# Does an electron move from one allowed orbit to another only when it absorbs or emits a fixed amount of energy?

A given quantum of energy, $h \nu$, is present in a single photon (a "packet" of light).
• Energy input of $h \nu$ describes the energy given by one absorbed photon that causes excitation of an electron to a higher energy level, based on the frequency $\nu$.
• Energy output of $h \nu$ describes the energy in one emitted photon that was due to relaxation of an electron from a lower energy level, based on the frequency $\nu$.