This work discusses the near edge photoluminescence and reflectivity of GaN layers grown on sapphire using three different methods. Particular emphasis is given to the importance of strain effects on intrinsic properties, as obtained from reflectivity, and that should be taken into account in the interpretation of luminescence spectra. High quality optical properties are obtained whatever the growth technique, halide vapor phase epitaxy (HVPE), gas source molecular beam epitaxy (GSMBE) and metal-organic vapor phase epitaxy (MOVPE), this last technique providing, at the present stage? the best results. (C) 1997 Elsevier Science S.A.