How to Block Light for Night Vision

The human eye takes up to 45 minutes to fully adapt to dark conditions and make the switch to scotopic vision, or "night vision." Once the eye is adapted, even an instant's exposure to light can reset the entire process of adjustment. When camping, stargazing or engaging in other nighttime activities outdoors, it is important to shield light sources so they do not interfere with the eye's gradual adaptation process.

Instructions

    • 1

      Switch off any nearby lights if possible, including yard lights and lights inside buildings. If neighbors or local businesses are contributing light pollution, consider asking them to turn off their lights after certain hours.

    • 2

      Install metal hoods on lights that cannot be turned off. This will reflect light downward and prevent excess glare. When buying new yard lights, choose covered fixtures that will direct light downward rather than radiating it into the sky.

    • 3

      Turn off cell phones, pagers, watch alarms and any other devices that may light up at unexpected times. Once your eyes have adjusted to night vision, you do not want to be surprised by a sudden illumination in your pocket.

    • 4

      Position yourself where tall trees or other obstacles block out any remaining light sources.

    • 5

      Choose a flashlight or headlamp with a red bulb if you need a light source for checking maps or charts. Red light provides the best spectrum for maintaining night vision, as the eye is less sensitive to longer wavelengths. Adapt any flashlight by wrapping the head with several layers of red cellophane, and securing with masking tape or a rubber band.