> ...Can't a simple prism be used to separate the spectrum?
>
> Sure. Early spectrophotometers mechanically swept
> a prism-generated spectrum.

A prism is fine but dearer and harder to do well compared to a
diffraction grating.

IR & or UV are liable to be absorbed by various media you may choose
to use, and with the possibility of deep holes in some places - about
the inverse of what you are looking for when you display an LEDs
spectrum.
--=20
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