There is spectral rendering, where you can quantize the visible wavelengths from ~390nm to ~700nm to N discrete wavelengths instead of the standard 3 for RGB. Then if you had to model say a prism, you would get more realistic distribution of the spectrum.
Light has also property of polarization that you would need to model for increased realism. I don't know if this is being modeled in any existing publicly available rendering engines and how would you represent it exactly. Light is electromagnetic wave with two orthogonal electric and magnetic components, which may have different amplitudes and be also out of phase potentially resulting in elliptical polarization. The polarization would be a relevant propery for example to model multiple specular reflections from dielectric surfaces, or modeling polarizing filters used by photographers on cameras.
Both spectral rendering and accounting light polarization would come with the cost of performance and higher memory usage.