We have long known that applications with dark mode / night mode can extend battery life on smartphones with OLED displays. It's true on Android and it's true with iPhone. This is because the individual pixels should do less work on dark areas of the screen, and they use almost no juice at all when they show true blackness. As SlashGear picked up, Google repeated this during its Android Dev Summit this week, showing more slides comparing power features of several different colors. (The company used its original Pixel smartphone for these data points.)
You can see that white removed uses the most effective. This led to Google recognizing that the appearance of white across its own apps and Android's style guidelines is good, less than ideal. It is everywhere, and it does not change with Google's renewed material design.
Fortunately, the company seems to recognize the value of dark state. YouTube and Android messages already have it, and Google also brings the feature to its phone app and tests it in the mobile Google Feed. Android can also be set to a dark theme for the fast settings pulldown and app drawer, but Google has not yet gone so far as adding a system-wide nightstand. (That's something Samsung plans to do with its new One UI.)
As an example of the dark state that comes to battery rescue, just look at the big difference below where Pixel is set to 100 percent brightness. The energy savings in the dark state are clear. I usually stick to the traditional look of these apps as I find white text on black a bit hard on my eyes, but it's nice to see that Google recognizes the value of relieving the white one. Make it a choice where it makes sense.