This spectrometer is inexpensive: https://publiclab.org/wiki/desktop-spectrometry-kit-3-0 https://publiclab.org/wiki/desktop-spectrometry-kit-3-0 The problem is

This spectrometer is inexpensive: https://publiclab.org/wiki/desktop-spectrometry-kit-3-0 https://publiclab.org/wiki/desktop-spectrometry-kit-3-0 The problem is calibration, you would need to calibrate with sources like lasers or fluorescent light with known spectral peaks. Then you could use the spectrum to calculate CRI. You are just calculating cri (which has its own issues), so even with a crude device some spectral error is ok.