Some objects can be emitted from the air, and the spectra formed by the light produced directly is called the emission spectrum. The emission spectrum can be divided into three different categories of spectra: line spectrum, strip spectrum, and continuous spectrum. The linear spectrum is mainly generated from atoms, consists of some discontinuous bright lines; the strip spectrum is mainly produced by the light consisting of the molecules from some intensive wavelength range; continuous spectrum, mainly produced in an incandescent solid, liquid or high pressure The gas is excited to emit electromagnetic radiation, which is composed of light of the continuous distribution of all wavelengths. When the white light passes through the gas, the gas will absorb the same light as the characteristic spectrum wavelength in its white light, and the continuous spectrum of the white light appears dark lines. At this time, the spectrum generated after the light of certain wavelengths in the continuous spectrum is referred to as a absorption spectrum. Typically, the feature lines seen in the absorption spectrum will be less than the linear spectrum. When light is irradiated onto the substance, non-elastic scattering occurs, except for the same elastic component (Rayleigh scattering) as the excitation light wavelength, there is a short component than the exciting radio wave, the latter The phenomenon is collectively referred to as Raman effects. 