Smartphones tout 'dark mode' as an energy-saving feature, because darker-colored pixels use less power than lighter-colored pixels.

It's mostly an intellectual placebo, finds a new study, because of the way most people use their phones on a daily basis. The study looked at six of the most-downloaded apps on Google Play: Google Maps, Google News, Google Phone, Google Calendar, YouTube and Calculator. The researchers analyzed how dark mode affects 60 seconds of activity within each of these apps on the Pixel 2, Moto Z3, Pixel 4 and Pixel 5.

Dark mode only made a noticeable difference to battery life in certain scenarios

Smartphones that came out after 2017 likely have an OLED (organic light-emitting diode) screen. Because this type of screen doesn’t have a backlight like the LCD (liquid crystal display) screens of older phones, the screen will draw less power when displaying dark-colored pixels. OLED displays also allow phone screens to be ultrathin, flexible and foldable.

But the brightness of OLED screens largely determines how much dark mode saves battery life and many people use their phone’s default auto-brightness setting, which tends to keep brightness levels around 30%-40% most of the time when indoors. At 30%-50% brightness, the researchers found that switching from light mode to dark mode saves only 3%-9% power on average for several different OLED smartphones.

This percentage is so small that most users wouldn’t notice the slightly longer battery life. 

Photo courtesy of Purdue University photo/John Underwood

Here they provide an example of switching from light mode to dark mode on a sunny day

Let’s say that you’re using your OLED phone in light mode while sitting outside watching a baseball game on a bright and sunny day. If your phone is set to automatically adjust brightness levels, then the screen has probably become really bright, which drains battery life.

The Purdue study found that switching from light mode to dark mode at 100% brightness saves an average of 39%-47% battery power. So turning on dark mode while your phone’s screen is that bright could allow your phone to last a lot longer than if you had stayed in light mode.

Other tests done by the industry haven’t analyzed as many apps or phones as Hu’s team did to determine the effects of dark mode on battery life – and they were using less accurate methods.

Scenario 2: Using dark mode to go easier on your eyes without draining your phone’s battery faster

Typically, increasing your phone’s brightness drains its battery faster – no matter if you are in light mode or dark mode. But since conducting this study, Dash has collected data indicating that lower brightness levels in light mode result in the same power draw as higher brightness levels in dark mode.

Using the Google News app in light mode at 20% brightness on the Pixel 5, for example, draws the same amount of power as when the phone is at 50% brightness in dark mode.

So if looking at your phone in dark mode is easier on your eyes, but you need the higher brightness to see better, you don’t have to worry about this brightness level taking more of a toll on your phone’s battery life.

Apps need to be developed to leverage dark mode for it to matter

The team built a tool that app developers can use to determine the energy savings of a certain activity in dark mode as they design an app. The tool, called a Per-Frame OLED Power Profiler (PFOP), is based on the more accurate OLED power model that the team developed. This could help because, for example, Android’s current “Battery” feature is oblivious to content on a screen, meaning it doesn’t consider the impact of dark mode on power consumption.

They developed a more accurate way to calculate battery consumption by the app for Android, and actually used the tool to make the study’s findings about how much power dark mode saves at certain brightness levels. Unlike Android’s current feature, this new tool takes into account the effects of dark mode on battery life.

The tool, called Android Battery+, is expected to become available to platform vendors and app developers in the coming year.