A software package has been used to calculate and compare the photonic band structures for two structures: one structure consisting of dielectric cylinders in a square lattice, and the inverse; a structure with air columns in a dielectric matrix. The appearance of and differences between TE- and TM-gaps are compared. Transmittance for normal incidence was calculated for both structures, with a material thickness of 8 µm. The photonic band gap width at the X-point of the band structure as a function of the packing fraction of cylinders was investigated for the two cases.