Light emission by fluorescence. In this example, an electron jumps from the lowest to highest energy level by absorbing a high-frequency (eg, blue) photon (1). The electron drops to a slightly lower, intermediate energy level through nonradiative processes or by emitting a low-energy (eg, infrared) photon (2). Eventually, the electron drops to its original energy level, emitting a photon of slightly lower frequency (eg, green) than the one it absorbed (3).