Even though ‘LED TV’ is simply marketing buzzword, its advantages outweigh its drawbacks
An increasing number of TV vendors, including Sony, Sharp Samsung, and LG, are launching their so-called "LED TV" products on the market. But in fact, LED TV is not a completely different product to LCD TV – it is, in essence, an LCD TV that adopts LED backlighting technology.
The biggest difference lies in the backlight technologies adopted – traditional LCD TVs use CCFL backlight (cold cathode florescent lamps), while the new generation of LCD TVs use LED (Light-Emitting Diode) backlights. And because of the difference between LED and CCFL backlighting technologies, it generates the difference in contrast, energy consumption, profile thickness, and the production cost in their respective TV sets.
LED-backlit LCD TV is not without its drawbacks, but its advantages outweigh its drawbacks; moreover, LED backlit TV has already become the future trend of LCD TVs, such technology cannot be replaced easily in the short run.
LEDinside explores the true features of LED TVs through the following aspects:
1. The conception of the term ‘LED TV’
The biggest promoter behind the grand hype of LED TV is Samsung, which began to promote the LED-backlit LCD TVs as early as 2007, when they coined the term ‘LED TV.’ Thereafter, other vendors such as Sony, Sharp, and Toshiba, have also begun to launch LED-backlit LCD TVs, and naturally adopted the term ‘LED TV’ either intentionally or passively. Even though using the term ‘LED TV’ to market the LED backlit LCD TV may mislead consumers to believe that the ‘LED TV’ is a new type of TV, the term effectively promotes the visibility of LED backlit TVs, and its definition is logical to a certain extent. However, under stricter definition, it would be more appropriate to use the term ‘LED-backlit LCD TV’.
Whether it is the mainstream CCFL-backlit LCD TVs, or the increasingly popular LED-backlit LCD TV, both require light bars to cast light onto the LCD panel, to display the color and contrast of the image to viewers. Similarly, this applies to LCD monitors and notebook monitors.
In the past, plasma TVs and OLED TVs (Organic Light Emitting Diode television) which were favored in the market for some years for they emit light and eliminate the need for backlight. After the screen is powered, each pixel on the panel emits light.
2. The main purpose of using LED backlight is its energy-saving attributes
As discussed in our previous LED TV feature story, ‘The Energy Saving Challenge of Large-Size TVs – LED TV’, according to ENERGY STAR specifications, LCD TVs larger than 50inch simply do not meet the energy saving standards, regardless of any enhancement in their energy saving features. The Version 4.0 specification requires that 46inch and 50inch TVs offer a saving of 50 percent than models currently on the market. From a market perspective, only TVs based on LED technology have the potential to be ENERGY STAR qualified under the Version 4.0 specification.
One of the main reasons for the adopting the LED backlight is the energy-saving attribute. LED backlight modules consume 30~50% less power than its CCFL-backlit alternatives of the same luminous efficacy. In terms of unit light source, LEDs ‘theoretically’ generate higher lumens per watt (lm/w) than that of the CCFL. Currently, some specially-formulated CCFL backlights offer similar luminous efficacy to that of LED backlighting. However, with the continuous improvement of LED luminous efficacy, upgraded CCFL no longer poses threat to LEDs. Furthermore, there is another advantage to LED backlight modules – the instant switch of on and off, contrast control, and optimized energy efficiency, which makes LED backlights more energy-efficient thank CCFLs. The difference is even more pronounced when compared to plasma TVs – the power consumption is LED TV is three times as energy efficient as plasma TV.
3. The secondary purpose of using LED backlight is its eco-friendliness
After the EU released the ROHS directives, countries across the globe became more conscious of eco-friendliness of materials used in electronic products. The environmental directive states that display devices require low mercury content, in an effort to reach mercury-free stage, completely eliminating the use of mercury. There are CCFL backlight products which contain extremely low levels of mercury, however, to be completely mercury-free, it would be more appropriate to adopt LED backlighting.
As for the eco-friendliness of the production process of CCFL backlight modules and LED backlight modules – it is still controversial, but for the ultimate usage purpose, not only is LED backlighting more eco-friendly, it is also relatively more energy-efficient.
4. The third purpose of using LED backlight – to enhance the contrast
LED TV "claims" it offers higher contrast ratio due to the difference in the light source – Direct Illumination-type LED Backlight LCD TV offers a ‘local dimming’ feature, which allows adjustments of a specific dimming level on any particular block of the LCD screen, allowing clearer contrast across different blocks, therefore, higher contrast ratio for the entire image.
When displaying black on direct type LED TVs, the LEDs behind the black block can be turned off, showing a perfect black. This feature also allows some vendors to use another marketing buzzword, claiming that their products achieve ‘dynamic contrast’ of 100,000:1. This, in reality, is simply another buzzword; such high contrast ratio is implausible.
As there is no local dimming technology in CCFL backlit screens, its backlight is achieved through the combination of CCFLs and a light guide plate, brightness adjustments spans over the entire screen. Therefore, the only way to enhance brightness contrast is through changing the colors.
