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With all due respect to ideath's more interesting writeup above, I would like to offer my advice on how to actually gain night vision in a pinch. Not suitable for when you're being chased by wild animals, but just fine for most camping trips or similar situations.
Materials:
- One candle
- Two eyes (Ha, ha. No, but this is important. This won't work if you only have one eye.)
The Procedure:
- First, we have to determine your dominant eye. Fix your view on a distant object, like a telephone pole or the top of a tent.
- Hold up your index finger and line it up with the object you chose.
- Close your left eye. Does your finger seem to move relative to the object? If so, your dominant eye is your left eye. If not, your right eye is in charge.
- Put your nondominant hand over your dominant eye. Close that eye.
- Light a candle. Keep your eye covered and closed! That's important! Maybe the candle should be fixed to a table.
- Stare fixatedly at the candle.
- Keep staring. Hold this position for 60 to 120 seconds. Don't peek.
- Open and uncover your dominant eye, but at the same time close and cover your weaker eye. This is important! It's cool to have both open, but if you don't do it properly you're toast. Never have both open at once.
- The world is now tinted purple, but you aren't done. Blow out the candle. Wait another 30 seconds or so, then open both eyes.
- Take a little time to let everything settle, and you now have night vision!
Cool, huh? Here's how it works. Your eye has a chemical, called rhodopsin. Staring at the candle is a low-tech way to trigger its release (physicsfordummies' writeup in night vision explains a more complicated way). The imbalance in chemical levels makes your eyes especially sensitive to light, and your pupils expand to allow more light to enter the eye.
Try it in the dark sometime, away from cities and light pollution.
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