Alright math time.

A quick google comes up with this blog post, which I haven’t vetted or even read at all, it just has a table with some stats dodonut.com/blog/does-dark-mode-save-battery/

Apparently going to dark mode with 100% brightness provide a net saving of 40% on a pixel 2. Let’s assume this is universally true for all OLED and AMOLED displays, LCD users won’t see a difference, neither will CRTs but … I don’t think that I’ve heard of a CRT display on a phone.

40%? That sounds like a lot, doesn’t it?

Well yes and no, in relative terms it’s impressive, but it really depends on absolute terms. So how much does a phone use? The pixel 2 from before comes with a 10.39Wh battery, let’s assume you’re average use is 80% per day, then that comes out to 8.32Wh per day per phone. That means that the 40% reduction is 3.33Wh.

Is that a lot? Depends, if your only power source is a potato with a bit of copper and a galvanized nail, then yes, otherwise no.

Over the course of a year 3.33Wh a day comes to 1.215kWh annually.

Let’s put that into some context. The largest Vestas offshore wind turbine is the 15MW V236 www.vestas.com/en/products/offshore/V236-15MW. It can produce 80GWh annually. With the saving of 1.215kWh per phone, then for every approx 66 million OLED phones, we can skip erecting one offshore wind turbine.

LCD users won’t see a difference, neither will CRTs

Dark mode does save power with CRTs. They shoot an electron beam into phosphors in order to display stuff on the screen - having a mostly dark screen means fewer phosphors need to be excited.