NIST reference goniophotometer for specular gloss measurements

The measurement of specular gloss consists of comparing the luminous reflec tance from a test specimen to that from a gloss standard, under the same ge ometric conditions. The reference goniophotometer described here was design ed and characterized to comply with the geometric and; spectral conditions specified in the international documentary standards for specular glass mea surements at the standard: geometries of 20, 60, and 85 degrees In addition , this instrument measures the bi-directional luminous reflectance and tran smittance for incident angles from 0 to 85 degrees. The goniophotometer and the measurement procedures are described in this paper, as well as the cha racterization of the instrument and uncertainty analysis. The minimum relat ive expanded uncertainty (k=2) for the reference goniophotometer is 0.3%.