There is another type of LED backlight source: the Edge (side-edge) type LED backlit TV, (which has no local dimming function) will be discussed below.
5. Two main types of LED backlighting – direct type and Edge Type
There is significant difference between direct type and edge type LED backlighting, in terms of light source, cost, and in their retail prices. The former is the most common type adopted by TV makers when LED-backlit LCD TV was introduced – the uniform distribution of LEDs over the entire LCD panel allows the light source to be transmitted uniformly across the entire screen, making the image more delicate and vivid. The downside is, direct type backlighting uses more LEDs compared to that of edge type.
The advantage of direct type backlighting is its individual blocks of backlight modules. In theory, the brightness of each LED can be independently controlled, but such circuit design is not cost-effective. In practice, the screen is sectioned into multiple blocks, and the brightness of each block can be adjusted independently.
A large-sized direct type LED backlit TV is lit by thousands of LEDs, therefore, the cost is extremely high. In particular, in the early stages when the LED TV has just been launched, RGB tri-color LED was used to improve the color rendering index, (making colors more vivid). The costs of such models are inevitably high. Recently, industry players have been adopting the less expensive white-LEDs as backlight; despite its poor color rendering index in the beginning, substantial improvement has been achieved..
As for the edge type LED backlight, LEDs are configured on the edges of the LCD screen; when light is emitted from the LED backlight module, it is dispersed to the central region of the screen through a light guide plate, providing sufficient amount of backlight for the overall LCD screen.
There are two advantages in edge type LED backlight: 1. more cost-effective – through the reducing the number of LEDs used; 2. slimmer profile – as the LED modules are configured on the edge of the LCD panel, and not behind it, it reduces the overall thickness of the screen, making them slimmer than the direct type ones.
6. The drawbacks of direct type LED backlight – blooming and energy consumption
As mentioned earlier, the advantage of direct type LED backlight is local dimming, which offers better dynamic contrast, and more vivid image on the LCD screen. But are there any drawbacks?
In addition to the relatively higher costs, there are several drawbacks.
Blooming – even though local dimming offers higher contrast in image, but during the process of image shift, i.e. adjusting the bright block to dark ones, the gray scale intensity in the adjacent regions will be reduced, hence creating the ‘blooming’ effect. The extent of this drawback varies across different vendors and models. In theory, for direct type LED backlight modules, if the density of LEDs configured behind the LCD screen is higher, or if there are more local dimming blocks, it will minimize the occurrence of blooming. However, with edge-type LED backlit TV, blooming would not be an issue. (Though it has other drawbacks which will be discussed later).
Another drawback is its high power consumption – as direct type uses more LEDs than edge type ones, it consumes more power, though, on the whole, power consumption of both are still lower than that of CCFL backlit LCD TV.
The other one is the viewing angle of the LCD screen itself, and this problem becomes more obvious when viewing the direct type LED TV. It is a commonly accepted fact that the viewing angle of LCD screen is quite narrow, and adopting the LED backlight in fact intensifies the issues, rather than improves it. Viewers are to center themselves in front of the screen to see the "best" image. If the viewer watches the LED TV in a location that is slightly off-center, there will be a significant difference in the image. This issue of narrow viewing angle exists both horizontally and vertically, and there is also a difference in standing and sitting positions; however, the extent varies on a case by case basis.
7. The shortcomings of Edge type LED backlight – poor image uniformity
As mentioned earlier, the biggest advantage of edge type LED backlit TV is its ultra-slim profile and its low production cost (although this cost advantage is not necessarily reflected in its retail price). And the drawbacks?
Currently, the biggest drawback of edge type LED backlight is its poor uniformity. Even though the edge type LED TV is thinner, and uses fewer LEDs, the light is dispersed to the center through a light guide plate, which makes the edges of this type of TV brighter than the center of the screen. This drawback is seen in both all-black and all-white image test. Moreover, the temperature on the edges of the TV screen is higher than that of the center, as LED lights produce heat.
Insights from LEDinside: continuous technological and cost improvement in both LED backlight technologies
Although there are drawbacks in both types of LED backlighting methods, novelty attracts consumers, and LED TVs will undoubtedly become increasingly popular in the future. The goal of many global manufacturers is to improve the blooming, thickness, and cost of direct type LED TV (through optimizing the LED configuration, enhancing luminous efficacy, and lowering LED prices), and to improve the image uniformity of the edge type LED TV (through improving the luminous efficacy, and reducing the number of LED light bars from 4 to 2, ultimately, aiming for a 1 light bar configuration).
At this stage, there is no absolute answer to whether direct type or edge type LED TV is better; however, according to LEDinside, backed by consumers’ growing preference of slim TVs, sales of edge type LED TVs will outshine that of direct type ones, and their prices will be more reasonable, too. The direct type LED TV will also be well-received for its superior performance in image quality, particularly among consumers who seek high-end audio-visual equipment.
In the near future, the price gap between LED-backlit LCD TVs and CCFL ones would be narrower; at that time, LED TV will gain widespread popularity, securing a stable and sustainable capacity in the LED industry.
Sharp’s demonstration of LED TV: