According to an embodiment there is provided a bi-directional reflectance distribution function (BRDF) instrument, including an enclosure having a plurality of sides. A first side has a relatively high reflectivity substantially non-specular interior surface, while each of the remaining sides has a relatively low reflectivity interior surface. A bottom of the enclosure has a relatively low reflectivity interior surface. A viewport is formed in one of the plurality of sides or the bottom, at least one exit port is formed in at least one of the sides, and at least one entrance port is formed in at least of the sides.