Both prism and glass bead reflective tape options are available because both methods of reflecting light have ideal characteristics depending on the intended use. The intended viewing distance is the primary factor in choosing the best option for your application.
Glass bead reflective tape is more affordable, less reflective and reflects light back at a wider angle. In shorter distance this reflective type is visible to more angles and a greater area of the tape is “lit up” by the light source. The results are more of a “flood light” effect which is great at close distances. Glass bead reflected light dissipates over distance and loses the intense glow after a few hundred feet.
Prism reflective tapePrism reflected light can be seen at great distance and are designed to be noticed at a quarter to half of a mile away.
High intensity reflective tapes compared over distance:
Prismatic reflective tape returns light in a close, parallel pattern. Glass bead reflective tape will disperse the returned light in a wider angle. This effect is helpful in close distance viewing situations and may make the bead reflective tape more easily viewed by a greater number of viewpoints. An example would be a construction worker wearing glass bead retro-reflective stripes on a hard hat. When he is illuminated by work lights aimed in his direction, the reflective stripes on his hard hat will light up for those standing in front of the light as well as other people in the range of the reflected light disbursement. Also, as the worker approaches the beam of light, the reflective stripes will begin to light up even before they are in the direct path of light. For this reason, the high intensity glass bead tape may be the best option for close up applications. When choosing reflective tape to be viewed at greater distances, the prism technology reflective tape is a better option. At about 500 feet, the light reflected from glass bead tapes will begin to disappear and at a distance of 300-400 yards it will not be useful. On the other hand, prismatic tape is still visible over a half mile away.
Glass Bead Reflective Tapes
Retroreflective tape using glass bead technology contain a layer of microscopic glass spheres. Light enters the sphere and is reflected back to the light source. Variations in the glass bead shapes and coatings cause some reflected light to reflect in different angles and only some light is reflected back in a truly retroreflective direction. About 30% efficiency is normal.
Refraction of light:
Light striking the glass bead is refracted and reflected. Refraction is the bending of light similar to the illusion of a bending pencil when it is dipped into a glass of water. This ability to bend light is called the index of refraction when comparing reflective beads. This index compares the ratio of the sine of the angle of incidence to that of the refraction. Various chemical and physical characteristics of the glass beads will determine the amount of light retroreflected.
How beads retroreflect light:
A reflective surface will reflect or bounce light off, within limits of reflective angles, retroreflective surfaces will redirect the reflected light back toward the light source. Here is a brief explanation of how glass beads achieve retroreflectivity. As the light enters the bead it is bent and refracted downward. This beam then shines on the back surface of the bead which is on top of a coating layer, creating a mirror like effect. The light reflected off the coating reflects and is refracted back toward the viewer. The resulting bright reflection back toward the light source is called retro-reflection. This is ideal for highlighting things that would normally be lit up from the vantage point of the person viewing the object. Headlights, flashlight and back up lights are all examples of personal light source that would be reflected back toward the eyes of the viewer.
Glass bead reflective tape comparison:
The two most common types of glass bead reflective tape is classified as type 1 and type 3. Type 1 is commonly referred to as a standard grade or engineer grade reflective tape. White engineer grade tape reflects at about 75 candlepower. Other colors will reflect at lower levels depending on the color. Type 1 reflective tape is very popular and is used for general applications, road signs, gate highlights, vehicle safety striping and equipment marking. Type 3 reflective tape is for high intensity applications. Type 3 tape uses a honeycomb pattern to group high index beads and return a much higher light value to the viewer. Reflected light from high intensity white tape returns 250 candlepower. Road construction barrels and traffic cones use Type 3 reflective high intensity tape.
Prismatic Reflective Tape
Prism technology high intensity reflective tape returns and impressive 80% of light back to the light source. Using a much more precise design, this method of reflection is much brighter than glass bead tapes. Prism type reflective tape reflects light through a system of precision flat mirrors that increase efficiency and eliminate the curved refraction disbursion of glass beads. By reflecting a concentrated beam from precise angles, the reflected light can travel much further distance before being dispersed. When long distance applications of ~1/4 mile are required such as the Conspicuity DOT regulated reflective truck tape or coast guard search and rescue SOLAS tape, a prismatic tape is required. Prismatic tape classification starts with a Type 4 up to a Type 9. All the listed high intensity prism tape options are so bright the human eye may not notice the difference in the various prismatic types. Only when viewed at a great distance are you able to distinguish the difference. The greater the distance for the intended application the higher the type rating required. With a candlepower reflection value requirement of 900, the SOLAS coast guard approved tape is extremely bright for spotting life jackets or life boats at sea. This level of reflectivity may seem high but it is a vital tool for search and rescue operations when spotting the reflective glow a thousand yards away.
Common uses of prismatic reflective tapes are DOT C2 Tape, FRA Railcar Tape, SOLAS coast guard tape, School Bus Tape, Chevron Reflective Striping, and Sign Sheeting.