How to map RGB LED to wavelengths?
Figure 1. Apparent colour mixing when adjusting intensities of RGB LEDs.

We tend to think that by mixing RGB intensities that we can generate any colour or wavelength. This is, in fact, not true. What happens is that due to the way the eye is designed that we have the perception of the new wavelength.

The human eye can distinguish three broad wavelength bands - short, medium and long - with the three different cone types. These sensors correspond roughly to red green and blue.



Figure 2.

The perception of colour is due to the relative signal strength detected by each cone.


  Most importantly, I was wondering if it was possible to map RGB values to a specific wavelength so that I could graph output voltage values against wavelength values.


No. The wavelengths emitted by your RGB LED won't change - only their relative intensities. (They might shift slightly due to temperature at higher brightnesses but not as much as your question suggests.)