What I want to do or know
What does the vertical scale actually represent? It seems to be based on the sum of the RGB values. This means that the only way the plot exceeds ~33% is when two adjacent channels have values of 255 which means the source data is too bright.
Why not make the 100% level correspond to the maximum level at that color? Then a 650nm laser line with an RGB value of (254,0,0) could be represented at 100% instead of around 30%.