Aarrghh! When we think of pirates, images of eye-patches come to mind. On an episode of Mythbusters, the team tested the hypothesis that pirates kept one eye covered so that it would remain sensitive in the dark, so that when they raided ships, they would uncover their patched eye below decks and have better vision in the dark. This proved to be true. It can take 10 to 20 minutes for your eyes to acclimate to the dark. It takes a moment of bright light to “blind” you until you can return to the dark and recover. In an emergency situation you may not have the needed time to recover your night vision.
A friend recently wrote to me about this principle that was taught to him by his grandfather. If you have been outside in the dark and need to go indoors briefly for some reason such as to answer a phone or fetch a tool, you can close one eye before entering the building and keep it close for the duration of your time inside. Once you exit, you can open your closed eye and it will retain it’s sensitivity in the dark. This technique could prove critical if you don’t have supplementary lighting like a flashlight.
Take time to practice this technique. Once you make the quick trip inside a lit area and then return to the dark, compare the vision from each eye and notice the difference.