Why are FireTacks so bright? The short answer is that they are retroreflective. Retroreflective means that much of the light shown at an object will be reflected back to the source. You most frequently see this effect on road signs. These signs are designed to be visible from distances sufficient for the sign to be helpful. Stops signs you can’t see until it’s too late are not helpful.
In every day circumstances most objects we see are either diffuse reflective of mirror reflective.
In mirror reflective materials the light is often directed away from the viewer. In this way these materials do not always appear bright to person holding the light source. The same cannot be said for the person viewing the reflection! Shiny or mirror like objects may seem like a good choice for building a night cache but generally they are not. There are more useful for creating effects that would make an night cache interesting but they do not work well as trail markers.
Diffuse reflection is what you get from something like snow or a white sheet of paper. The return path of the light source is spread out in many directions. In this situations the object will appear bright from a variety of angles but not much light is sent back to the viewer. We percieve these objects as being brighter than their surroundings but they aren’t necessarily very bright at all. These kinds of materials are best suited for increasing contrast between objects during the day. Increased contrast is helpful at night if you are trying to make it easier for the cacher to distinguish writing or shapes that make up part of your night cache.
Retroreflective materials in contrast can return as much as 58% of the light to the original source.This is why retroreflective materials are visible from great distances. There is one draw back to retroreflective materials and that is that they have a very small effective observation angle. This is the angle between the light source and your eyes. Typically for the observer to notice the retroreflected light their observation angle must be less than 1°. In most cases an observation angle over 2° renders the FireTack ineffective. FireTacks are effective when holding your flashlight slightly above your your head or no more than six inches below your eys. Make it easier on yourself and use a headlamps when following FireTacks. The retroreflective nature of FireTacks make them the best choice for trail markers. (Remember to use them for the trail out as well as the trail in, use different colors to distinguish the inbound and outbound trails.)
Flat trail markers are visible to the observer from head on or slightly to the side, around 60° either side of head on. By making FireTacks three dimensional there are more surfaces thus increasing the available viewing angles. As a result the observer has a better chance of seeing the trail.
The type of material used in the reflective trail marker also influences its brightness. FireTack brand trail markers use ASTM type VI and above materials while other brands use ASTM type II materials. The material used in FireTacks has 1000 prisms or glass beads impregnated in the material per sq. inch. The material material used in FireTacks is highly flexible, withstands impact, severe hot and cold, is guaranteed to maintain up to 75% reflectivity for ten years or more, even when left outside for the whole ten years.