Triggers photoperiod-monitored flowering by repressing PHYB-dependent flowering negative regulation, probably through physical interactions with PHYB and CO. Component of a red light-dependent nuclear complex made of PHL, PHYB and CO. Interacts directly with PHYB and CO; CO binding requires the presence of PHYB. Circadian clock-regulated subcellular localization. During the night, mainly present in the cytoplasm. During the day, moves and accumulates progressively in the nuclei. Mostly expressed in cotyledons and leaves, both in mesophyll and vasculature cells. Also present in roots, hypocotyls and shoot apices. Repressed post-transcriptionally by white light (at protein level). Late flowering, especially under long-day conditions (PubMed:24127609, PubMed:24614229). Reduced expression of FT and SOC1 (PubMed:24127609).