Street signs, work zone signs, fire escapes and any number of other signs are all useless if they're invisible after sunset. For drivers, joggers or anyone else traveling after dusk or before sunrise, the ability to see a warning sign can be all that's necessary for accident prevention. It might not be feasible to mass produce signs that glow in the dark, but reflective signs provide the necessary visibility in low light situations.
Sign reflectivity isn't just a good idea – in some situations, it's a requirement. Depending on the circumstances, different signs may require higher or lower levels of reflectivity. The Manual on Uniform Traffic Control Devices (MUTCD) goes into great detail on the specifics of when and where different types of sign reflectivity are necessary. This article will discuss the differences between those categories and the advantages and drawbacks of each.
The categories of reflection
In discussing sign reflectivity, it's important to distinguish between specular reflection, diffuse reflection and retroreflection. According to RoadVista, spectral reflection is when light bounces off a surface at an angle, like what happens when you shine a light on a mirror. Diffuse reflection is when the light source bounces off a surface in many directions – as when the reflector has an uneven surface. Retroflection is the category that applies best in signage because retroreflectors return light to the source, regardless of the angle. There are ten specific types of retroreflection, but No. 4 through 10 are similar enough to be listed under one subheading, according to TrafficSign.us:
- Type I: Engineer grade reflectors are composed of small glass beads encased in a translucent sheet. It's highly durable and should last about seven years, but doesn't provide the same level of retroreflection as other types.
- Type II: Super engineer grade reflectors operate in the same way as Type I, but they use larger glass beads for greater reflectivity. This sheeting has a 10-year service life, but they also cost more.
- Type III: High intensity sheeting or "encapsulated lens" consists of two layers. On the outside, a translucent pigmented sheet, and on the inside, a reflective layer of glass beads. A honeycomb lattice connects the two layers. Type III is the minimum recommended reflectivity level by some agencies, like the Arizona Department of Transportation.
- Type IV-X: The final seven types can be lumped into a single category, called microprismatic sheeting. Instead of glass beads, the reflective layer relies on microscopic cube-corner reflectors. Type IV sheeting is about seven times brighter than Type I and has a similar cost to Type III, along with a 10-year life. The other types differ in small ways, such as the use of a flexible, vinyl-backed sheeting in Type VI, useful for roll-up signs and clothing.
Retroreflective signs tend to fail in different ways. Types I and II may lose their reflectivity over time, usually due to overexposure from UV rays. Type III and other multi-layer sheetings tend to fail structurally, as the outer layer degrades and peels off. But by purchasing high-quality signs protected by SignMuscle™, organizations can ensure their signs' reflectivity remains intact over a longer period of time.