Last night I laquered myself in bug spray and went out to Rockwoods Range Conservation Area for some practice at night orienteering. We're competing in a 24 hour adventure race next month, so our dauntless team captain Lisa (whom we borrowed from team Sisu) thought it would be a good idea to get some nighttime work in. I'm fairly comfortable orienteering during the day, but this was my first night attempt.
One interesting experience was the momentary blindness that occurs when you look up from your map to survey the surround. After staring at the white map with a bright headlamp you are momentarily "blind" when you look into the dark woods.
The temporary blindness occurs because it takes time for your eyes to fully dark-adapt and for you to regain your night vision. In short, this phenomenon is due a transitioning between the different types of photoreceptor in your eye: the rods and the cones.
The commonly said remedy is to use a dim red light, which has a wavelength that mutes this transition. That's what I remember from my neuro classes anyway. However, I found some debate about the value of the red light advice. So I'm going to have to do a little more book research and then a few "in situ" experiments on our next practice run.
The 1400 acre Rockwoods Range is home to one of the only permanent orienteering courses in the St. Louis area. You can get a map of the Rockwoods course from the St. Louis Orienteering Club for a few bucks.