Light is a concentration of photons. In an atom, there are different electron levels that electrons remain in. When the atom is in a normal state, certain electrons will encounter photons that have just the right amount of energy to allow them to jump to a higher state. The photon is absorbed during this process. This absorption puts an atom into what’s known as the “excited state.” If the atom doesn’t continue to absorb photons, in order for the electron to drop down an energy level, it needs to emit a photon in a process called emission (which was the same amount of energy it took to make the electron go up an energy level).