Each pigment has a light-catching array of atoms, which are often joined by alternating single and double bonds. In a pigment molecule, an input of energy destabilizes the electron distribution in the light-catching array. Within a minute amount of time, the excited electron return to a lower energy level, the electron distribution stabilizes, and energy in emitted in the form of light. A fluorescence is when a destabilized molecule emits light when it reverts to its more stable configuration. Excitation will only occur when the quantity of energy of an incoming photon matches the amount required to boost an electron to the higher energy level.
Chlorophylls are the main pigments in every marginal photoautotroph group with the exception of one.
Chlorophyll a is a green pigment that absorbs red and blue-violet light. Chlorophyll b absorbs wavelengths in the blue and red-orange parts of the spectrum. This chlorophyll occurs in plants, green algae, and a few photoautotrophic bacteria. They reflect wavelengths which are red, orange, and yellow. Usually the carotenoid molecule's backbone has a carbon ring at each end.