Nonspecular

Nonspecular refers to a characteristic of light reflection or scattering that deviates from the ideal specular reflection. In specular reflection, incoming light rays are reflected at an equal and opposite angle to the angle of incidence, resulting in a clear, mirror-like image. This occurs on smooth surfaces.

Nonspecular reflection, on contrast, happens on surfaces that are not perfectly smooth at the scale of the wavelength of light. These surfaces are often described as rough or textured. When light strikes a nonspecular surface, the individual rays are reflected in many different directions, rather than in a single, predictable direction. This diffuse scattering prevents the formation of a sharp, coherent image. Instead, the reflected light appears spread out.

Examples of nonspecular reflection can be observed when light bounces off matte paint, paper, or the surface of a cloud. These surfaces scatter light in all directions, making them appear bright but not reflective in the way a mirror is. The degree of nonspecularity depends on the texture of the surface relative to the wavelength of the incident light. A surface that appears smooth to the human eye might still exhibit nonspecular scattering for shorter wavelengths of light, such as ultraviolet or X-rays. This phenomenon is fundamental to understanding how we perceive the appearance of most objects in our environment.