I am really confused about this! So people thought that as wavelength increases for electromagnetic radiation, intensity of radiation increases but this would mean that people would melt if exposed to any radiation higher than visible light. But then they did an experiment and they sketched the graph of the experiment which is the true graph of intensity vs wavelength. I get everything up to this point but I would very much appreciate it if someone explains to my why intensity would decrease after the peak intensity at the visible light range? What does it have to do with quantification of energy? Also, what is the proper derivation of E=hf? I really want to have a complete understanding of this because it is very important to understand Einsteins explanation of the photo electric effect and the the rest of quantum mechanics. Thank you!