Enable Night-Reading Mode with iOS

To enable a dimmed “night” display mode for any application with an iOS device, tap the Settings icon and choose General –> Accessibility –> Triple-click Home and and set it to “Toggle White on Black.”

Press the Home button to exit Settings and launch any reading app.  Triple-click the Home button in quick succession and it should enable white-on-black effect.  Triple-click again to switch back to the default normal mode.  The main downside is that images (both within apps and on the web) will look like photographic negatives instead of normal photographs.