"Here I have plotted intensity versus wavelength. Long wavelength is low energy. Energy is increasing from right to left. And what we see is a family of nested curves each taking a different plate voltage.

Low voltage gives us low intensity. High voltage gives us high intensity. We see this whale-shaped background which we refer to as the continuous spectrum or "bremsstrahlung." And then once we reach a critical voltage beyond which we start to see this second set of lines here, which I have indicated in fuchsia.//

And this is the characteristic spectrum, and it is quantized. It is not continuous. We have discrete values of wavelength associated with energy transitions within the target. And those transitions are prompted by the ejection of inner shell electrons..."