How color of screen affects power consumption

Probably everybody who has laptop knows that decreasing backlight reduces power consumption, but this is not only way to manipulate screen power.
There was a time when I interested in construction of LCD monitors and how they work, then I realized that power consumption depends on color and its hue. How is this possible, I will tell you. The most rear layer (called backlight) emit white light which passes through polarizer next glass layer next liquid crystal next second glass layer and finally second polarizer oriented perpendicular to the first one. Now we will focus on liquid crystal which is surrounded on two sides by electrodes. Unless we applied voltage on the electrodes, molecules of liquid crystal lay the perpendicular to the light (polarized before) and light will be rotated through an angle of 90 degrees, therefore it can passes through next polarizer. If we applied voltage on the electrodes, light isn't rotate (molecules lay the parallel to the light) and can't passes through second polarizer so pixel will be black. Summarizing, brighter colors uses less power or colors with higher value per each RGB bit uses less power.

Diagram of LCD monitor

Research:
Hardware: 15.4'' TFT WXGA Toshiba TruBrite

Research for screen filled with colors white and black.

Backlight

The easiest way to save power is decrease brightness of your screen. Difference between the highest and the lowest level is a couple of watts but it also depends on screen's diagonal. Worth of recommendation is simple but useful program called xbacklight using RandR extension. It has text interface but you can use it in applets, other programs or commonly assign to keyboard shortcut.


Research:
Hardware: 15.4'' TFT WXGA Toshiba TruBrite
 
Below you can see comparison of power consumption when backlight brightness is set to 100% and 0%.


Short description of using xbacklight:

COMMAND
       xbacklight [option]
OPTIONS
       -get   Returns the current backlight brightness
       -set [percent]   Sets backlight brightness 
       -dec [percent]   Decrease backlight brightness
       -inc [percent]   Increase backlight brightness
EXAMPLES
       xbacklight -set 75
       xbacklight -inc 10
       xbacklight -dec 5