The science of reflective traffic signs is based on materials that allow signs to reflect back the light from drivers' headlights in order to improve readability. This technology has been around since the 1930s and has saved many lives, as it creates better visibility at night. Here's a deeper look at the science and evolution of reflective traffic signs.
Evolution of Reflective Signs
The history of reflective traffic signs began with inventor Harry Heltzer, who worked for 3M, which manufactures various types of adhesive materials for multiple industrial and commercial applications. He served as the corporation's Chairman and CEO from 1970 to 1975, after serving as VP since 1961. The reflective sign became one of 3M's most profitable products, according to the New York Times at the time of Heltzer's death in 2005.
Heltzer helped develop Scotch-Lite, which is the glass bead coating used on road signs and highway paints to project illumination. He is considered the "father of reflective materials." During his tenure at 3M, earnings rose sharply as the company expanded to serve over 150 countries.
In 1937 as a 3M laborer, Heltzer was assigned to make the center striping on Minneapolis highways more reflective at night. At the time white or yellow paint was the standard and did not provide enough reflectivity.
After a highway official suggested that he embed glass beads into the stripe, his mission was to create glass beads small enough to fit within striping. He used double-coated tape with beads on one side, although at first he couldn't figure out how to make it stick to Minnesota streets in the winter. Later he developed a glass-bead reflective compound that proved effective for highway striping. Heltzer ultimately earned six patents for reflective highway inventions.
Early retroreflective material was degraded by dirt. However, this issue was resolved with an economical enclosed lens system that has come to be known as engineering grade sheeting.
In the late 1960s the invention of encapsulated lens sheeting added a resin base and additional reflective coating. This development marked a much brighter and longer lasting effect than engineering grade sheeting. It's now the most widespread type of reflective material used for signage. In 1989 an even brighter and more durable but more expensive solution emerged that replaced glass beads with thousands of microscopic prismatic reflectors per square millimeter.
The reason aluminum is a popular choice for traffic signs is that it doesn't rust and can last many years. Steel coated with zinc is a more economical solution and has the same durable qualities. An even more affordable solution is a plywood blank covered with a layer of plastic, but this material does not last as long as metals.
Retroreflectivity vs Mirrors
Although it seems quite similar, retroreflectivity does not have the same effect as mirrors. With glass beads on or under transparent film, retroreflection allows a surface to return part of its light to the original source. While the sun scatters light in all directions allowing it to bounce off objects, mirrors cause light to bounce and reflect off surfaces at angles opposite of the sources. What makes retroreflective material different is that it allows light to bend and return directly toward the light source.
Retroreflective sheets are typically cut by hand, although a band saw is often used to cut multiple sheets. The sheets have adhesive backing making them easy to apply to a clean, dry surface.
Consider making your signs more illuminated at night with retroreflective sheeting. For more information about reflective traffic signs, contact Zumar at our Arizona, California or Washington location.