As you may already know, small OLED (Organic Light Emitting Diode) panels have been introduced to consumers in several forms for several years, and at CES 2012 LG and Samsung showed their 55-inches 1080p OLED HDTV prototype panels, both displaying stunning images and with prices said to be around $10,000 USD when available toward the second part of 2012, however, the OLED panels have not yet appeared at local stores, although they are expected soon in 2013. At least LG announced at CES 2013 panel availability for the first quarter in the US, at a higher price: $12,000.
As I covered in this article, LG’s WOLED HDTV uses a white OLED design and implements passive 3D technology displaying half resolution images per eye both eyes viewing simultaneously using low cost 3D glasses, while Samsung’s Super OLED HDTV uses a more classic RGB design and implements active-shutter 3D technology that renders full resolution images per eye displayed in alternate fashion.
If you are interested to know more about the OLED technology, a colleague publication has released The OLED Handbook - A Guide to OLED Technology, Industry and Market.
As you may be aware, OLEDs of various colors have been developed with sufficient efficiency using fluorescent and phosphorescent materials for the commercialization of not only OLED TV panels, but also to generate white light for general lighting, back light for LED displays, and other display applications.
In order to create white light the organic materials of primary colors (red, green, and blue, or alternatively blue and yellow) have to be excited simultaneously. Incorrect excitation of more than one organic species may cause color stability problems.
Uneven longevity between organic materials may also produce unintended colors as a panel ages, and phosphorescent blue has been known to have a shorter lifespan compared to fluorescent blue and compared to the other phosphorescent colors, although the blue’s lifespan is now much longer than a few years back. Apparently LG has used a fluorescent material for the blue and a phosphorescent material for the red and green, and if so the life span of all may have been equaled but I have no confirmation yet from LG of that, I asked LG Display in Korea last week at CES to provide me their official response.
LG’s OLED implements WOLED with a set 4 sub-pixels, of which 3 sub-pixels are used to create colors with color filters and 1 extra sub-pixel is used to produce white light without using a filter, the set of 4 sub-pixels conforms a single pixel of image on the screen.
Although not publicly confirmed by LG, all the 4 sub-pixels appear to be made of a stack of organic materials of either a) blue/yellow colors, or b) the three RGB colors. The stack of organic color materials is used to create white light by each of the 4 sub-pixels, rather than to directly create the color a sub-pixel may need to display.
When a pixel in the screen needs to display a particular color the white light of each of its sub-pixels is passed thru the color filters located in front of the sub-pixels, and that produces the intended color.
This is an approach that is rather similar to LCD technology, whereby light is coming from the back of the panel and color is created by the filters at front (while the liquid crystals regulate the light passing thru).
However, although WOLED still uses filters each WOLED sub-pixel is capable to generate and control its own light, which can be turned off at the pixel level to render blacker blacks and higher contrast than typical LCD panels with edge (or back) illumination designs, which are known to produce uneven light distribution across the panel, that is more noticeable when displaying a plain white image, showing the corners with a different illumination than the center of the screen (although multiple zone LED designs tend to mitigate that problem).
Samsung uses the classic RGB design of OLED, by which each of the 3 sub-pixels emits its own red, green or blue color, without using filters. If the pixel needs to show full white it blends the colors of the 3 sub-pixels to create white light, but if a pixel needs to show just red it should not need to use (shorting the life off) the blue and green sub-pixels. Unless black has to be displayed, LG’s WOLED uses all the color stacks of the sub-pixels constantly to produce white light regardless of the final color displayed by the pixel thru the color filters.
Until both companies disclose the details of how their pixel technology is used on their OLED panels, it appears that Samsung’s RGB design uses more efficiently the blue sub-pixel organic material (known for its restricted durability relative to the other two colors) because it is only used when is actually needed to display blue, not to generate white light to show a non-blue color with a filter (WOLED).
Additionally, not needing color filters at the front of the Samsung OLED panel potentially produces an image with true emissive benefits, like plasma and CRT, such as maintaining image quality even when viewed at wide angles (a weakness of LCD beyond 20 degrees off center).
Although the OLED Handbook does not actually provide the comparative analysis mentioned above, a quick reading persuaded me to recommend it to consumers and industry professionals that would like to get a closer look at the OLED technology.
Ron Mertens, the author of “The OLED Handbook Guide to OLED Technology, Industry & Market, 2012 Edition”, is a software engineer that in July 2004 launched OLED-Info to offer daily news and resources for the OLED community, and has done a great effort to cover the OLED subject for manufacturers and industry professionals, while making the content easy to read for consumers,.
Here is the Table of Contents:
The book can be ordered in hard copy or pdf version.
Posted by Rodolfo La Maestra, January 22, 2013 7:51 AM