Retroreflection from spherical glass beads in highway pavement markings. 1: Specular reflection

The use of spherical glass beads in both vertical and horizontal highway markings to enhance nighttime visibility is common throughout the world. There has been, however, little theoretical analysis performed in order to optimize the various parameters for maximum retroreflection, especially for the case of horizontal reflectors. This paper presents a study of the retroreflection of spherical lenses used in horizontal pavement markings, concentrating initially on the specular contribution. The retroreflection characteristics are studied as a function of index of refraction and multiple specular internal reflection. It is shown that specular reflection does not contribute significantly to the total flux of retroreflected light reaching the motorist's eyes.