Flame photometry is a technique that uses the intensity of light emitted from a flame to determine the concentration of certain metal ions in a sample. When a sample is introduced into the flame, the metal ions are atomized and excited. As they return to the ground state, they emit light of characteristic wavelengths. The intensity of light emitted can then be measured to determine the concentration of the metal ions. Flame photometry is used to analyze samples for concentrations of ions like sodium, potassium, calcium, and lithium. It has applications in analyzing body fluids and determining metal concentrations in materials like cement.