There is a machine that allows you to dial in a wavelength and out comes
a beam of light which has the wavelength you set. It is called a monochronometer. One could use such a device to test the sensitivity of various photosensitive
materials to various wavelengths of light. I have considered doing this but
that would make fun (fine art photography) too much like work (physics). ;-)
These machines can be found in physics departments of colleges among other
places.
Bob Schranmm