LED TV

LED TV

INTRODUCTION

LED TV (Light-emitting diode television) is a term used by Samsung electronics and other consumer electronics companies to describe its line of LCD (liquid crystal display) TVs that use LED backlighting. The term LED TV is disputed and the complaint is that the display is not composed of 100% LEDs and so should not be called LED TV.
LEDs in their current form are much too large to be individual pixels on a conventional television. The use of a true LED display is therefore reserved for much larger screens in sports grounds and other commercial locations.
LED-backlit LCD TVs do differ from conventional LCD TVs in some important areas:
• They can produce a very bright image with greater contrast and deeper blacks compared with LCD TVs.
• With Edge-LED lighting they can be extremely slim. Current models on the market are just over 1 inch thick.
• They consume much more power. About 40% less compared with an LCD TV of a similar size.
• They can offer a wider colour gamut, especially when RGB-LED backlighting is used.

HISTORY

LED History
From the early 1900s, scientists have been discovering ways to generate light from various materials. In 1907, Henry Joseph Round discovered that light could be generated from a sample of Silicon Carbide (SiC). For the next 50 years, scientists continued to discover the light emitting properties that exist with some compounds. In the 1950s, studies around the properties of Gallium Arsenide (GaAs) paved the way for the first official LED discoveries that soon followed.1
LED research began in the early 1960’s, primarily at Bell Labs, Hewlett Packard (HP), IBM, Monsanto, and RCA. Gallium-Aresenide-Phosphide (GaAsP) provided the basis for the first commercially available red LEDs in 1968 by HP and Monsanto. In the early 1970s, the use of LEDs exploded with new applications such as calculators and watches by companies like Texas Instruments (TI), HP, and Sinclair. Other applications such as indicator lights and alphanumeric displays soon became the mainstream use for LEDs and continued to be so for many years.2

LED TV HISTORY

Sony was the first manufacturer to produce a commercial LED-backlit LCD television with the Qualia KDX-46Q005 in 2005. However, Samsung was the first to coin the term "LED TV" on their 2009 range of Luxia LED edge-lit televisions. Previously, Samsung had also integrated LED backlights into the 40, 48, 52, and 57-inch versions of their LN-T81F series in 2007 and their A950-series in 2008. Sony, in addition to RGB LED backlighting (still used on 46 and 55-inch versions of the BRAVIA KDL-XBR8 series), also introduced the first flat-panel monitor to use edge-LED lighting in 2008. In 2008, Sharp introduced the AQUOS LC-XS1US series, 52 and 65-inch HDTVs to use LED back-lighting, and plans to release LED edge-lit HDTVs in the second half of 2009. While LED TVs are still expensive to manufacture, Vizio will release the VF551XVT, the cheapest HDTV to use LED backlighting. It will retail for $2199.99. LG has also released their own LED-backlit HDTVs. LED backlighting is also becoming common in computer monitors. Examples of monitors that use LEDs are Apple's 24" and 30" cinema displays, the Sony BRAVIA KLV-40ZX1M, and Dell's G2210 and 2410 monitors.

LED TV

When a product has become commoditized and its price is regularly dropping and its profit margins are getting ever-thinner, how can a company boost its sales and raise its prices?
That’s what Samsung has done with its new line of LCD TVs using LEDs to illuminate the screen. In its print advertising and on its Web site, Samsung calls the new range simply “LED TVs.”
They are not LED TVs. Calling them such makes as much sense as calling its existing line of LCD televisions Cold Cathode Fluorescent Lamp TVs, or CCFL TVs, after the lighting technology that they use.
Whatever its validity, Samsung’s decision to drop “LCD” was a smart marketing move. After all, “LED” is the acronym du jour, a technology that’s all the rage as a new, perhaps revolutionary lighting source. It’s as emotive a term as “HDTV” and “digital” were in their heydays.
But it’s also confusing consumers. An industry colleague told me that in a recent trip to a big-box retailer, he overheard several friends asking what type of TV they were watching. One said it wasn’t LCD or plasma, it was an LED set.
More accurately, it was an expensive LCD set. LED-backlit LCD TVs can cost as much as twice their standard LCD or plasma counterparts. Is the extra money worth it, even if you can afford it?
Here are the answers to some questions you may have about LCD TVs using LED backlighting.
Up until now, LCDs used fluorescent tubes to light the screen. As a result, LCDs have trouble creating deep blacks. That’s because fluorescent tubes are always on, and some light leaks through to the front of the display even when a part of the image is supposed to be black. A lack of deep blacks reduces the perceived sharpness of the set’s image.
Also, fluorescents lack a wide range of colors; hence, color saturation is limited.
It’s an LCD TV that uses LEDs to illuminate the display. There are two ways to do this: either by placing LEDs across the entire back of the display, or by placing LEDs just around the perimeter, which is called an “edge lit” display. Both techniques use less power than plasma TVs and LCD TVs lit with fluorescent tubes.

