The Carotenoid Reflectance Index 2 (CRI2) is a carotenoid‑sensitive index that uses reciprocal reflectance in a green band and a red‑edge or NIR‑adjacent band to enhance sensitivity to leaf carotenoid concentration. By leveraging the spectral contrast between carotenoid absorption and a more weakly absorbing band, CRI2 supports refined assessment of carotenoid dynamics and plant stress independent of structural variation.