Abstract
A photometer has been developed which is the first portable testing instrument whose measurements correlate completely with full-scale laboratory data and actual highway conditions. It provides accurate measurement of performances at discrete viewing angles throughout the range of modern reflector usage. The basic components of the photometer are (1) a light source to illuminate the reflector, (2) a photoelectric receiver to measure the intensity of the reflected beam at discrete observation angles and converts these measurements to specific intensity values which are indicated on a galvanometer, and (3) a goniometer on which the test reflector is mounted.