How to dim non-jailbroken iPhone below dimmest factory setting?
If you find the minimum brightness still too bright for night-time reading, Apple has finally added a screen filter in iOS 8.  Typically Android offered a way to reduce the minimum brightness via apps when the screen was still too bright for nighttime reading even when set to zero but now you can enable this in iOS:


Go to Settings → General → Accessibility → Zoom.
Enable Zoom.
Triple-tap on the screen to bring up zoom options.
Choose filter: low light.
Go back to Settings → General → Accessibility → Zoom and change the zoom region to full screen.
Turn Zoom off.
Go to Settings → General → Accessibility → Accessibility Shortcut and set it to Zoom.


Now when you push your home button 3 times quickly it will dim the entire screen for night-time reading.