NIST reference goniophotometer for specular gloss measurements

The measurement of specular gloss consists of comparing the luminous reflectance from a test specimen to that from a gloss standard, under the same geometric conditions. The reference goniophotometer described here was designed and characterized to comply with the geometric and spectral conditions specified in the international documentary standards for specular gloss measurements at the standard geometries of 20, 60, and 85°. In addition, this instrument measures the bi-directional luminous reflectance and transmittance for incident angles from 0 to 85°. The goniophotometer and the measurement procedures used to determine the specular gloss of nonmetallic samples are described in this paper, as well as the characterization of the instrument and uncertainty analysis. The minimum relative expanded uncertainty (k=2) for the reference goniophotometer is 0.3%. Optical Technology Div., Gaithersburg, MD 20899-8441.