In fact, if light of a particular electric vector orientation (plane polarized light) impinges on a sample, only those molecules which are properly oriented relative to this electric vector can absorb the light.
Specifically, the probability of the absorption is proportional to the cosine squared of the angle q between the exciting light and the transition dipole (cos2 q).
Hence, when we excite an ensemble of randomly oriented fluorophores with plane-polarized light we are performing a photoselection process, creating a population of excited molecules which nominally have their excited dipoles lines up with the polarization direction of the excitation.  This process is illustrated below:
hn
Potential dipoles
Excited state dipoles
q
Dipole II