What is the specular component of reflectance?

When light strikes a surface some of the light penetrates where it can then be absorbed, scattered, or even transmitted if the layer is sufficiently thin. Nevertheless, because of the change in refractive index between air and most substances, a certain proportion of the incident light is reflected directly from the surface. The angular distribution of this light depends upon the nature of the surface but light that is reflected at the opposite angle to the incident light is called specular reflectance. Light that is reflected by the substance itself is called body reflectance.

Sphere-based spectrophotometers often incorporate a so-called gloss trap which allows the specular component of the reflected light to be either included or excluded.