The light-harvesting complex (LHC) functions as a light receptor, it captures and delivers excitation energy to photosystems with which it is closely associated (By similarity). Mediates rapid phosphorylation and migration of LHCII-PSII to photosystem I (PSI) after transition to state 2 (red) light conditions, thus leading to the formation of PSI-PSII-LHCII and PSI-LHCII supercomplex to balance the relative excitation of PSI and PSII (PubMed:23995216, PubMed:23888908, PubMed:25194026, PubMed:26392145). Involved in the production of reactive oxygen species (ROS) and stomatal closure upon abscisic acid (ABA) treatment. Required to prevent water loss (By similarity). Binds at least 14 chlorophylls (8 Chl-a and 6 Chl-b) and carotenoids such as lutein and neoxanthin. The LHC complex consists of chlorophyll a-b binding proteins (By similarity). Component of LHCII trimers made of LHCB1, LHCB2 and LHCB3 subunits (PubMed:23888908, PubMed:23995216, PubMed:25194026). Associated with super- (PSI-LHCII and PSII-LHCII) and mega-complexes (PSI-PSII-LHCII) containing LHCII and both photosystem (PS)I and PSII, in state 2 (red) light conditions (PubMed:23995216, PubMed:23888908, PubMed:25194026, PubMed:26392145). Accumulates at stronger levels in low light than in normal or high light; more expressed in growth chamber conditions than when grown in the field (PubMed:22236032). Repressed in leaves exposed to desiccation, cold and high irradiance via a metalloprotease-dependent proteolytic process (at protein level) (PubMed:23598180). Photoregulated by reversible but rapid phosphorylation by STN7 of its threonine residues under state 2 (red) light conditions (PubMed:23995216, PubMed:23888908, PubMed:26392145). Dephosphorylated by PPH1 in state 1 (far red) light conditions (PubMed:20176943, PubMed:23995216, PubMed:23888908, PubMed:26392145). Phosphorylation triggers the formation of the PSI-LHCII supercomplex (PubMed:26392145). In plants silenced with microRNAs, functional LHCII thylakoid protein complexes where LHCB2 is replaced by LHCB1. However these LHCII complexes are impaired in light state transitions, leading to stunted growth in high light. Belongs to the light-harvesting chlorophyll a/b-binding (LHC) protein family.