specular

Specular describes a type of reflection that is mirror-like, meaning light from a single incoming direction is reflected into a single outgoing direction. The term derives from Latin specularis, meaning pertaining to a mirror. In everyday use, specular can refer to surfaces that produce clear reflections and to the shiny quality of materials.

In optics, specular reflection occurs when a light ray hits a smooth surface and reflects with an angle of incidence equal to the angle of reflection. The surface roughness relative to the light’s wavelength determines how much of the light is reflected specularly. Very smooth surfaces yield strong, directional reflections, while rough surfaces cause diffuse scattering that spreads light in many directions. The Fresnel equations describe how reflectance depends on angle and polarization and explain why reflectivity can vary with viewing direction.

Specular should be distinguished from diffuse reflection, which arises from rough surfaces that scatter light uniformly and do not preserve the image of the light source. Many real surfaces are mixed, showing both specular highlights and diffuse color, with the balance dependent on material properties and lighting.

In computer graphics and rendering, the specular term models the shininess of a surface. Microfacet models treat a surface as a collection of tiny mirror-like facets whose orientations determine the size and intensity of the specular highlight. Parameters such as shininess or roughness control the sharpness of the highlight, while Fresnel effects modulate reflectance with viewing angle, aiding realism in digital images.

Specular reflection is fundamental in optics, photography, material science, and rendering, conveying gloss, shape, and surface quality through mirror-like reflections.