Biological photoreceptors and fluorescent proteins provide striking examples of how non-covalent interactions could be exploited for tuning the photochemistry and photophysics of organic chromophores. In this tutorial review we show how the construction of computer models of such natural supramolecular systems not only provides atomic-level information on the mechanisms of their function, but also principles useful for designing light-responsive components of artificial supramolecular systems. Using a few complementary case studies, the intellectual process leading to the implementation of such an engineering target is followed up to the actual construction of a working prototype of a biomimetic molecular switch.