Coatings can be classified by either their appearance, such as glitter, or by their function, such as corrosion protection. However, pigments are currently being manufactured with new and unique appearance attributes that can not be characterized by traditional methods. These coatings may exhibit differences in their perceived color with changes in the illumination or viewing angle, or both. Properties such as these have become rudimentary in the production of currency, cosmetics, and retroreflective materials. The primary impetus of goniospectrometry at NIST is to develop accurate measurement protocols for reproduction and quality control of appearance attributes, such as color matching, by determining the minimum set of illumination and viewing geometries needed to accurately characterize the perceived color. Here, we present a new goniospectrometer developed at NIST that allows the measurement of the complete bi-directional reflectance distribution function (BRDF) for colored surfaces with the objective of differentiating between the scattering mechanisms in the coating. The illumination is provided by a monochromator with a spectral resolution of 0.05 nm between 360 nm and 780 nm. The sample can be moved about 3 different axes, allowing illumination and viewing for any direction within the hemisphere about the sample, including grazing angles, with accuracy better than 0.01 for each axis. This equipment will become the future provider of standard BRDF measurements at NIST, for the characterization of complex surfaces like gonioapparent coatings or retroflective surfaces.
Conference Dates: July 31-August 4, 2005
Conference Title: Optics and Photonics Symposium
Pub Type: Conferences
BRDF, color, color measurement, gonio-appearance, goniospectrometer