The Spectral Similarity Index, or SSI, addresses problems with existing indices, such as CRI, that have become evident with the emergence of solid-state lighting (SSL) sources such as LED’s.

In contrast to the relatively smooth, continuous spectral power distributions of blackbody emission, tungsten incandescence, and daylight (and the ISO standardizations of these sources), many solid-state sources are characterized by peaky, discontinuous, or narrow-band spectral distributions.

Well, solid state, aka led sources are exactly much better than fluos or such. They are smooth, except some blue peak.

These spectral distributions can wreak havoc with color rendition (by both film and digital sensors), since film and digital cameras are all expressly designed to work with, and are indeed optimized for, standard tungsten and daylight. This problem is exacerbated by the fact that CRI, for example, is based on human color sensitivity rather than camera sensitivities, and is determined by the rendering of a small number of test colors, which are mostly of low saturation and do not include skin tones. The TLCI measures rendering by an idealized three-chip camera, which does not adequately account for the differing spectral sensitivities of single-chip cinema- or still-camera digital sensors.

Well, make it account, but in reality of design ARRI cameras, for example, have sensitivity quite close to human vision. We have topic.

For these reasons, SSI is not based on human vision, or any particular real or idealized camera, and does not assume particular spectral sensitivities. Rather, it measures how close a given spectrum is to a specified reference spectrum, such as tungsten or daylight. It is a single value representing the quality of the curve fit to the reference spectrum, and indicates the predictability of color rendering with the given source. SSI is scaled so that a score of 100 indicates a spectral match; high values indicate predictable rendering by most cameras (as well as “quality” of visual appearance). Low values may produce good colors with a particular camera but not with others. SSI is useful for cinematography, television, still photography, and human vision.

Sounds real nuts, yes, exact curve matching with black body spectrum warranty good colors. But it is not requirement, exactly due sensitivity curves and human perception.

https://www.oscars.org/science-technology/projects/spectral-similarity-index-ssi