Chlorophyll is excited by photons of light.
This means when a photon of light comes into contact with a chlorophyll molecule, the chlorophyll absorbs the energy from the photon. This absorption causes an electron within the chlorophyll molecule to jump to a higher energy level, thus putting the chlorophyll in an "excited" state. This excited state is crucial for the process of photosynthesis, as the energy is then used to drive the reactions that convert carbon dioxide and water into glucose.
