Reddit users have
discovered that the Pixel 4's 90Hz refresh rate
drops to 60Hz when the display brightness falls below 75 percent. This means that you're only getting the full 90Hz display rate when the brightness level is high. The Verge reports:
It's not clear why Google has chosen the 75 percent mark, but droidlife has discovered you can head into the developer settings and force the 90Hz setting to always be enabled regardless of brightness levels. This will likely impact the battery life, which is something you'll want to consider before forcing the 90Hz display to always-on. Other 90Hz OLED Android phones like the OnePlus 7T keep the display running at its max 90Hz all of the time, but Google has stated it will automatically switch the display refresh rate on the Pixel 4 "for some content." Google issued a statement explaining its decision to limit the refresh rate, adding that it will issue an update in the coming weeks that will allow 90Hz in more brightness conditions.
Here's the full statement: "We designed Smooth Display so that users could enjoy the benefits of 90Hz for improved UI interactions and content consumption, while also preserving battery when higher refresh rates are not critical by lowering back down to 60Hz. In some conditions or situations, however, we set the refresh rate to 60Hz. Some of these situations include: when the user turns on battery saver, certain content such as video (as it's largely shot at 24 or 30fps), and even various brightness or ambient conditions. We constantly assess whether these parameters lead to the best overall user experience. We have previously planned updates that we'll roll out in the coming weeks that include enabling 90hz in more brightness conditions."
As for whether or not 90Hz has a serious impact on battery life, YouTube Tech Reviewer Matthew Moniz
reports only a marginal difference.