​Carotenoids represent a large class of terpenoids characterized by an extensively conjugated polyene chain. The conjugation system imparts carotenoids with excellent light absorbing properties in the blue-green (450–550 nm) range of the visible spectrum. The light-absorbing properties of carotenoids have been exploited by photosynthetic organisms to extend the range of light absorption by the photosynthetic apparatus beyond that of chlorophyll.(1) Following light absorption the carotenoid excited state undergoes excitation energy transfer to chlorophyll.(2) In addition to their role as accessory pigments, carotenoids protect against excess light by quenching both singlet and triplet state chlorophylls. In plants oxygenated carotenoids, known as xanthophylls, provide additional photoprotective functions by nonphotochemical quenching (NPQ) of chlorophyll fluorescence.