Transcriptional activator involved in cell elongation. Regulates the expression of a subset of genes involved in cell expansion by binding to the G-box motif. Binds to chromatin DNA of the FT gene and promotes its expression, and thus triggers flowering in response to blue light (PubMed:24130508). Homodimer (Probable). Interacts with IBH1. Binds reversibly to CRY2 after blue light illumination (PubMed:24130508). Expressed constitutively in roots, leaves, stems, and flowers. Plants over-expressing BHLH74 show increased hypocotyl and cotyledon lengths.