Retroreflective Glass Microspheres (Road Marking Grade)

The retroreflective efficiency of glass microspheres depends critically on refractive index. At RI ~1.9, the refracted light ray within the sphere exits at approximately 180° (directly back toward the light source) when the bead is partially embedded in the marking paint at the optimal depth (~40–60% of bead diameter above the paint surface). Standard soda-lime glass (RI ~1.5) produces significant divergence of reflected light, reducing retroreflectivity. RI 1.9–2.0 beads are the accepted standard for EN 1423 and AASHTO M247 compliant road marking retroreflective performance.