In iOS devices, you can use the built-in accessibility settings to produce the dimmest, reddest screen possible in under a minute, absolutely free.
The process is identical on iPads and iPhones and is just as effective on both!
Follow these easy steps:
Settings > Accessibility > Accessibility Shortcut >
Enable Color Filters, Enable Reduce White Point.
Settings > Accessibility > Display & Text Size > Color Filters >
Enable, Set Intensity to maximum setting, Set Hue to minimum setting.
Triple-click Home button, disable Color Filters.
Settings > Accessibility > Display & Text Size > Reduce White Point >
Enable, Set slider to maximum setting.
Triple-click Home button, disable Reduce White Point.
Now, you can triple-click the Home button to instantly apply one or both settings. Reduce White Point is very strong when used in conjunction with the brightness slider; with both set to minimum, it can be difficult to read the screen even in complete darkness. I always set Reduce White Point before I go to bed, it makes your phone much easier on the eyes in the middle of the night and first thing in the morning.
Don't waste money on third-party solutions or tape red saran wrap to your screen if you have an iOS device!