Xenon lamps have been the standard light source for the efficiency measurement since the beginning of industrial solar cell manufacturing.As a result of giant leaps in solid-state lighting technology,LED based light sources promise to be a better approach for various reasons.The main reason is the opportunity to combine various colors to match the suns spectrum more accurately.In the paper,we will discuss the strengths and weaknesses of Xenon and LEDs as well as the technical and economical implications.The pros (+) and cons (-) of Xenon based light sources are as follows: High power Parallel light Wide wavelength range Well established Large deviation from the norm spectrum,even with filters Short-term and long-term drift in spectrum Limited to short pulses Intensity dependence of spectrum Short life cycle of lamp The challenges for LED based light.sources are:a) Color diversity: The norm IEC 60904 is insufficient in terms of the mismatch factor.Using only few colors (e.g.,6 different sets of LEDs) allows full match with the norm but may still cause not negligible errors in current measurement.b) Color mixing: The colors need to be perfectly mixed to avoid a color pattern on the solar cell.c) For simple configurations the level of diffused light is high.The above issues will be addressed with experiments and PC-1D simulations in order to demonstrate their effect on accuracy and precision.