According to a Purdue University Study dark mode can save 3 to 9% of your battery if you’re on auto brightness. Let’s say your average phone uses 15Wh per day (5.475 kWh per year). Let’s say 5 billion people use smartphones. That’s around 30 TWh for total yearly smartphone consumption.

So if everyone was using dark mode, it could save around 0.8 to 2.5 TWh a year in the best case scenario. But that is if everything on your phone was dark mode. Not sure how much time people spend browsing websites percentually.

That’s around 0.1 to 2.7 times the daily electric energy production of all nuclear power plants.

The world electricity production is around 23000 TWh per year, so you could save around 0.0036% to 0.01% of yearly energy consumption by switching everyone to dark mode.

Such impactful, much environment, wow

On devices with OLED screens, the more pixels on the screen are lit up, the more power the screen consumes. So on the majority of smart phones these days, dark mode will slightly reduce energy consumption. Devices with LCD screens will likely show no difference, and we’re talking a fairly negligible amount of power here anyway.