High-speed footage of a Bunsen burner flame turning red when a sample of strontium chloride is atomised and sprayed into it. The strontium (II) ions absorb energy from the flame and the electrons of the strontium ions make transitions between energy levels. Strontium ions in excited states can transition to lower energy levels and this is accompanied by the emission of light of specific wavelengths. For strontium, the emission of red wavelengths at 606 nm and several wavelengths between 636 and 688 nm are most apparent.