Reflection from rough surfaces, such as asphalt, paper and clothing are examples of diffuse reflection. In diffuse reflection, light rays are scattered randomly at different angles from the reflecting surface.
Ideal diffuse reflection results in equal luminance in all directions at the half-plane adjacent to the surface. This ideal form of diffuse reflection is called Lambertian reflectance. Such ideal reflecting surfaces are hypothetical, and actual reflecting surfaces are anisotropic, reflecting more in certain directions than in others. Surfaces with a high degree of diffusive efficiency include plaster, paper, white marble and talcum powder.
Specular reflection is exhibited by a mirror or a calm water surface, where coherent incident light rays are coherently reflected according to the law of reflection. The incidence angle and the reflected angle are equal in perfectly specular reflection. All reflection obeys the law of reflection, but diffuse reflection results in scattering because the reflection angles from each part of the material are different due to the random orientation of the surface.
Even slight surface imperfections make perfect specular reflection impossible, so any reflection from a real surface will always be some combination of diffuse and specular. Diffuse reflection is used form ambient lighting applications, such as frosted glass bulbs, while specular reflection is used for optical applications, such as microscopes and telescopes.