Abstract The failure and loss analysis of solar cells relies on the precise determination of their electrical performance parameters. Light emitting diodes (LEDs) used as light sources in solar simulators provide a number of advantages compared to conventional Xenon-based solar simulators. In this work, we present an approach to rapidly measure the quantum efficiency and the reflectivity that takes the spectral broadening of the LEDs fully into account. Our approach does not rely on any specific shape of the spectral peaks and can thus be applied to any type of quasi-monochromatic light source. The two proposed methods yield valuable additional information on the solar cell performance and material properties that cannot be obtained by conventional solar simulators. Using LED solar simulators, they are completely in-line capable as they can be performed in less than one second.