Measuring the performance of a solar cell is a tricky affair, and even more so for new technologies such as perovskites and tandem cells. In the laboratory, these are measured over a period of several minutes to ensure accurate characterization. But as technology continues its journey toward commercial production, ensuring an accurate power rating without slowing down the manufacturing process presents a new challenge both for suppliers of flash testing equipment and those working on bringing perovskite solar cells and tandem devices featuring them to market.