There are two kinds of reflectance, specular and diffuse. Specular reflectance refers to the part of the incident beam reflected at the same angle as the angle of incidence; mirrors typically produce specular reflectance when used as samples. Diffuse reflectance refers to the part of the incident beam reflected in all directions; powders produce diffuse reflectance when used as samples. Most samples produce a combination of specular and diffuse reflectance.