Common TV Types:
- CRT (Cathode Ray Tube)
- Plasma
- LCD (Liquid Crystal Display)
o CCFLs (cold cathode fluorescent lamps)
o LED-lit (Light emitting diode)
§ Rear Lit (LED TV)
§ Edge Lit
- OLED (Organic LED)
- ‘True’ LED
‘True’ LED TV
This is a kind of display where LEDs are the primary component that produces the images displayed, ie rather than using an LCD panel in the television, a matrix of LEDs is used to produce the images that are displayed. However as it stands ‘true’ LED TVs aren’t really possible at the moment because of the size of LEDs. The use of LEDs in this way is limited to very large screens for advertising and public events etc.
LCD TV
The LCD panel is a matrix of liquid crystal through which light must be passed from another source to make it visible. When an electrical current is applied to the LCD panel the light can be deflected and altered to make the colors and images visible to the viewer. An LCD panel does not produce light. Depending upon the light source LCD has two main types, i.e. CCFL & LED-lit. LED-lit LCD has further two types/configurations i.e. rear-lit LED and edge-lit LED.
LCD – CCFL
Up to this point the job of producing the light which makes the LCD panel images visible has been done by cold cathode fluorescent lamps (CCFLs). It is these fluorescent lamps which are now being replaced by LEDs.
There are two main issues with CCFL LCDs.
1- Sharpness: The inability of LCD TVs to produce truly dark black images. Producing perfect dark blacks is difficult if not impossible when using fluorescent lamps in LCD TVs. This because firstly the lamps must always be switched on, to produce areas of black on screen the light must be blocked by the LCD display so that it is not visible to the viewer. However this process is not perfect and some of the light leaks through making the blacks produced less than perfect. The result is the images on screen may seem slightly blurred or less sharp.
2- Colour Spectrum: Less than perfect color saturation (a limited range of colors). In relation to color, the quality of the light produced by fluorescent lamps limits the range of color (although since the early days of LCD TV this situation has been improved by producing more effective fluorescent lamps).
LED-lit LCD (LED TV)
Use of LED (light emitting diodes) in LED TVs is to provide the light source for the LCD panel. Hence an LED TV is still actually an LCD TV, be it one which uses LEDs for the back(rear) or edge lighting. Consequently a more accurate term to describe an LED TV would be LED-lit LCD TV.
LED-lit LCDs are available in two configurations:
1- Rear(back)-lit (Samsung brands it as “LED TV”)
2- Edge(side)-lit.
LED-Rear-lit LCD TV
LEDs are smaller electrical components when compared to the size fluorescent lamps or tubes. This means that they can be placed to the rear of LCD panels to create an LED rear-lit LCD TV. Many LEDs are used in a matrix to provide the light required to light the LCD panel.
Advantages LED-lit over CCFL LCDs:
1- Local dimming: LEDs can be individually switched on or off. This solves the problem of light leaking through the LCD display when black images are required, because rather than blocking the light through the LCD display the corresponding LEDs are switched off, this technique is known as ‘local dimming’. Dynamic contrast ratios of 2,000,000:1 is achievable through this technique.
2- Enhanced Colours: The advantage that the use of LEDs has brought to LCD TVs is the improvement in range of colors, this is known as “color gamut”. The inherent properties of LEDs mean that the light produced by them is ‘whiter’ (using Red, Blue, Green LEDs) than that of fluorescent lamps (to be specific the light produced has a broader spectrum). The practical result is that LED-lit LCD TVs are capable of producing a wider range of colors that consequently enhance the images displayed so that the pictures look more natural and intense to the viewer.
3- Power: LEDs are more energy efficient and so power consumption is improved by up to 40%, ultimately making them friendlier to the environment.
4- Reliability: LEDs are also said to be more reliable than fluorescent lamps and their performance does not degrade. Over time fluorescent lamps performance decreases as they become dimmer and they can eventually fail totally.
Issues/Disadvantages:
1- Cost: This technique is not quite so simple because it is too complicated and expensive to produce LED back-lit LCD TVs with enough LEDs that can be controlled individually.
2- Static Contrast: Practically TVs with up to approximately 1000 back LEDs can be produced and the LEDs are controlled in blocks rather than individually. The result is that when images of light and dark are simultaneously displayed (static contrast) a compromise is made because some LEDs are switched on for light areas and others are switched off for dark areas and therefore some light will leak into the blacks from adjacent areas of light.
LED-edge-lit LCD TV
White LEDs positioned around the rim(edge) of the screen which use a special diffusion panel to spread the light evenly behind the screen.
Advantage:
1- Thickness: The major advantage of using LEDs in edge-lit configurations is that because they are much smaller than fluorescent lamps the physical thickness of the television can be greatly reduced. Manufacturers such as Sony and Samsung have produced televisions that are only 1cm to 2.5cm in thickness. Hence Edge-lit LED TVs major advantage is that they are ultra thin and have slightly improved picture qualities.
2- Cost: Because the technology of edge-lit LED TVs is less complex they are however cheaper than rear-lit TVs.
