Influence of Light Spectra on the Production of Cannabinoids

Abstract

In recent years, more attention has been paid to cannabis from both medical and political points of view. This study investigates the influence of 5 different light spectra on the active substance content in THC-poor hemp of the Alessia chemotype II variety. The focus is on comparing conventional growing under metal halide lamps with growing under high-pressure sodium (HPS) vapor lamps with regard to different spectra of LED lighting modules. Growing was carried out in 10 growing boxes under controlled and mostly identical conditions for all boxes. The photoperiod during the vegetative phase was 18 h light and photosynthetic photon flux density ∼520 μmol⋅m⁻² s⁻¹. The flowering phase was 12 h light and ∼540 μmol⋅m⁻² s⁻¹. During the experiment, CO₂, temperature, and humidity were measured and logged. Additionally, weekly measurements of chlorophyll, electric conductivity of the fertilizer, activity measurement (salt content) of the soil, and pH value of the soil were checked. The content of cannabinoids was measured by high-performance liquid chromatography (HPLC). Plant height and growth were monitored during the whole experiment by cameras taking pictures every 30 min and loading them onto a cloud storage platform. Cannabinoid content was measured using HPLC. Plant wet weight was determined at the end of the experiment and showed that plants under the high pressure lamp treatment had less flower weight than those under the LED treatment. In conclusion, it could be shown that certain LED spectra can considerably increase the amount of cannabinoids with respect to conventional illumination (HPS).