Continuing the discussion from Battery lifetime decreased since update v1.8:
I think this is a myth. Here is why:
Smartphones typically use one of two different display types, called OLED and LCD.
Now, this can be a bit confusing, but here is the difference:
Both types use LED (Light emitting diodes for illumination, however, their construction is different. In LCD (liquid crystal displays), a background light source is required, without it, the screen stays dark. The light from that source travels to an array of crystals in red, green and blue color, which depending of their configuration are more or less transparent. All fully transparent would be white, you get the idea? This is typically called LCD-Display, but TVs using an LED as backlight are marketed as “LED-Display” to differentiate against older models with CCFL backlight.
Why is all that important? Because with an LCD-Display, the vast amount of power is used by the backlight and only depends of the brightness of the screen, not the color displayed. That means, the power consumption should be the same, no matter what color your background or the content displayed is.
OLED displays do not need a backlight. Here the individual pixels of the screen are emitting light themselves. A complete black (“off”) pixel, does not use any power. Therefore, a dark colored background/interface uses less power that a bright one. This is why techniques like Microsofts Glance screen only work on OLED devices: By powering of most parts of the screen and only powering some pixels, these smartphones can display some content like time and date all-day without reducing battery lifetime much. This is not possible on LCD-type screens.
What does that mean for you? The Fairphone uses and LCD-screen, therefore the background of your smartphone should not affect the battery lifetime at all.