WORKING

Controlling the thermal stability of the LED die is critical to the performance and stability of LED illumination and reliability. The LED architecture inherently produces light from all sides and surfaces of the PN structure in a lambertian distribution (uniform distribution into a 180 degree hemisphere). While this might seem efficient, most of this light is actually absorbed into adjacent die, the mounting substrate, or other surfaces of the LED assembly. This absorption results in an increased thermal loading of the entire LED assembly. This heat must be addressed to obtain maximum light output and reliability. Additionally, for applications that require imaging of the light energy to a small display device (e.g. DLP® HDTV), any light that is emitted outside of the system etendue is not useable and only adds to the heat and overall power loading. Controlling this absorption, shaping the light to match the system etendue, and maximizing the thermal efficiency to extract heat from the die are all critical to increasing the light output and usability of the LEDs.
For traditional applications, LEDs are commonly driven in CW (continuous wave – 100% duty cycle) mode. For high brightness applications, however, this is not as desirable. Since the average temperature of the PN junction determines both the light output and lifetime of the LED, it is often more efficient to drive the LEDs with a smaller duty cycle. With a smaller duty cycle, the LEDs can potentially be driven to higher current loads to increase the overall light output while maintaining a lower average temperature of the PN junction. The challenge with this, however, is that the driver circuitry must be able to generate fast switching waveforms, switching large currents in as short a time as only a few microseconds. This certainly presents some challenges for the design of the LED power driver. But, solutions have already been developed with performance that easily meets these requirements.
Another challenge that results from higher thermal loading is that of color shift. As the PN junction changes temperature, the output wavelength of the light can shift by as much as 10nm or more. This color shift obviously impacts the color point for that color, but also impacts the white point for the system since each of the colors are mixed to create white. Fundamentally, to stabilize this color shift, the LEDs must either be run at a lower power or maintain extreme thermal stability. However, with the implementation of some form of system feedback and proper power control algorithms, the stability of the white could be preserved while maintaining high brightness efficiency.

TI has developed a DLP HDTV system to take advantage of LED illumination with brightness performance that is nearly equivalent to lamp based systems. By utilizing the latest generation of high brightness LEDs and implementing a unique feedback system, it is now possible for DLP HDTV designs to enjoy the benefits of LED illumination. Figure 5 illustrates the basic optical configuration of this system.

Figure 5 – DLP

Utilizing a unique feedback algorithm, TI has demonstrated that any color shift variations that affect the white point can be controlled to a tolerance beyond what the eye can detect.
The current DLP® products implementation with LED technology utilizes a TI DSP component to process system information in real time, offering superior stability over a wide range of operating temperatures while maximizing brightness and reliability.

SCREEN

Samsung uses a term LED TV (light emitting diode television) for describing LCD (liquid crystal display) TVs which utilizes LED Backlighting. LED TV is a controversial term effectively used for the advertisements between Samsung and its competitors. But the complaints of the competitors are, LED TV produces a display of 100% LEDs and which is not compromised in this. LEDs in their current form are much too large to be individual pixels on a conventional television.
In order to capture some of the hype around O-LED TVs, Samsung has chosen to brand their LED-lit range of LCD TVs but still except for the Sony XEL-1 they are not commercially available.
LED-backlit LCD TVs do differ from conventional LCD TVs in some important areas:

1. LED televisions can produce bright image and deep blacks (doesn’t work for Edge-LED). 2. The LED-TV can be extremely slim with Edge-LED lighting. 3. LED televisions offer lower power consumption. 4. Especially when RGB-LED backlighting is used, they also offer a wider colour gamut.
After our comparison between Plasma TV and LCD TVs, today we’ll discuss about the latest buzzword in the Display Industry - LED TVs and how it compares with the traditional LCD TVs. The LED TVs which are being touted as better display to the traditional LCDs are actually using a new backlighting technology that improves the display of LCD TVs by producing better contrast and black levels combined with better power efficiency. Traditional LCD TVs use CCFL (Cold cathode Fluorescent Lamps - these use the same technology like the plain tube lights) to light the displays. The LCD panel in front of it subtracts lights from the white lights to produce various colors on the screen. This cheaper backlights are replaced with white LEDs (Light Emitting Diodes) in case of LED TVs to make it more slim and gain some other advantages. Here is a comparison between them.

