Plotting like this is an art. It's about presenting the data in a way that makes it easier to understand the data. As such, you have to account for what story you are trying to tell the reader.
The first question I would have is whether the curve fit is worth showing. You have 5 data points in your experimental data, and apparently the story you are trying to tell is that the experimental data lines up with the theoretical data. However, that's not the story I get. While the datapoints themselves line up well, the curves are almost completely unrelated in every way. The story the curve tells is "these light sources are completely different from each other," and I have to look deeper to realize that the measured points are actually really close, it's only the artificial curve-fit that's far. Ditch the curve fit, and instead only show the data points themselves with no line between them. Switch to a bar chart if it's more comfortable.
Also, if you are presenting theoretical data and real data on a chart, label them very explicitly. You never want a customer of your presentation to mistake one for the other. It actually took me a while to realize what was going on because it was hard to figure out which data was real.
Fix those, and you can show graphs which compare different units. However, you want to make it very clear why you were doing so, and why you didn't convert ones data into the other's units.