How to enable iPhone’s hidden ‘night vision’ mode that turns your screen red

The iPhone has a hidden "night vision" feature that turns your screen red. More than giving a spy movie vibe, a red screen could help sharpen people's night vision by reducing the harmful effect of the bright displays we stare at all day.

This is especially helpful at night and when we first wake up, since the regular light the iPhone displays can cause fatigue and harm our eyes. Apple already offers some built-in options to protect our eyes, such as:

• Warn that the iPhone is too close to your face
• Night Mode...