When I was at my local Verizon today looking at phones I couldn’t help but notice that many of the choices for wallpaper were not optimal for saving power, and were chosen for reasons that had more to do with the graphics designer’s idea of what looked good.
Most people now understand that for an OLED display it only consumes power when and where the screen is lit, so a good screen saver would be one that is mostly black.
When it comes to an RGB stripe LCD the best way to save power is to turn the display off when the panel is not in use since the backlight is otherwise turned on. However, for images that do not have lots of white brightness, Content Adaptive Backlight Control (CABC) in today’s RGB stripe displays will also turn down the backlight and increase the transmission of the LCD.
How about for a PenTile RGBW LCD? In these displays there is a clear (white) subpixel, which together with improved aperture ratio increases light transmission to save power. In addition there is an algorithm which we call Dynamic Backlight Control (DBLC) which continually analyzes image data for highly saturated color with high luminance. The reason for this is that all RGBW displays must pay attention to an effect known as Simultaneous Contrast Error. Simply stated, if you put a bright and highly saturated color on the screen at the same time as a bright white, it is necessary to supply more power for the display so that the eyes and brain will perceive the correct shade of saturated color. This is especially true for yellow. For PenTile displays, to combat this effect, the backlight brightness is turned up to increase the luminance of the colored subpixels while the white level is turned down tomaintain the desired perception of color to make a perfect looking yellow. In other words the worst case power consumption for a PenTile display is when you are displaying more than a minimal amount of highly saturated colors, regardless of whether it is red, green, blue or a combination of these colors. This is true even if the image is largely dark. The best power consumption, other than a totally black screen, would be to use unsaturated colors or simply black and white. The worst case power consumption for OLED is the best case power consumption for a PenTile RGBW display.
So if you have one of the new Motorola smartphones with a PenTile RGBW LCD display, you might want to replace the wallpaper featuring saturated colors with one that is either black and white, or colors of less than 50% saturation. The power benefits should soon be apparent.