Black wallpaper on an AMOLED display: how much battery does it save?
A few weeks ago, we posted a selection of wallpapers ideal for AMOLED displays. The images in question had one thing in common – they were predominantly black – and that's not only because of the striking contrast achieved by screens of that type. It is a known fact that on AMOLED screens, pixels that are totally black draw no power at all. That is why putting a solid black wallpaper on such a display results in lower power consumption, thus improved device battery life. But at the end of the day, how much power would this save? Surprisingly, not as much as you'd expect.
To test how much battery life I could gain by switching to a black wallpaper, I gathered three phones with AMOLED displays that I had access to – the Samsung Galaxy S7 edge, the OnePlus 3, and the Nexus 6P. Then I set their screen brightness to a constant level – 200 nits when displaying a white image. Normally, a smartphone screen's brightness fluctuates below and above that point (if auto brightness is enabled, of course), but 200 nits is a reasonable average. Finally, I ensured that no background apps were interfering with my experiment.
My testing consisted of setting a series of 50 images as wallpapers and measuring what effect that had on power consumption. The average value of all 50 measurements served to show how much power each phone would draw with a typical wallpaper. Then I compared the figure against having a solid black image set as a wallpaper. I made a test using a solid white image as well, just to see what each phone's consumption would be in a worst-case scenario. Here's a chart with the results:
- On the Galaxy S7 edge: savings of about 1.2% battery charge per hour spent on the home/lock screen or 3.2% at best (if you switch from a completely white to a solid black wallpaper).
- On the OnePlus 3: savings of about 0.6% battery charge per hour spent on the home/lock screen or 4.5% at best.
- On the Nexus 6P: savings of about 1.4% battery charge per hour spent on the home/lock screen or 4.6% at best.