Disadvantage (Compared to LED rear-lit):
1- Local Dimming: Due to placement of LED at the rim of screen, the benefits that comes from using LEDs in rear-lit LCD TVs (i.e. local dimming for improved blacks) is no longer applicable.
2- Rear-lit LED TVs use RGB LEDs (red, green, blue LEDs) and edge-lit LED TVs use white LEDs. The significance of this is that the RGB LEDs used in rear-lit TVs produce the whiter light that improves color gamut and the white LEDs used in edge-lit TVs produce a color gamut which is comparable to that of fluorescent lamps used in conventional LCD TVs.
Conclusion:
With the success that LED TVs have seen in 2009, the television industry seems to be heading in the direction where LED TV will become the mainstream television, replacing conventional CCFL-lit LCD TVs. Currently Samsung produces TVs with screen sizes available from 32 inches to 55 inches, Samsung plan to expand this range from 19 inches to 65 inches and so catering for a wider audience. Although Samsung is also continuing with its plasma TV range. Sony however is only going ahead with its LCD TV range. All computer/laptop TFT (thin film transistor) panels are also essentially LCDs.
Plasma TV
A plasma display panel (PDP) is a type of flat panel display common to large TV displays (80 cm or larger). Many tiny cells between just two panels of glass hold a mixture of noble gases (xenon, neon, and helium). The gas in the cells is electrically turned into a plasma which emits ultraviolet light which then excites phosphors to emit visible light.
Plasma displays can be produced in fairly large sizes—up to 3.8 m (150 inches) diagonally. The display panel itself is only about 6 cm (2.5 inches) thick, generally allowing the device's total thickness (including electronics) to be less than 10 cm (4 inches). Currently, plasma panels cannot be economically manufactured in screen sizes smaller than 32 inches. Plasma displays use as much power per square meter as a CRT TV
Advantages:
1- Slim profile.
2- Achieves better and more accurate color reproduction than LCDs (68 billion vs 16.7 million)
3- Produces deep, true blacks allowing for superior contrast ratios as compared to LCD.
4- Far wider viewing angles than those of LCD (up to 178°); images do not suffer from degradation at high angles unlike LCDs.
5- Virtually no motion blur, thanks in large part to very high refresh rates and a faster response time. (contributing to superior performance when displaying content with significant amounts of rapid motion)
Disadvantages:
1- Earlier models are susceptible to screen burn-in and image retention (newer models have green phosphors and built-in technologies to eliminate this)
2- Phosphors in older models lose luminosity over time, resulting in gradual decline of absolute image brightness (newer models are less susceptible to this).
3- Generally do not come in smaller sizes than 32 inches
4- Susceptible to reflection glare in bright rooms (due to use of glass to hold gases)
5- Heavier than LCD due to the requirement of a glass screen to hold the gases
6- Use more electricity, on average, than an LCD TV
7- Do not work as well at high altitudes due to pressure differential between the gases inside the screen and the air pressure at altitude.
8- More delicate to ship.
OLED TV - Future
OLED televisions, organic light emitting diode televisions to be exact, are the televisions of the very near future. OLED technology is far superior in so many different aspects, but it all comes down to one simple thing that put it ahead of the pack- backlighting. With the new OLED technology, there is no backlight to fail. Also, because there is no backlight to power up, operational costs are substantially slashed.
Without a backlight, the profile of an OLED television is much, much thinner than its comparable LCD or plasma counterpoint. The thickness can be taken down from inches to mere millimeters. In fact, OLED’s can be printed on just about any surface imaginable. The applications for this technology mean that very soon, televisions will be nothing more than flat, flexible, mats that can be rolled up and put away just like a poster.
The thin film that supplies the luminescence for an OLED television, is not only thinner than a backlight, it is also far more efficient because the pixels themselves actually emit the light. This important feature allows for true blacks (an LCD is never truly black because of the backlight) and vibrant, true to life colors that are the same no matter the viewing angle. There is no distortion even when the viewing angle is 180 degrees. Much better refresh rates are seen with this newer technology, and the fastest LCD at 2ms is crushed by the blazingly fast rates of less than .01ms that the OLED delivers. That’s 200 times better.
There are a few companies who are ready and willing to bring OLED televisions into the family rooms of the masses. Samsung, the front runner in the OLED industry, recently displayed both the first foldable screen made thinner than ever before seen, and the largest OLED television with an impressive 40 inch viewing area,
OLED televisions, thinner, brighter, more portable and more energy efficient are about to make both LCD’s and plasma televisions a thing of the past. One very interesting thing about the new OLED technology is that it has the potential to create transparent screens. Lukas’ ideas of futuristic screens in the popular movie trilogy (now a series) Star Wars can finally be realized with this amazing new technology. The next step with OLED televisions may even be flexible televisions that could be folded or even curved for a more genuine movie experience.
Reference:
http://www.sony-asia.com/productcategory/tvp-lcd-tv
http://www.samsung.com/mea_en/consumer/tv-audio-video/television/index.idx?pagetype=type
http://ledhdtvtelevisions.com/
http://hometheater.about.com/od/lcdtvfaqs/f/lcdtvfaq8.htm
http://reviews.cnet.com/4351-12658_7-6583301.html
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