by Jin S. Kim
LG Electronics just unveiled its 55-inch ‘OLED’ TV at CES. I put OLED in quotes because it’s not the OLED we know. Most of us have experienced OLED through Samsung’s Galaxy line of smartphones. Regardless of RGB-stripe or PenTile Matrix the OLEDs work in the same way: they emit both light and color. A red OLED phosphor emits red light when electrons are pumped through it. Same goes for green and blue. This is exactly what you see on this type of OLED display. WOLED is different.
WOLED stands for White OLED. Each pixel is made up of red, green, blue OLED sub-pixels to generate a white pixel. I am uncertain whether those sub-pixels are tuned separately, but I’m guessing not. Before I was wondering what LG Display meant by vertical accumulation. I think I know now: The three OLED diodes are stacked vertically, not side by side like a typical OLED display. The red, green, and blue light output is vertically mixed to generate white light. Because the three OLED diodes are vertically arranged each pixel should be small enough to pack 1920×1080 or more on a 55-inch sized display. Brightness is probably controlled at the pixel level. So think of WOLED as the ultimate local dimming backlight with pixel-level brightness control. Next, color.
A WOLED display generates color by using a color filter. The downside of using a color filter is light absorption of about 70% on a typical LCD. LGE’s announcement mentions “4-Color Pixels” and I believe that’s code for RGBW. This is not implemented at the OLED level but only at the color filter level. The white is absolutely necessary because a 55-inch WOLED TV will require a tremendous amount of power to generate enough brightness that is equivalent to a 55-inch LCD TV. The white portion of the color filter, which does not absorb any light at all, will help to brighten up the WOLED display while reducing power consumption. RGBW implemented on a LCD panel would result in washed out colors because there is no way to completely shut off the white sub-pixel, but with the pixel-level brightness control on a WOLED the white portion of the color filter can be completely turned off making blacks completely black.
LG Display has pushed the concept of the local dimming LED backlight to its theoretical maximum. Using OLED technology brightness is controlled at pixel level. Vertically stacking the OLED diodes mitigates the problems associated with differential aging. And by using a RGBW color filter power consumption is lowered. The 55-inch OLED TV by LGE does not use exactly the same OLED technology we are used to, but with WOLED we get extremely thin displays, absolutely black blacks, and superb contrast. But there are just three lingering questions.
First, power. RGBW reduces power consumption, but how much power will a 55-inch WOLED TV consume? Second, how long will WOLEDs last? Third, what’s the price?