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It seems like an alternative would be a broad-spectrum white light source with narrow-band color filters that correspond to similar wavelengths to the LEDs mentioned. That would require simpler light source but more costly subtractive filtering.

All those old-school minilabs pre-blue LEDs...they must have used white light sources and filters, right?

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Being able to tune the intensity ratio of the bands, especially with source age, is nice so that everything's in the middle of the sensor's dynamic range ... optical filters can be pretty cheap at scale or as surplus, but, well behaved broadband light sources aren't so easy to find.

Author here, I was curious about this too since I would have expected most film scanners from the 90s-2000s to use incandescent light sources if high-CRI light was really the way to go. Minilabs that made direct optical prints to RA-4 paper did use white light sources with filters, since RA-4 paper is already only sensitive to narrow bands of light. In the mid-90s, Fujifilm and others introduced minilabs that could also scan film and produce prints from digital files. These all used RGB LEDs to scan the film, and they must have had a very good reason to since blue LEDs were barely ready for commercial use at the time.

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