Transparency: Air inclusions or flaws may occur during the manufacturing process and can affect the beads ability to reflect light back to its source (also called retro reflectivity). The more transparent or clear a glass beads is, the better light can pass in and back out of it.
Roundness: Roundness also affects the beads ability to reflect. In order to be retro reflective beads must be round so that they can reflect light back toward the light source. As a rule the more transparent and rounder the glass bead is the better it reflects. However, a “cleaner”, rounder bead is also more expensive to manufacture which increases the cost to the consumer.
Size: Bead size is typically expressed in terms of U.S. sieve number, or the size of mesh screen that a bead will pass through. A mix of sizes increases the possible coverage and guarantees a wide range of reflection angles. For example, a topical application of reflective glass beads on painted interstate lines will utilize a variety of sizes ranging from 20 to 325 US Mesh. A topical application on airport painted lines requires a rounder, clearer, slightly larger bead. These are applied so that the refraction index and the reflection angles are more consistent. In street signs and some reflective tapes 100-200 US Mesh or smaller are used.
The glass bead’s Refractive Index is another important factor.
So, what is the Refractive index? It is actually very simple. Refraction is the bending of the light. When light enters a glass bead it is refracted and reflected. The glass beads’ ability to bend light is measured by its index of refraction. The higher the refractive index of the bead the better it reflects. Most beads used on traffic paint (highways and interstates) commonly have a refractive index of 1.5.
Here are a few:
• Reflective glass beads are used to make signs, tapes and reflective fabrics. See www.colesafety.com
• Reflective glass beads can even be used to make projector screens!
• Reflective Vinyl letters using micro reflective glass bead technology can be used to make banners and signs even more noticeable and visible especially at night. See www.colesafety.com