This exciting light will be absorbed by the fluorophore at the origin and give rise to fluorescence which is typically observed at 90o to the excitation direction, i.e., from along the Y axis.
We initially consider that this fluorescence can have any direction of polarization.  The actual direction of the electric vector of the emission can be determined by viewing the emission through a polarizer which can be oriented alternatively in the parallel or perpendicular direction relative to the Z axis or laboratory vertical direction. Polarization is then defined as a function of the observed parallel (III) and perpendicular intensities (I^) :
If the emission is completely polarized in the parallel direction, i.e., the electric vector of the exciting light is totally maintained, then:
Polarizers IV