Sunlight is absorbed by chlorophyll molecules. Chlorophyll is a porphyrin in that nitrogen atoms are coordinated to a magnesium ion instance for it is a magnesium porphyrin. This dissimilarity with a hemi in that the nitrogen atoms are synchronized to an iron atom to built an iron porphyrin. Green plants hold two parts of chlorophyll molecules, chlorophyll a and chlorophyll b, which vary slightly in structure and in the wavelength of light they can absorb. Whereas light is trapped by chlorophyll molecules straightly, several accessory pigments also exist which absorb light and pass the excitation energy on to chlorophyll molecules. Thus the carotenoids are significant accessory pigments in green plants whilst phycobilins are accessory pigments in photosynthetic bacteria. This pigment absorbs light at wavelengths dissimilar from in which of chlorophyll and so act together to maximize the light harvested.