If you're on Android, I recommend Screen Filter[1] which will draw a semi transparent overlay on top of nearly everything (depending on the phone and/or OS version, it might not dim the status bar, bottom navigation buttons, lock screen, etc.). I use it a lot when reading at night, because the lowest brightness setting on my phone is also too bright for dark-adapted eyes.

[1] https://play.google.com/store/apps/details?id=com.haxor