GaN is a defect-rich material with typical dislocation densities exceeding 108 cm−2. Light emission from InGaN layers grown on such GaN buffers used in blue and green LEDs is expected to be attenuated because of non-radiative recombination at such defects. Nevertheless, InGaN quantum wells, are efficient light emitters in green, blue, white and ultraviolet light-emitting diodes and diode lasers. The indium-rich regions have a lower bandgap than the surrounding material and create regions of reduced potential energy for charge carriers. Electron-hole pairs are trapped there and recombine with emission of light, instead of diffusing to crystal defects where the recombination is non-radiative. Also, self-consistent computer simulations have shown that radiative recombination is focused where regions are rich of indium.