The light-harvesting complex (LHC) functions as a light receptor, it captures and delivers excitation energy to photosystems with which it is closely associated (PubMed:15563470, PubMed:21806943). Seems involved in the function of the photosystem I in low light conditions, when other LHCA proteins are less abundant (PubMed:15356385). Required, together with LHCA6, 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) (Probable) (PubMed:19903870, PubMed:21278308). 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:19139095). Homodimer. Heterodimer with LHCA2 and, possibly, LHCA3 (PubMed:15356385, PubMed:17107674). Can substitute to LHCA4 to form a complex with LHCA1 (PubMed:21806943, PubMed:15563470). Binds pigments (PubMed:15563470). Element of the NAD(P)H dehydrogenase-photosystem I supercomplex (NDH-PSI) (PubMed:19903870). Induced by high light (HL) but repressed by low light (LL). Slightly inhibited by cold. 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. 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). Light emission at 684 nm upon excitation at 410 and 470 nm. Belongs to the light-harvesting chlorophyll a/b-binding (LHC) protein family.