UC Davis

Basil (Ocimum basilicum L. Genovese) is a highly valued and economically important herb with significant culinary qualities. The quantity of light supplied to plants, including both light intensity and photoperiod, plays a critical role in regulating plant morphology and biomass accumulation. Optimizing these factors can simultaneously enhance yield and resource efficiency. This study assessed the effects of constant versus gradually increasing light intensity and photoperiod on basil growth, physiology, and light use efficiency (LUE), while maintaining an equivalent average daily light integral (DLI) over the 24-day growing period. Four different treatments were applied in a climate-controlled growth chamber: (CIP) constant light intensity (300 μmol m^-² s^-¹) and constant photoperiod (16 h), (CIDP) constant light intensity with a dynamic photoperiod (14-16-18 h), (DICP) dynamic light intensity (200-300-400 μmol m^-² s^-¹) with constant photoperiod, and (DIP) dynamic light intensity (200-300-400 μmol m^-² s^-¹) and photoperiod (14-16-18 h) over time. In comparison to CIP, treatment DIP resulted in a 9% increase in both dry weight and LUE, and a 19% increase in non-destructive chlorophyll content, whereas stomatal conductance was 25% higher in CIP. CIDP exhibited the lowest values for leaf area, fresh weight, dry weight, LUE, destructive chlorophyll and carotenoid content, and non-photochemical quenching (NPQ). These results suggest that dynamic light strategies can improve LUE and dry matter accumulation under comparable average DLI conditions. Future research should investigate whether these responses are associated with any changes in postharvest quality, processing characteristics, and the temporal dynamics of secondary metabolites to further refine lighting strategies for indoor farming.