Rapid progress in organometallic vapor phase epitaxy of III-phosphide and III-nitride compounds in the 1990's paved the way for the development of advanced visible-spectrum light emitting structures based on AlGaInP and InGaN active layers, respectively. These material platforms have been introduced into novel, high power, device architectures for dramatic improvements in total light generation and extraction efficiency, resulting in solid state light sources with external quantum efficiencies in the range of 30-50%. In particular, advances in the III-nitride blue and near-ultraviolet devices have enabled the efficient generation of white light through excitation of down-converting phosphors such as YAG:Ce. High power white LEDs are now commercially available with luminous efficiencies of 30-40 lm/W, exceeding that of standard incandescent (~17 lm/W) and halogen (~25 lm/W) bulbs. In addition, new classes of phosphors are being developed to further improve the emission spectral content, and thus color rendering quality, of white LEDs towards applications in indoor and retail illumination. The current state of the art for such solid state light sources will be reviewed, along with an outlook towards future applications and performance.