On most computer displays, such as the computer screen you’re probably reading this article on, using a black background won’t save you any battery life. No matter what color a pixel is – whether it’s dark black or blinding white – there’s a backlight at the back of your screen and it’s constantly outputting light. The black pixels block more of the backlight, but it’s still behind the black pixel, using power.
For many portable devices – including Apple’s iPhone – you can’t save any battery life by using a black background. Like on a computer’s LCD monitor, the iPhone’s backlight is constantly shining when the screen is on.
However, this doesn’t apply if you’re using a mobile device with an AMOLED (also known as Super AMOLED or OLED) display. OLED screens don’t have a solid backlight. Each pixel on an OLED screen is an “organic light emitting diode” that produces its own light. When the pixel is black, it isn’t producing any light. When the pixel is white, it’s producing light.
In other words, if you use a black background on an AMOLED display, your display will produce less light. This will help save battery power, squeezing more battery life out of your device.