Steve explains: A full brightness white pixel uses 5.8 times more juice than a black pixel. That doesn't mean you could ever increase your battery life by 5.8 times. That's for 2 reasons. The first is that no one spends all day staring at a fully white screen and because no one would every want to switch to a fully black screen! The second is that the screen isn't the only thing using power. . .
Let's look first at changing wallpaper. I've got no idea what the brightness of the average wallpaper is so I'm just going to go with a 50% grey wallpaper for the purposes of this comparison. When the grey wallpaper is used the average pixel brightness is 47%. For the black wallpaper it's 15%. So by changing, I've reduced average pixel brightness by 32%. If I spent all day on the home screen I'd save . . . about 11%.
There is another technique to save the battery life. Many apps offer you the choice of using a standard black-on-white theme, or a white-on-black theme. Steve found that by switching that app's theme, he could save nearly 23% more battery when reading RSS feeds.
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