Cyanobacteriochrome RcaE regulates Type III complementary chromatic adaption in the cyanobacterium Fremyella diplosiphon by photoswitching between a green-absorbing dark state (P-15z(g)) and red-absorbing photoproduct (P-15E(r)). Ultrafast photodynamics of RcaE involve tautomerization of the bilin chromophore, inhomogeneity, and the generation of three primary photointermediates in the forward reaction (Lumi-G(0), Lumi-G(r), and Lumi-G(f)). The secondary photodynamics reported here show that only Lumi-G(0) evolves to P-15E(r) via spectrally similar Meta-G(o1) and Meta-G(o2) intermediates, with a protonation reaction occurring at the final step on the millisecond timescale. Reverse reaction dynamics were characterized and reveal an unusually long-lived Lumi-R-f photoproduct and a blue-shifted Meta-R-y intermediate. (C) 2015 Elsevier B.V. All rights reserved.