text: The interpretation of scattering measurements made at the multiangular locations relies upon some knowledge of the a priori properties of the particles or molecules measured. The scattering characteristics of different classes of such scatterers may be interpreted best by application of an appropriate theory. For example, the following theories are most often applied.
  Rayleigh scattering is the simplest and describes elastic scattering of light or other electromagnetic radiation by objects much smaller than the incident wavelength. This type of scattering is responsible for the blue color of the sky during the day and is inversely proportional to the fourth power of wavelength.
  The Rayleigh–Gans approximation is a means of interpreting MALS measurements with the assumption that the scattering particles have a refractive index, n, very close to the refractive index of the surrounding medium, n. If we set m = n/n and assume that , then such particles may be considered as composed of very small elements, each of which may be represented as a Rayleigh-scattering particle. Thus each small element of the larger particle is assumed to scatter independently of any other.
  Lorenz–Mie theory is used to interpret the scattering of light by homogeneous spherical particles. The Rayleigh–Gans approximation and the Lorenz–Mie theory produce identical results for homogeneous spheres in the limit as .
  Lorenz–Mie theory may be generalized to spherically symmetric particles per reference.
  More general shapes and structures have been treated by Erma.
  Scattering data is usually represented in terms of the so-called excess Rayleigh ratio defined as the Rayleigh ratio of the solution or single particle event from which is subtracted the Rayleigh ratio of the carrier fluid itself and other background contributions, if any. The Rayleigh Ratio measured at a detector lying at an angle θ and subtending a solid angle ΔΩ is defined as the intensity of light per unit solid angle per unit incident intensity, I, per unit illuminated scattering volume ΔV. The scattering volume ΔV from which scattered light reaches the detector is determined by the detectors field of view generally restricted by apertures, lenses and stops. Consider now a MALS measurement made in a plane from a suspension of N identical particles/molecules per ml illuminated by a fine beam of light produced by a laser. Assuming that the light is polarized perpendicular to the plane of the detectors. The scattered light intensity measured by the detector at angle θ' in excess of that scattered by the suspending fluid would be
  where i(θ) is the scattering function of a single particle, k = 2πn/λ, n is the refractive index of the suspending fluid, and λ is the vacuum wavelength of the incident light. The excess Rayleigh ratio, R(θ), is then given by
  Even for a simple homogeneous sphere of radius a whose refractive index, n, is very nearly the same as the refractive index "n" of the suspending fluid, i.e. Rayleigh–Gans approximation, the scattering function in the scattering plane is the relatively complex quantity
  :,   where
  and λ is the wavelength of the incident light in vacuum.