Both the Google Pixel 4 and Pixel 4 XL utilize displays with a 90Hz refresh rate. That's a good thing, but that refresh rate is not active all the time. In fact, if your brightness goes below a specific level, the phone reverts back to 60Hz (confirmed via ADB and logcat).
This is quite surprising, and one might say controversial even. When you navigate to display settings on the Pixel 4, and tap on the 'Smooth Display' option, you'll see a toggle for the 90Hz refresh rate.
If that 'Smooth Display' setting is on, the phone ends up utilizing the 90Hz refresh rate. Google states, in that menu, that it will raise the refresh rate from 60 to 90Hz 'for some content'. It also notes that this increases battery usage.
Now, some of you may presume that the 90Hz refresh rate will activate for all apps that allow for high refresh rates. That would mean a lot of apps, as very few popular apps do not have support for the 90Hz refresh rate.
Google Pixel 4 will use 90Hz refresh rate only if your brightness level is over 75%
Well, that is not the case, it seems. The Pixel 4 and Pixel 4 XL will utilize 90Hz refresh rate only if your brightness is at 75-percent or higher.
If you own a Pixel 4 or Pixel 4 XL, you can test this for yourself. Navigate to a website like testufo.com, which tests browser refresh rate. Increase the brightness and try it out, then do the opposite.
There are a few exceptions, though. If you have Ambient EQ enabled, the 90Hz refresh rate will remain active at a lower brightness setting. That will happen only if you are in a bright environment, though.
Also, if you go into Developer Options, and force 90Hz refresh rate on either Pixel 4 unit, you won't have issues at all. Toggling that 'force' switch in Developer Options will basically keep the phone at 90Hz at all times.
It's quite noticeable when the phone reverts back to 60Hz
It is quite noticeable when it drops to 60Hz, as the content becomes choppy. You may have never noticed that at 60Hz displays, but when you use a 90Hz display for a bit, it becomes extremely noticeable.
Google probably did this in order to save battery life, but what good is a 90Hz display if you can't use it. Just because your brightness is below 75-percent, doesn't mean your refresh rate should be lower as well.
Many people prefer lower brightness settings on their phones. Why use high brightness if you're indoors, or at night. It would make sense for the refresh rate to decrease if such choppiness becomes less obvious with lower brightness, but that's not the case at all.
Google should have just included larger batteries in both the Pixel 4 and Pixel 4 XL, and be done with it. This is really not a solution.