OLED TV Provides Superior Viewability
Advances in design and manufacturing are making OLED TVs a very appealing option.
by David Choi
TVs have evolved to offer bigger screens, higher resolutions, slim and light designs, and overall better picture quality. LCD-TV technology in particular has achieved market dominance with outstanding picture quality and a slim footprint. However, the design of an LCD TV will always be based on the fundamental structure of a transmissive LC panel illuminated by some type of backlight system. The performance of this system, while continuing to achieve incremental improvements each year, will always be constrained because it cannot self-emit light in the same way that a phosphor or OLED panel can.
OLED technology provides new solutions by overcoming the fundamental structural limitations of LCD technology. OLED TV, for which the latest generation of advanced designs was first introduced in early 2013, is based on a much simpler structure of self-emission from the pixel matrix surface and can therefore reproduce more natural colors and better picture quality than an LCD TV (see comparisons of key features in Table 1).
OLEDs are composed of self-luminous organic light-emitting diodes that form each pixel. Because every pixel emits its own light, color contrast is optimized. In addition, an OLED can produce perfect blacks and an infinite contrast ratio with deeper and richer colors because there is no light leakage from a backlight. Even under typical living-room lighting conditions of 200 lux, OLEDs have better contrast because the reflection of an OLED screen is typically lower than that of an LCD screen. The LCD screen may have higher luminance at white, but OLED’s darker blacks will provide better contrast.
The outstanding broadcast picture quality of OLED TV highlights its superiority. With a pixel gray-to-gray-level response time of more than 5,000 times faster than that of an LCD TV, OLED TV also delivers smooth images of fast-moving events, such as soccer games, that are completely life-like because they are blur-free.
The Ultimate Display
In LCD panels, color saturation and brightness decrease in low-gray-scale scenes as the color gamut deteriorates. This is because color bleeding increases in dark scenes due to light leakage between the pixels. In addition, gray-level tracking between the three primary colors is typically not uniform at low gray levels, adding to color shift at very low gray-scale scenes. For example, reds in the low gray scale appear more washed out because the color gamut deteriorates toward white color coordinates due to light leakages from adjacent green and blue subpixels.
However, OLED TV provides vivid colors in any scene because it maintains consistent color gamut even as the gray level changes. Therefore, food looks more delicious and skin-tone colors are more life-like. It can even produce colors that are outside of the current broadcast color gamuts such as BT.709 (Fig. 1).
Fig. 1: Color-gamut maintenance is shown in all gray levels at BT.709 coverage of the CIE1976.
These results are shown in a recent study of color theory by Hongik University’s Color Research Lab (this is a thesis in progress, with an expected release date of December 2014.) According to the survey, color preference for OLED TV is 2.4 times higher than for LCD TVs and viewers surveyed mentioned that OLED TV is more “vivid,” “warm,” and “comfortable,” and provides more “life-like” colors.
Effective Curvature
Because an OLED TV has a wide viewing angle and no light leakage, it delivers consistent picture quality and color performance from any angle. In the case of a typical 55-in. VA-type curved LCD TV viewed from a distance of 2.1 m, the color wash becomes noticeable from an angle of 22° from the center. While other LCD types may perform better or worse in terms of color wash, OLED technology will still perform better at wider viewing angles. This forces people watching TV to gather together in the middle, but with a 55-in. curved OLED TV people can watch from any angle in the room and enjoy the same high picture quality with crisp and vivid colors (Fig. 2).
Fig. 2: The above schematics illustrate how curved OLED TVs offer a viewing angle that allows more people in a room to enjoy a positive viewing experience.
Manufacturing and Flexibility
As is generally known, manufacturing yields have proved a challenge, but LG has succeeded in improving yield rate and scalability by working with oxide TFTs and WRGB patterning technologies. The company has been improving the yield rate for OLED TV about twice as fast as it was able to in the initial stages of LCD-TV development. LG is now achieving satisfactory yield rates that are enabling lower production costs.
LG Display is building a new OLED manufacturing line, the world’s largest Gen 8 line, with a monthly capacity of 26,000 input glass sheets. Once completed, it will make it easier to produce large-sized and ultra-high-resolution OLED panels while making the cost of a OLED TV more affordable, setting the stage for a mass consumer market.
In addition, LG is also developing transparent and flexible OLED displays, which emphasize the natural advantages of OLED technology. The company rolled out 18-in. flexible and transparent displays in July 2014 and has been developing larger and higher-resolution displays that are transparent as well as flexible. We are confident that by 2017, we will successfully develop an UHD flexible and transparent OLED panel of more than 60 in., which will have a transmittance of more than 40% and a curvature radius of 100R.
In the shorter term, OLED TV has demonstrated high picture quality and stunning design since its launch. It’s been a challenging road, but yield has reached the point at which additional commercial launches are a reasonable expectation. •