These are accessory pigment molecules that cascade light energy to 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 and therefore appear red-orange in color. They are found in all plants and certain photosynthetic bacteria. Carotenoids are divided into two groups, carotenes and xanthophylls. Carotenes (C40H56) are polyunsaturated hydrocarbons containing no oxygen and include pigments such as α-carotene, β-carotene and lycopene. They give the 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 the outer fourth shell electrons are in overlapping p orbitals. This overlap produces a system of π bonds with delocalized electrons. Delocalized electrons are free to move and are therefore more easily lost because less energy is required to raise them to an excited state. Shorter wavelengths towards the blue end of the spectrum with lower energies are absorbed due to the lower energy.