The Fraunhofer ISE calibration laboratory is internationally recognized for the characterization of multiple solar cells under one sun and concentrated light. For these measurements, it is essential that the current generation in each sub-cell corresponds to that below the standard AM1.5d spectrum. Today, for measurements under concentrated light, four flashlamps are ignited simultaneously with suitable filters. In order to be able to measure multiple solar cells with up to six sub-cells correctly, a new flash head with six lamps and six filters is being developed and thoroughly tested in order to be able to transfer it to calibration mode. Today no laboratory in the world is able to measure solar cells with 5 or 6 partial cells under concentrated light.