: any of various pigments (such as carotenoids and phycobilins) that are found in photosynthetic cells and absorb light of wavelengths not absorbed by chlorophyll a Algae at deep regions receive mostly green and blue light and must have special accessory pigments capable of absorbing these wavelengths efficiently.— James D. Mauseth, Botany: An Introduction to Plant Biology, 2009 Note:
The light energy absorbed by accessory pigments must be transferred to chlorophyll a before it can be used in photosynthesis.