Is there a fundamental difference between specular and diffuse reflection, or between diffuse reflection and scattering? I have heard various explanations that I am trying to sort out. (Please note that these "explanations" are not necessarily an accurate record of what was presented to me-- rather a reconstruction of what I understood them to mean. I am not a proper physics student, just an artist wanting to do my best to make sense of the interactions of light and matter.) Explanation #1 (what I initially picked up from art training): Diffuse reflection is the color of the object that we see when light bounces off a rough surface in random directions. Specular reflection (highlights) will be the color of the light source, and its angle of reflection is equal to the angle of incidence. The amount of specular reflection depends on surface smoothness. Sub-surface scattering occurs only in translucent material. Explanation #2 (after looking into it a bit more): The amount of specular reflection depends on index of refraction and not on surface polish. Light reflecting from the microfacets of a rough surface is still specular (though fuzzy) reflection of the light source. Diffuse reflection is actually a form of subsurface scattering and does not depend on the roughness of a surface but rather on the microtranslucency of the material. Even if they appear to be macroscopically opaque, all colored materials aside from metals have some amount of translucency. Light penetrates to some degree and is partially absorbed and reflected around within the material before re-emerging as colored. Scattering is simply a form of reflection in which the direction of the light seems to be random, but actually obeys the law of angle of incidence = reflection... it's just that the microfacet interfaces (either surface or within the structure of the material) tilt in so many unpredictable directions. Explanation #3 (after looking into--and probably grossly misunderstanding--quantum electrodynamics): Reflection is one possible average/aggregate of scattering probablilities. Scattering, compared to reflection, is a more fundamental interaction of light with matter-- the energy of light perturbs the electrons in the matter... if it is not a useful amount to jump energy states, it is quickly re-emitted in all directions, or at least having the probability of any direction. In certain circumstances, for reasons that I have failed so far to understand, the probabilities of certain paths cancel out and others add up, and it looks like reflection on a macro scale. Ok, so although quantum things do seem to be quite helpful to me in understanding why materials absorb certain wavelengths, with regard to the actions of light in general, I'm not sure that attempting QED really helps my already shaky understanding of classical/wave optics.... anyway, for now I would primarily like to know if I am on the right track with anything in Explanations 2 & 3, and what are the misconceptions that jump out? One thing that confuses me is that in Explanation #2, scattering seems to be a type of reflection; and in #3, reflection seems to be a type of scattering. I appreciate any thoughts-- thanks!