Navigation in darkness and reduced visibility is a serious issue for the hiker. Important geographical and trail features (e.g., mountains, roads, forest, etc.) can be nearly impossible to see. This creates significant loss of geographic reference used during daytime travel. Geographic reference validates the hiker’s map.
Further compounding the nighttime challenge is the physiology of the eye. Our eyes are designed to provide optimal performance during periods of light. The components of the eye (the retina, rods and cones) are arranged specific to their function. The cones are the discriminators of fine detail and color. Cones are the most effective in light. In complete darkness, a cone’s effectiveness is significantly reduced. Rods are important to our nighttime vision.
What that translates to: In periods of extreme darkness, the ability to see with clarity straight ahead is significantly diminished. If you absolutely must continue traveling and navigating in darkness, the hiker should first make an effort to become adapted to the night environment. Avoid looking at any white light. Select a member of your group to follow behind you with the GPS and flashlight/headlamp, as its light will negatively impact your vision.
Red light is now best. Allow 15-30 minutes for the eyes to become adjusted; older hikers may need almost one hour. Continue to protect the now adapted eyes from sources of bright illumination. Discuss this with the other members of the group before embarking.
To maximize clarity, the lead hiker will need to scan the surroundings (by turning their head side to side) rather than looking directly at objects. This is where prior map study, commonly known as having a “mental map” will pay off significantly.
Navigation procedures are essentially the same as during daylight. Global Positioning Systems (GPS) lose no capability and will continue to direct hikers as before. Do note that the display screens backlight capability does not have red lighting, only white, and use will quickly degrade battery life. Always carry spare batteries.
Without a GPS, the navigator has the option of navigating by a process known as dead reckoning. Dead reckoning is navigation through the careful application of map and compass by evaluating azimuths and distance by pacing.
Navigation in darkness is challenging, potentially dangerous, and requires a high level of knowledge. Confidence from lots of practice performing these skills is essential. Practicing at night is strongly recommended before heading out to the wilderness.