All posts tagged light

How Does PenTile RGBW Save 40% of the Power?

The power in an LCD primarily goes into the LEDs in the backlight. The problem is that a great deal of light is lost between those LED and your eyes. Losses occur in channeling the light from the LEDs to a light guide and more is lost in diffusers to make that light look uniform behind the LCD panel. Light is lost due to internal reflections even before hits the LCD. About half of the light is lost in the polarizers on the display cell. More is lost in trying to go through opaque cell structures like the FETs at each subpixel. Stillmore is lost in the color filters associated with each subpixel. In the best of cases 10% of the light makes it from the backlight to your eyes. For high resolution panels it can be less than 5%.

Since backplane FETs can only be made so small, the higher the resolution of the display the poorer the ratio between open area where light is transmitted through a subpixel and the total area of the subpixel that includes the FET and the buss bars. Each subpixel is also surrounded by a black matrix to prevent the backlight from photoactivating the subpixel FET, keeping it from turning on when you don’t want it to.

Color filters work by passing some color and absorbing all of the rest. Those other colors are just turned into heat.

1. In a PenTile RGBW there are one-third fewer subpixels used to create same number of pixels. That allows each subpixel to be one-third larger to pass that much more light to your eyes. In a display with 300 dpi it is a significant factor. So, this helps to fix the problem with aperture ratio.

2. Another  part of the savings  comes from the use of clear subpixels that pass the white light from the backlight nearly unaffected. Since some much content is white or pastel, this becomes very important. This helps improve on the losses through color filters.

3. Additionally, PenTile RGBW displays analyze each image for peak luminance and for highly saturated colors to minimize the backlight with Dynamic Backlight Control (DBLC). This is similar to content adaptive backlight control, but also examines saturated colors to optimize the choices between power savings and maintenance of high luminance saturated color. This takes advance of the natural occurrence of white to reduce color filter loss and enable less clipping artifact than is seen in RGB LCDs with CABC.

When it comes to a tablet 40%* can be a substantial saving. PenTile displays may look a little different than RGB stripe panels in some circumstances, but 40% is a number that is big enough that it is difficult to ignore when making a high resolution display product.

*  based upon JEITA usage model