A line is a dark or bright band of color in a spectrum. It can be formed by the emission of light from a narrow region, such as an atom in an excited state. The frequency of light emitted by an atom depends on its energy level, so atoms emit light at specific frequencies. These frequencies correspond to specific energy levels for different atoms, which appear as lines in the resulting spectrum.
The emission spectrum of hydrogen gas, for example, shows lines at wavelengths that correspond to the energy levels of hydrogen ions (H+). If you excite hydrogen gas by heating it or passing it through an electric field, the atoms will absorb energy and jump to higher-energy orbits around their nuclei. The electrons in those orbits then emit photons with specific wavelengths as they fall back down to lower orbits.
Last modified: September 19, 2022