Many people in our modern world rarely if ever experience night vision. To achieve this interesting state of sensory awareness you cannot look at your cell phone or any other source of bright light for 30 to 45 minutes. Your night vision comes about over time because the rod sensors in the retina of your eye undergo a chemical change when they are placed in total darkness. The process starts immediately but takes 20 to 30 minutes to get 80% of maximum sensitivity. The night vision process can be reversed in seconds by exposure to a bright light. In it's most sensitive state your eye can function with a billion times less light than is present in strong sunlight enabling you to see a candle flame from 1.6 miles away.