The FPbase spectra viewer enables the comparison of hundreds of FPs and organic dyes with thousands of filters, light sources, and detectors from many vendors. Shown here is a typical use case: the calculation of emission collection efficiency for multiple FP–emission filter pairs. Spectra are (optionally) shown scaled to excitation efficiency (here, a 561-nm laser), extinction coefficient, and quantum yield. Each table item shows the expected brightness (taking the extinction coefficient, quantum yield, and excitation efficiency into account) and the collection efficiency (the fraction of emission collected by the emission filter) for that FP–filter pair. Pressing the eye icon reveals the overlap integral for that FP–filter pair on the graph.