Flavins are a family of ubiquitous redox cofactors which play a role in a variety of light-sensitive biological phenomena, including phototropism in plants and the perception of magnetic fields by migratory birds. I am interested in how the photophysics of flavins is affected by interactions with the local protein environment. There is evidence, for example, that some redox forms of flavins have radically different absorption and emission spectra in different micro-environments. An understanding of such behavior may be developed in a bottom-up approach starting from benchmark measurements of the transition energies of bare flavin molecules isolated in vacuo. These measurements utilize specialized techniques combining optical spectroscopy with mass spectrometry, which are known as action spectroscopy. I will present some of the first steps we have taken in this direction, with an emphasis on flavin adenine dinucleotide (FAD), the most common and most complex type of flavin.