The size of a glass bead can affect retro-reflectivity, especially under wet conditions. Larger beads have slightly higher retro-reflectivity than standard beads under dry conditions.

Refractive Index

The higher the refractive index, the more light is reflected. Most beads used in roadway striping nationwide have a refractive index of 1.50.

Clarity and Roundness are the two essential properties that all beads must possess to retro-reflect light. The need for transparency and roundness can be explained by examining the path of light as it enters a bead embedded in a marking. The glass bead must be transparent so that light passes through the sphere. Clarity is strongly affected by the type of raw material used. Beads that are less than transparent block a portion of the light from entering.