Dark mode can boost battery life but it hinges on the display tech you have.
There’s a lot of chatter about dark mode these days. Call it the latest fashion.
Google will add dark mode to Android Q and any app worth its salt is adopting it. And Apple has added a dark mode to iOS 13, due this fall. And the Mac already has it with macOS Mojave. As does Windows 10.
Dark mode and battery life: you want an OLED display
The tl;dr is you need an OLED display to get any battery-life benefit.
That’s because OLEDs actually turn off the pixels — i.e., they draw no power — in dark mode. That’s not the case for LCDs, which use power regardless of light or dark mode. This is spelled out in more detail by iFixit.
The obvious conclusion is, if you have a smartphone with an LCD (not uncommon*) or laptop or tablet with an LCD (almost universal), dark mode has no impact on battery life.
And note that dark mode has nothing to do with turning down the brightness on the display, which does affect (increase) battery life on devices with LCDs.
How much of an impact?
Tests on the iPhone (via AppleInsider) and Android (via a Google presentation courtesy of SlashGear) in dark mode and night mode, respectively, show that battery life on devices with OLEDs can increase dramatically in some cases.
The biggest impact could potentially be on laptops because large 13-inch and 15-inch displays are the single largest drain on battery-life. Laptops almost exclusively use LCDs but a few are starting to ship with OLEDs, including the just-released HP Spectre x360 15 and Dell XPS 15 7590.
*For example, while the iPhone X and XS have OLEDs, the iPhone XR has an LCD. And anything older than the iPhone X has an LCD. The Samsung Galaxy S series have OLEDs as do Google’s newest phones including the Pixel 3, Pixel 3 XL, Pixel 3a, and Pixel 3a XL.