We report on the characteristics of blue superluminescent light emitting diodes based on the emission of InGaN quantum wells. Narrow ridge-waveguide devices realized by standard processing techniques and with extremely low facet reflectivity show single lateral mode emission and continuous-wave output powers >35mW with a typical spectral bandwidth of 4-5 nm. Tuning the composition of the active region, superluminescent light emitting diodes spanning all the spectral range between 410 and 445 nm could be realized. The light output is highly directional and results in a coupling efficiency into single mode fibers >50%. The device temperature behavior is also discussed. (C) 2010 The Japan Society of Applied Physics