Originally Posted by
slowpacer
I recently discovered a cycling app called "Jepster", it has built in feature for low power consumption, which basically makes the screen black with white letters, which in turn consumes less battery juice and makes the screen more readable. You can carry a USB power bank on your bike (top tube bag?) and keep your phone hooked up during your rides.
This may not have the intended effect.
Most phone screens today use LCDs. LCDs act as shutters in front of a backlight. The backlight will be on at the same intensity whether the screen is mostly dark or mostly light, and you can't realize any power savings from the LCD panel itself. Some LCD TVs have a feature called "local dimming" where the backlight is divided into multiple segments, which can be (you guessed it) individually dimmed. This is to improve contrast between lit-up and dark areas of the picture.. AFAICT, this is not used on phones, but in theory, if it were present, it might offer some power-saving benefit.
There are (or will be) some phone screens that use OLED or micro-LED screens. With these, because the light is emitted directly from the individual pixels rather than transmitted through them, there can be some power savings if you can turn most of them off.