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 the impact of supplemental multispectral light-emitting diode (LED) lighting at night on the growth and essential oil production of Ocimum gratissimum L. (OG) cultivated in a net house over 15 weeks. Nine lighting treatments were established, combining red (R) and blue (B) lights with ultraviolet-A (UV-A), green (G), or far-red (Fr) lights. Supplemental lighting was delivered for 4, 6, and 8 hours per night at irradiances of approximately 100 and/or 80–120 µmol·m⁻²·s⁻¹. Gas chromatography/mass spectrometry with flame ionization detection (GC/MS-FID) identified 21–28 essential oil compounds, predominantly phenylpropanoids (59.4–71.2%), with eugenol (58.5–69.8%), (Z)-β-ocimene (10.2–12.1%), and germacrene D (7.6–12.1%) as major constituents. While the essential oil showed weak antimicrobial activity against Candida albicans, all nine lighting treatments significantly enhanced fresh biomass and essential oil yield (p < 0.001) compared with the control. The optimal supplemental lighting treatment (F2; 71R:20B:9UV-A, 100 µmol·m-2·s-1, 6 h/day) produced the highest fresh biomass (13.07 tons/ha), essential oil yield (31.39 L/ha), and eugenol yield (21.09 L/ha). These results underscore the strong influence of spectral composition and exposure duration on plant productivity and suggest that customized LED lighting strategies can substantially enhance both biomass and oil quality in OG cultivation.