The optical properties of thin planar arrays of molecules of thickness up to a few molecular layers are examined using a point dipole representation for a molecule in an electric field, and calculating the optical constants using the electrostatic approximation. The effects on the macroscopic or empirical optical constants arising from : 1) fluctuation in number density and molecular orientation ; 2) dipole imaging in the substrate (treated as isotropic) ; 3) the number of molecular layers in the film, are examined. It is found that fluctuations generally introduce only second order effects, while imaging and number of layers can under certain conditions have pronounced effects, requiring that in general the effective optical constants be a function of substrate dielectric constant and the number of layers