Diffuse reflectance

Diffuse reflectance is light returned from a surface or material after scattering redirects it into directions other than the specular reflection direction. Its measured value depends on wavelength, illumination and collection geometry, and the material’s absorption and scattering.

Diffuse reflection: Reflection in which light is scattered into many directions rather than concentrated at the specular angle. It describes the directional redistribution that produces diffuse reflectance.
Diffuse reflectance spectroscopy: A spectroscopic method that analyzes light diffusely reflected from a sample. It uses wavelength-dependent reflectance to study absorbing solids and powders.
Reflectance: The fraction of incident radiant power reflected by a surface or material under specified conditions. Diffuse reflectance is one directional component of this broader optical quantity.
Bidirectional reflectance factor: A ratio comparing a sample’s reflected radiance in a given direction with that of an ideal diffuse reference. It is a geometry-specific quantity, not simply the total diffuse fraction.
Kubelka–Munk theory: A two-flux model of light absorption and scattering in a diffusely illuminated layer. It converts reflectance from an optically thick layer into an absorption-to-scattering ratio.
Diffuse reflectance infrared Fourier transform spectroscopy: An infrared spectroscopy method that collects diffusely scattered radiation from powdered or rough samples. It applies diffuse-reflectance measurement to infrared absorption without requiring transparent specimens.
Absorption coefficient: A measure of how rapidly a material attenuates radiation through absorption per unit distance. Absorption removes photons that might otherwise return from the sample.
Gloss: The visual impression of a surface’s specular reflection, commonly assessed at defined angles. Gloss tracks concentrated reflection that diffuse-reflectance measurements may exclude or suppress.
Radiative transfer equation: An equation describing how radiation changes through absorption, emission, and scattering in a medium. It provides a more general account of the transport processes simplified by Kubelka–Munk theory.
Integrating sphere: A hollow spherical optical device whose reflective interior distributes collected light across its surface. It collects light over many directions to measure diffuse reflectance.

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Kubelka–Munk equationRelated: The equation uses diffuse reflectance as its observable input.