Discrete spectrum
![Spectrum of sunlight above the atmosphere (yellow) and at sea level (red), revealing an absorption spectrum with a discrete part (such as the line due to O2) and a continuous part (such as the bands labeled H2O).](/Images/godic/202501/09/Solar_Spectrum0554.png")
![Acoustic spectrogram of the words](/Images/godic/202501/09/Oh_No_Girl_Spectrogram0554.jpg")
A physical quantity is said to have a discrete spectrum if it takes only distinct values, with positive gaps between one value and the next.
The classical example of discrete spectrum (for which the term was first used) is the characteristic set of discrete spectral lines seen in the emission spectrum and absorption spectrum of isolated atoms of a chemical element, which only absorb and emit light at particular wavelengths. The technique of spectroscopy is based on this phenomenon.