F. Perrin related the observed polarization to the excited state lifetime and the rotational diffusion of a fluorophore:  Perrin, F. 1926. Polarisation de la Lumiere de Fluorescence.  Vie Moyene des Molecules Fluorescentes. J. Physique. 7:390-401.
Specifically:
where V is the molar volume of the rotating unit, R is the universal gas constant, T the absolute temperature, h the viscosity and t the excited state lifetime. 
We can rewrite this equation as:
Where r is the Debye rotational relaxation time which is the time for a given orientation to rotate through an angle given by the arccos e-1 (68.42o). 
Polarization IV