A series of iron garnet films of composition Lu3-xBixFe5-yGayO12 grown on (100) oriented GGG substrates have been studied using variable angle spectroscopic ellipsometry and polar Keff spectroscopy (MOKE). The diagonal and off-diagonal components of the permittivity tensor have been determined in the range 1-5 eV Our results seem to be in accordance with previously reported measurements on similar systems. We find that the optical absorption is reduced as the gallium content is increased. With increased Ga doping we also see an increase in the real part of epsilon(0) above 3.7 eV, but a decrease for lower energies. In the spectra of the off-diagonal permittivity tensor components we observe bismuth enhancement and gallium dilution effects. (C) 2003 Elsevier B.V. All rights reserved.