They are accessory pigment molecules that cascade light energy onto the primary pigments. Carotenoids absorb wavelengths in the blue and green region of the visible spectrum (400-550 nm) and reflect wavelengths of 590-650 nm, so they appear orange-red in color. They are found in all plants and some photosynthetic bacteria. Carotenoids are divided into two groups, carotenes and xanthophylls. Carotenes (C40H56) are polyunsaturated hydrocarbons that do not contain oxygen and include pigments such as α-carotene, β-carotene, and lycopene. They give orange color to carrots and autumn leaves. Xanthophylls (C40H56O2) contain oxygen and include lutein and zeaxanthin. Carotenoids contain alternating carbon-carbon double bonds and single bonds, forming a conjugation system in which electrons in the outer fourth shell are in overlapping p orbitals. This superposition produces a system of π bonds with delocalized electrons. The delocalized electrons are free to move and therefore are lost more easily because less energy is needed to bring them to the excited state. Shorter wavelengths towards the blue end of the spectrum with lower energies are absorbed due to the lower energy