In a nutshell: Dark mode is a common feature in many apps and operating systems these days, including iOS 13. While helping to prevent eye strain in low-light environments, it also saves on battery life—but by how much? A new test shows just how long an OLED-model iPhone will last when in dark mode compared to light mode.

The experiment was carried out by PhoneBuff over the weekend. Using two iPhone XS devices—one in light mode and one in dark mode—and some robotic arms, the test involved running identical tasks, including watching a YouTube video, navigating Google maps, using the Messages app, and scrolling through Twitter.

The results showed that iOS 13’s dark mode really does help extend the battery life of the iPhone XS. When the device in light mode died, the dark mode iPhone still had 30 percent battery. Check out the chart below to see a comparison between the phones.

The handsets were running at a fairly bright 200 nits so results will vary depending on your brightness settings, and the test only used apps that supported dark mode. But it still shows the difference dark mode can make.

It’s also important to note that with OLEDs, pixels are essentially switched off when showing the color black, whereas LCDs keep their pixels lit up no matter what is being shown on the screen. That means OELDs are always going to benefit more from dark mode.

Last year, Google showed off similar dark mode test results at its Android Dev Summit. They showed the difference in power usage between the original Pixel, which uses an OLED screen, and the LCD-sporting iPhone 7 in both normal and night modes. Google’s device draws 250mA while at maximum brightness in normal mode, while Apple’s phone was at 230mA. In Night Mode at max brightness, however, the Pixel’s draw drops 63 percent to 92mA, while the iPhone stays the same.