Transcription factor that binds DNA to G box 5'-CACGTG-3' and, to a lower extent, to E-box 5'-CANNTG-3' in vitro. Binds to chromatin DNA of the FT gene and promotes its expression, and thus triggers flowering in response to blue light. Homodimer (Probable). Interacts with IBH1 (PubMed:23161888). Binds reversibly to CRY2 after blue light illumination (PubMed:18988809, PubMed:24780222, PubMed:24130508). Expressed constitutively in roots, leaves, and stems. Accumulates strongly in response to blue light due to reduced preventing 26S proteasome-mediated degradation in an ADO1/ZTL and ADO2/LKP2 dependent manner, but levels decrease in the absence of blue light via 26S proteasome degradation (at protein level). The blue light-mediated interaction between CRY2 and BHLH63/CIB1 is used to design an optogenetic control of target proteins or organelles.