Explain what happens when a photon hits an atom if it has the correct amount of energy. 7. Intensity is related to the number of photons corresponding to a particular transition. In the graph below, this shone as the height of the peaks in the Helium Spectrum. Explain the color emitted by Helium by matching up the wavelengths with visible colors (Blues around 450 nm and Reds around 750 nm. You can use one of the CH.5 ppt slides for a more precise correlation)