Are you referring to the orientation factor kappa-squared in the Forster fluorescence resonance energy transfer theory? If so, this is rarely measured and is assumed to have the value 2/3. Here is a paper on the subject:

http://www.sciencedirect.com/science/article/pii/S0006349579852431

Yes Dr. Shapiro that is what I was referring to. I needed to make a few FRET calculations. Thank you so much for clearing the point.