发射光谱是当一个元素被激发（加热）时，在相对于电磁辐射的每一个频率中，某些频率的辐射强度增加的现象。

当化学元素中的电子被激发时，它会跃迁至能量较高的轨道上，而当这个电子离开激态，返回低能量的轨道时，能量会被再辐射出来，分离出来的发射谱线就是所提到的波长。注意，辐射的谱线频率会比原来的频率宽一些，这是谱线致宽的效应。

这个项目虽然经常提到可见光的发射光谱，但实际上它存在于整个的电磁频谱，从低能量的无线电波到高能量的γ射线都有。

发射光谱可以用来确定材料的组成，因为在周期表上的每一种化学元素都有各自不同的发射光谱。例如，分析接收到的光谱可以确认恒星的组成。

The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to an atom or molecule making a transition from a high energy state to a lower energy state. The energy of the emitted photon is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify the elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances.