The pigment present in the photosystems alters the absorption spectra. Due to different wavelengths of light being absorbed by the pigment, more wavelengths of light can be absorbed by the antenna complex and subsequently transferred to the reaction centre.
Light harvesting complexes are able to contain different pigments, typically: chlorophyll a, chlorophyll b, and carotenoids. This allows a wider range of wavelengths of light to be absorbed, increasing the energy captured.
Each pigment molecule has a slightly different absorption spectra, as each pigment binding site is unique. This is because the π-electron system on the pigment is easily altered by the environment, causing each molecule to absorb light slightly differently. These changes in absorption also allow Förster resonance energy transfer (FRET) to occur, with the electron excitation energy levels decreasing towards the reaction centre. This ensures the directionality of FRET is correct, with excitation energy flowing towards the reaction centre.