TECHNOLOGY

TV manufacturers can use an LED backlight instead of the standard Cold Cathode Fluorescent Lamps (LCD-CCFL) used in most LCD televisions. It is important to distinguish this method of backlighting a conventional LCD panel, from a true LED display, or an OLED display. Televisions described as 'LED TVs' are vastly different from the self-illuminating OLED, OEL or AMOLED display technologies
There are several methods of backlighting an LCD panel using LEDs including the use of either White or RGB (Red, Green and Blue) LED arrays positioned behind the panel; and Edge-LED lighting, which uses white LEDs arranged around the inside frame of the TV along with a special light diffusion panel designed to spread the light evenly behind the LCD panel.
An LED backlight offers several general benefits over regular CCFL backlight TVs, typically including lower power consumption and higher brightness. Compared to regular CCFL backlighting, there may also be benefits to color gamut. However advancements in CCFL technology mean wide color gamuts and low power consumption are also possible. The principal barrier to wide use of LED backlighting on LCD televisions is cost.
The variations of LED backlighting do offer different benefits. The first commercial LED backlit LCD TV was the Sony Qualia 005 (introduced in 2004). This featured RGB LED arrays to offer a color gamut around twice that of a conventional CCFL LCD television (the combined light output from red, green and blue LEDs produces a more pure white light than is possible with a single white light). RGB LED technology continues to be used on selected Sony BRAVIA LCD models, with the addition of 'local dimming' which enables excellent on-screen contrast through selectively turning off the LEDs behind dark parts of a picture frame.
Edge LED lighting was also first introduced by Sony (September 2008) on the 40inch ZX1 BRAVIA. The principal benefit of Edge-LED lighting for LCD televisions is the ability to build thinner housings (the ZX1 BRAVIA is as thin as 9.9mm). Samsung have also introduced a range of Edge-LED lit LCD televisions (described incorrectly as "LED TVs") with thin housings. Edge-lighting however is at risk of a loss of screen uniformity compared to back-lighting.
LED-backlit LCD TVs are considered a more sustainable choice, with a longer life and better energy efficiency than plasmas and conventional LCD TVs. Unlike CCFL backlights, LEDs also use no mercury in their manufacture. However, other elements such as gallium and arsenic are used in the manufacture of the LED emitters themselves, meaning there is some debate over whether they are a significantly better long term solution to the problem of TV disposal.
Because LEDs are able to be switched on an off more quickly than CCFL displays and can offer a higher light output, it is theoretically possible to offer very high contrast ratios. They can produce deep blacks (LEDs off) and a high brightness (LEDs on), however care should be taken with measurements made from pure black and pure white outputs, as technologies like Edge-LED lighting do not allow these outputs to be reproduced simultaneously on-screen.
The figure below shows various LED TV’s:

COMPARISON

Black Level / Contrast
LCD TV: The backlight is constantly lit in case of traditional TVs. The LCD panel has to block all those lights to make it pure black which is not 100% efficient. This is why a powered on LCD TVs always show some whites on its screen.
LED TV: In case of edge lit LCD TVs the backlights are placed at the edges which make it slimmer without any additional advantages to produce better Black Levels or better contrasts. However, the LED matrix lit TVs do produce better contrast and black levels by using some sort of intelligent lighting technology. Behind the black spot on the screen can be turned off to get deep black levels and better contrast ratios.
Conclusion: LED TV is a clear winner here.
Refresh Rate / Response Time
Refresh Rate and Response Times are properties of LCD Panel and nothing to do with the backlighting.
Conclusion : No one wins. It’s a tie.
Viewing Angle
LCD TV : LCD TVs traditionally suffer from poor viewing angles and this is a real shortcoming over their main competitors : Plasma TVs.
LED TVs : The LED TVs are able to produce better viewing angles due to their nice backlighting technology.
Conclusion : LED TV wins here.
Color Accuracy
LCD TV: Color Reproduction depends solely on the LCD Panel.
LED TV: The tri colour backlit LCD TVs can change the backlighting colors. This can produce more accurate colors.
Conclusion: White backlighting LED TVs does not have an advantageous position but the tri color backlighting LED TVs are surely a winner.

Power Consumption
LCD TV: Uses less power than Plasma TVs.
LED TV : Uses nearly equal power like the plasma TVs in same screen sizes.
Conclusion: LCD TVs win on their power efficiency.
Price
LCD TV: The LCD TVs are produced in much larger number than the LED TVs, so they have a price advantage.
LED TV: These TVs are sometimes twice more costlier than the traditional TVs.

Conclusion:The LED TVs have a price toll for their better picture quality.

ADVANTAGES

An indication of the depth and purity of black levels produced by this new wave of LED TV's can be gleaned from the manufacturers claimed contrast ratios (in a nutshell the difference between the brightest white and darkest black that can be produced onscreen). Always to be taken with a pinch of salt, LED TV's will however invariably claim a contrast ratio of around 1,000,000:1 rather than a figure closer to 50,000:1 for traditional LCD TV's.
LED TV's consume much less power than your the traditional LCD TV's; About 40% less compared to a similar sized screen.
Certain implementations of LED technology produce much slimmer screens.
LED TV's offer a greatly expanded range of colors (gamut), particularly when RGB-LED backlighting is used.
With the removal of lead from the manufacturing process along with longer life, they are considered more environmentally friendly.
Ultimately, LED TV's produce sharper on screen images with a greater range of colors, faster response times along with superior contrast ratios.

DISADVANTAGES

Huge price and high power consumption are the main disadvantages of the LED TV.

CONCLUSION

I am really happy to discuss with you about the LED TV. It is very much useful in the present world. Although it consume more power it give more clarity, better picture, comparatively good audio, etc. it very much small in size.
Even though it’s price is not affordable, new inventions are going on to reduce the power consumption and there by to reduce the price.

REFRENCE

Web Article, “A brief history of the Light Emitting Diode (LED)”, http://www.wavicle.biz/led_history.html