As schematically illustrated in Figure 11.1, some types of molecules in the ground state are able to absorb high-energy light (e.g., blue light) to jump to a higher level of energy state, which is called “excited state.” The energy level of the excited molecule, represented by the darker ball, is shown as the top black line in the diagram. Some of the energy from the darker molecule is lost internally (represented by the squiggly arrow in the diagram). The molecule then emits a photon with less energy, which is a wave on the right side in this example.