Spectral rendering, part 1: Spectra

In my previous blog post, I explained spectral radiometric quantities and a few basics of spectral rendering.
In this blog post series, we dive into much more detail on spectral rendering.
I present a specific way to implement it in a real-time path tracer and demonstrate what advantages it brings compared to RGB rendering.
RGB rendering is still by far the most common way to do rendering.
Colors just get multiplied component-wise, i.e. red times red, green times green and blue times blue.
That is a poor approximation of our physical reality.
In practice many of the issues that this causes are covered up by manual color grading.
Spectral rendering offers more accurate color reproduction, more independence of the choice of color spaces, support for unusual light spectra and all that at a rather negligible computational cost.
It is not an obscenely expensive theoretical avenue for offline rendering, but a viable addition to real-time renderers (rasterizers and path tracers alike) that can be made to work with existing assets.
If you do not believe me, maybe these posts can change that.
It does not hurt to read the series on radiometry first, but in principle, this series is self-contained.
This first part focuses on what kinds of spectra we need to specify a scene and how we can get them.