power consumption depending on screen content

[Timo Juhani Lindfors]

Joerg Reisenweber <joerg at openmoko.org> writes:
> A completely white screen with ~40% backlight consumes same amount of power as 
> a completely black screen (-content) with backlight "dim" (=off)
>
> (=> a black screen eats as much power as a backlight set to 40%)
>
> (DUT: FR A7 SHR-U0808)

I wrote

http://iki.fi/lindi/openmoko/display-current-measurement1.pl

to test this. However, here white screen with 40% brightness consumes
significantly more than black screen with 0% brightness:

>dbg running echo 102 > /sys/class/backlight/gta02-bl/brightness
>dbg sleeping for 60 seconds for current to stabilize
>dbg taking 10 samples with 10-second delays
>dbg current now   102750, mean 102750.0000, deviation   -1.0000, range    0.0000
>dbg current now    99750, mean 101250.0000, deviation 2121.3203, range 3000.0000
>dbg current now    99750, mean 100750.0000, deviation 1732.0508, range 3000.0000
>dbg current now    91875, mean 98531.2500, deviation 4657.4034, range 10875.0000
>dbg current now    91875, mean 97200.0000, deviation 5012.9520, range 10875.0000
>dbg current now    91875, mean 96312.5000, deviation 4982.9396, range 10875.0000
>dbg current now    90750, mean 95517.8571, deviation 5011.1483, range 12000.0000
>dbg current now    90750, mean 94921.8750, deviation 4936.1718, range 12000.0000
>dbg current now   101812, mean 95687.4444, deviation 5157.0280, range 12000.0000
>dbg current now   101812, mean 96299.9000, deviation 5233.6376, range 12000.0000
>dbg running xset dpms force off
>dbg sleeping for 60 seconds for current to stabilize
>dbg taking 10 samples with 10-second delays
>dbg current now    48000, mean 48000.0000, deviation   -1.0000, range    0.0000
>dbg current now    48000, mean 48000.0000, deviation    0.0000, range    0.0000
>dbg current now    52687, mean 49562.3333, deviation 2706.0407, range 4687.0000
>dbg current now    52687, mean 50343.5000, deviation 2706.0407, range 4687.0000
>dbg current now    52687, mean 50812.2000, deviation 2567.1756, range 4687.0000
>dbg current now    62250, mean 52718.5000, deviation 5203.4787, range 14250.0000
>dbg current now    62250, mean 54080.1429, deviation 5961.7104, range 14250.0000
>dbg current now    62250, mean 55101.3750, deviation 6229.5975, range 14250.0000
>dbg current now    54562, mean 55041.4444, deviation 5830.0278, range 14250.0000
>dbg current now    54562, mean 54993.5000, deviation 5498.6935, range 14250.0000