Patent Document ID: 4721389
Application ID: 06724774
Patent Status: 1

Claim One:
1. A method of measuring retroreflectivity of a reflective layer on a surface, comprising: illuminating a portion of said reflective layer with a laser beam of a predetermined wavelength emanating from a laser source while said portion is exposed to ambient light, said wavelength being in the range of from about 600 nm to about 650 nm and said laser beam being incident on said layer at a particular incidence angle (i), said incident beam being reflected in the direction generally back toward its source at least partially at a particular observation angle (o), said incidence angle and said observation angle being separated by a divergence angle (.delta.); filtering the laser light reflected at said observation angle through a narrow pass filter centered on said predetermined wavelength; picking up said filtered light with a photometer; and producing an electric signal corresponding to the amount of light incident on said photometer, said signal thus corresponding to the retroreflectivity of the illuminated portion of said reflective layer.