The light-harvesting complex (LHC) functions as a light receptor, it captures and delivers excitation energy to photosystems with which it is closely associated. Seems involved in the function of the photosystem I in low light conditions, when other LHCA proteins are less abundant. Required, together with LHCA5, for the formation of a full-size NAD(P)H dehydrogenase-photosystem I supercomplex (NDH-PSI) that triggers cyclic and chlororespiratory electron transport in chloroplast thylakoids, especially under stress conditions (e.g. increased light intensity). 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 (PubMed:19903870). Homodimer. Binds pigments (By similarity). Element of the NAD(P)H dehydrogenase-photosystem I supercomplex (NDH-PSI) (PubMed:19903870). The N-terminus of the protein extends into the stroma where it is involved with adhesion of granal membranes and post-translational modifications; both are believed to mediate the distribution of excitation energy between photosystems I and II. Photoregulated by reversible phosphorylation of its threonine residues. Slightly lower NDH activity in immature leaves. No chlorophyll fluorescence increase in mature leaves. Smaller version of the NAD(P)H dehydrogenase-photosystem I supercomplex (NDH-PSI) supercomplex (PubMed:19903870). In the double mutant lhca5 lhca6, drastic reduction of NDH subunits accumulation upon increased light intensity (PubMed:21278308). Belongs to the light-harvesting chlorophyll a/b-binding (LHC) protein family.