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Diffuse and specular reflection from a glossy surface. [1] The rays represent luminous intensity , which varies according to Lambert's cosine law for an ideal diffuse reflector. Diffuse reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than ...
Diffuse reflectance spectroscopy, or diffuse reflection spectroscopy, is a subset of absorption spectroscopy. It is sometimes called remission spectroscopy . Remission is the reflection or back-scattering of light by a material, while transmission is the passage of light through a material.
It is a diffuse emitter: measured per unit area perpendicular to the direction, the energy is radiated isotropically, independent of direction. Real materials emit energy at a fraction—called the emissivity—of black-body energy levels. By definition, a black body in thermal equilibrium has an emissivity ε = 1. A source with a lower ...
In optics, Lambert's cosine law says that the observed radiant intensity or luminous intensity from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal; I = I 0 cos θ.
A change in concentration over a distance is called a concentration gradient, a change in pressure over a distance is called a pressure gradient, and a change in temperature over a distance is called a temperature gradient. The word diffusion derives from the Latin word, diffundere, which means "to spread out".
(In contrast with Balfour Stewart's, Kirchhoff's definition of his absorption ratio did not refer in particular to a lamp-black surface as the source of the incident radiation.) Thus the ratio E(T, i) / a(T, i) of emitting power to absorptivity is a dimensioned quantity, with the dimensions of emitting power, because a(T, i) is dimensionless.
The apparent blue color of veins in skin is a common example where both spectral absorption and scattering play important and complex roles in the coloration. Light scattering can also create color without absorption, often shades of blue, as with the sky (Rayleigh scattering), the human blue iris, and the feathers of some birds (Prum et al. 1998).
Diffuse reflection of the incident light produced by the sample's rough surface reflection in all directions is collected by use of an ellipsoid or paraboloid mirror. Shape, compactness, refractive index , reflectivity and absorption of the particles are all characteristic of the material being analyzed.