Absorption Spectrum

Absorption, in this context, means the complete retention of incoming light energy by a pigment molecule, as opposed to that light being reflected away or transmitted straight through. Since different pigments absorb different wavelengths to different degrees, plotting the amount of light absorbed against wavelength for a given pigment produces a curve called that pigment's absorption spectrum. For chlorophyll specifically, both chlorophyll a and chlorophyll b absorb light strongly from the blue and the red regions of the visible spectrum, while absorbing comparatively little from the green-yellow region in between - which is exactly why healthy leaves look green to us, since green light is the wavelength range chlorophyll reflects rather than absorbs. Chlorophyll a itself does not have one single absorption peak but several distinct ones, corresponding to slightly different molecular environments within the thylakoid membrane: peaks around 670-673 nm, 680-683 nm, and 695-705 nm. Two of these specific forms are functionally named for their peak wavelength and given a special role: chlorophyll a680, called …