A modern 35mm film scanner for home

Can confirm. I used to write software for them.

The issue with LEDs, is very pure colors. That’s actually a bit of a problem, with film scanners. You need a smooth curve, and it needs to extend out a bit. You don’t want areas of color being missed.

The Coolscans had a light color response (think the “levels” screen, in Photoshop) that looked like three steep hills, with minimal overlap, but they were able to make them wider than a “pure” LED. Coherence is a feature of LED lighting.

Most previous light sources used filters over a white light, and they looked “sloppier,” with a lot more overlap, so there was more coverage. We had to correct for the unusual color coverage of LEDs.

One of the things that the Coolscan did well from a hardware perspective was that it made the transport sprocketless which allowed damaged film to be easily scanned, and it also allowed non-standard formats to be scanned easily as well. I’m curious if they have a sprocket driven system for this or if it utilizes a similar system as the Coolscan - I’ve used many scanners and the Coolscan is still the best/most convenient because of being able to just sequentially scan an entire roll of negatives.

I assume the LEDs were matched to the typical pigments used in films though? Because otherwise metamerism just wouldn't work, RGB mixed to some CCT is not white light and can't illuminate arbitrary pigments with any kind of good color reproduction.

I assume so. The folks that designed the scanners were no slouches. I suspect that they never completely turned off any LEDs, so there was always some deliberate “slop.” With LEDs, however, you can explicitly control that. They probably had some kind of filter, also. I never took one apart, though.

I got the response curves by feeding in a special slide with a diffraction grating.

The curves were markedly different from an incandescent light source.