Determine the energy emitted if one mole of strontium ions undergo the transition at 687 nm. The bright-red color of highway safety flares comes from strontium ions in salts such as Sr(NO3)2 and SrCO3. Burning a flare produces strontium ions in excited states, which then emit red photons at 606 nm and several wavelengths among 636 and 688 nm.