We report the results of photoluminescence (PL), transmission and photoconductance (PC) studies of InxGa1-xN alloys grown by metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). First, we demonstrate that PC measurements allow to determine the gap energy and give the same value as transmission experiments in the case of thin InGaN layers. Second, we have performed PL and PC measurements in thin InGaN films. The comparison between the PL peak and PC measurements gives the Stokes shift. We study the Stokes shift as a function of temperature, and explained it in terms of localization and Burstein - Moss effect. Finally, we show that our measurements can be extended to the case of InGaN/GaN quantum dots. (C) 2001 Elsevier Science B.V. All rights reserved.