Moerner’s demonstration of blinking and photo activation opened the road to exploring a vast space of GFP mutants for novel optical properties. J. Lippincott-Swartz engineered a GFP variant with striking properties (Patterson and Lippincott-Schwartz, 2002). This mutant is initially optically inactive. It can, however, be activated by irradiation at 413 nm and then displays fluorescence when excited at 488 nm. Eventually, after intense irradiation at 488 nm the mutant is irreversibly inactivated by photo bleaching. When Betzig returned to academic science after his post-near-field exile in private industry, he learnt about Lippincott-Schwartz’ mutant and realized that it could possibly solve the problem of finding an optimal way to combine sparse sets of fluorophores with distinct spectral properties to a dense total set of fluorophores. The simple solution would be to activate a very small and thus sparse, random subset of GFP mutant molecules in a biological structure by low-level irradiation at 413 nm. Subsequent irradiation at 488 nm would then be used to determine the positions of the members of the sparse subset at super-resolution, according to Eq. 5 above. When the first subset had been irreversibly inactivated by bleaching, a second small subset could be activated and the positions of its members determined at high resolution, and so on until all subsets had been sampled and used to determine the structure under authentic super-resolution conditions. This fulfilled both the condition of only a sparse subset being observed at a time, and the condition of high-frequency (dense) spatial sampling in order to fulfill the Nyqvist and Shannon theorems, as illustrated in Fig. 8.