Abstract: A method and an apparatus for testing photovoltaic modules are provided, wherein power that a photovoltaic module outputs or draws is modulated a modulating frequency, the photovoltaic module is scanned using a camera and the camera signal generated by the camera is evaluated in order to obtain a luminescence image of the photovoltaic module which is used for detecting defects on the photovoltaic module. The photovoltaic module is operated only in the forward direction and the camera signal is evaluated using a digital filter, such as a lock-in filter.