Optimization of Supplemental LED Spectral Quality and Light Dose for Enhancing Biomass and Essential Oil Yield of Ocimum gratissimum L. Under Net House Condition

This study investigated optimal supplemental multispectral light-emitting diode (LED) conditions for the growth and essential oil accumulation of <i>Ocimum gratissimum</i> L. (OG) cultivated in a net house over 15 weeks. We hypothesized that supplemental lighting could increase biomass while affecting oil yield or vice versa. Nine lighting treatments were established, combining red (R) and blue (B) with ultraviolet-A (UV-A), green (G), or far-red (Fr) lights, applied for 4, 6, or 8 h/night at 80-120 µmol·m^-2·s^-1. Essential oils were analyzed by GC/MS-FID, revealing 21-28 compounds, dominated by phenylpropanoids (59.4-71.2%). Eugenol (58.5-69.8%), (<i>Z</i>)-β-ocimene (10.2-12.1%), and germacrene D (7.6-12.1%) were the major constituents. The oils showed weak antimicrobial activity against <i>Candida albicans</i>. All lighting treatments significantly enhanced fresh biomass and oil yield (<i>p</i> < 0.001) compared with the control. The optimal treatment (F2; R, B, and UV-A lights at a photon flux ratio of 71:20:9; 100 µmol·m^-2·s^-1, 6 h/night) yielded the highest fresh biomass (13.07 ± 0.71 Mg/ha), essential oil (31.39 ± 1.71 L/ha), and eugenol (21.09 ± 1.15 L/ha). These findings demonstrate the strong influence of spectral composition and exposure duration on OG productivity and highlight the potential of tailored LED strategies to improve both biomass and oil quality in cultivation systems.