blue light signaling pathway photoreceptor activity red or far-red light signaling pathway far-red light signaling pathway red light signaling pathway obsolete signal initiation by light true biological_process This term was made obsolete because the meaning of the term is ambiguous. GO:0023037 signal initiation by light OBSOLETE. The process in which a light signal causes activation of a receptor. 2010-02-16T09:30:50Z