Principle underlying the quantitative analysis:
In flame photometry, the thermal energy from flame is utilized to convert the analyte within gaseous atoms and then to excite them to higher energy level. Since the excited atoms return to a state of lower energy, radiation of wavelength features of the element is emitted. The intensity of the emitted radiation is associated to the concentration of the element present, creating the basis of the quantitative analysis through flame photometry.
As we measure the emission spectrum of the atoms which were excited using the thermal energy of flame, the methods is known as flame atomic emission spectroscopy (FAES).