The Cass Creek Harmon's FireTacks Trail Marker utilizes retro-reflective technology to give you a guaranteed way to get into and out of the woods in low light conditions. The Cass Creek Harmon's FireTacks Trail Markers maintain reflectively in moisture conditions like rain, fog, sleet, or snow - conditions where ordinary trail markers virtually disappear! "Retro-reflective" means, that these markers have the highest visibility when your flashlight is aimed at them at eye level. To use Cass Creek Harmon's FireTacks Trail Reflectors, place tacks on trees at desired height (any level will work). Because Cass Creek Harmon's FireTacks are so incredibly bright, you will need fewer tacks per distance. If you hold your flashlight at your side, FireTacks may appear dim or even invisible. When you move your flashlight near your eyes for viewing, Cass Creek Harmon's FireTacks Trail Light Reflector Markers will "pop" out and be brighter than anything you have ever seen!