Study on Spectral Response of Saffron (Crocus sativus L.) at Different Leaf Ages and Evaluation of Photosynthetic Energy Efficiency of Narrow-Band LED Spotlights

Abstract

Leaf photosynthesis largely determines the daughter corm yields in vegetative growth for saffron (Crocus sativus L.). Most of the previous researches focus on the spectral response in various species, but research on saffron leaves at different leaf ages is lacking. In this study, the action spectrum based on photosynthetic photon flux density (PPFD) and irradiance were distinguished and interpreted. The optical properties and photosynthetic performances of leaves were, respectively, investigated at two leaf ages, dependent on customized narrow-band LED spotlights from 380 nm to 780 nm with an interval of 20 nm and a band width of 10 nm. The younger leaves were characterized by higher reflectance and transmittance values at 500−600 nm, resulting in lower absorptance compared to the older leaves. The spectral response curves including the action spectrum and quantum yield for younger leaves were higher than the older, but their relative curves displayed coincidence. The spectral response curves exhibited two peaks at 440 and 640 nm, but no obvious troughs between 500 and 600 nm were observed. Nevertheless, the photosynthetic energy efficiencies of spotlights demonstrated very low values in the green/yellow region. Accordingly, more attention should be paid to green and yellow LED lighting during the vegetative stage for saffron, as well as improving their manufacturing technology.