold Cathode Fluorescent Lamp (CCF) requires a high voltage AC (1500 AC), at startup, and the operating voltage of 700 VAC or more. When the lamp is new it may take to start a lot less stress, but increase with age, the voltage requirements of the rule, a designer makes the problem. ALight panel requires a voltage of 100 VAC @ 400 Hz
An inverter (to create VAC) is required for both CCF and electroluminescent panels to work with a direct current. 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 life of the lamps.
use the systems LCD with LED backlight voltage to low, usually in the 12or 24 VDC. This results in a small, simple and reliable. LED backlight systems must be well chilled or sustain their performance. The LEDs generate less heat than bulbs CCF, but the heat is very concentrated. The high temperature operation will shorten the life of the LED and shifts their spectrum of light, reducing the luminance output.
OLED
A new technology is that it is about the future of his hearing Organic LED (OLED). This technology has a completely differentbacklight technology, it is not necessary. For this reason, they draw much less power. And because there is no backlight, an OLED system has a viewing angle greater than an LED system. An OLED display is much thinner than an LCD display. The response time for OLED is faster than normal LCD monitor. An average of 8 to 12 milliseconds response time is normal for an LCD compared to 0.01 milliseconds response time for OLED.
Sony has introduced a 11 "HDTV at the ConsumerElectronics Show in Las Vegas. The new 11 XEL-1 TV Sony as is "." It 's very thin (10.1 ") and currently sells for $ 2500 Samsung has shown a 31" OLED TV 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 technology very promising. Toshiba plans to sell 30 "OLED display in 2009. Samsung announced that sell HDTV wide-screen OLED2010th
OLED displays have been used for some time in digital cameras, cell 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 cheaper than LCD or plasma, in the sense that it should not be so expensive. Remember that the first large LCD and plasma displays are much more expensive when they wereintroduced.
Summary
HDTV and LCD monitor with LED backlight array-are now the concept of choice, because they have better image quality while saving energy. The ability to locally control the power of light is the key to achieving high levels of contrast.
backlit LCD HDTV
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