text: If the particle in question is not spherical, the rotational motion must be considered as well because the scattering of the light will be different depending on orientation. According to Pecora, rotational Brownian motion will affect the scattering when a particle fulfills two conditions; they must be both optically and geometrically anisotropic. Rod-shaped molecules fulfill these requirements, so a rotational diffusion coefficient must be considered in addition to a translational diffusion coefficient. In its most succinct form, the equation appears as
  Where  is the ratio of the two relaxation modes (translational and rotational),  contains information about the axis perpendicular to the central axis of the particle, and  contains information about the axis parallel to the central axis.
  In 2007, Peter R. Lang and his team decided to use dynamic light scattering to determine the particle length and aspect ratio of short gold nanorods. They chose this method since it does not destroy the sample and it has a relatively easy setup. Both relaxation states were observed in VV geometry and the diffusion coefficients of both motions were used to calculate the aspect ratios of the gold nanoparticles.