Just an update. Digging around I found this master's thesis published last year:
UG ETD Template (uoguelph.ca) The author concludes (
contra this study):
"UV radiation reduced total terpene concentrations and the size and proportion of apical inflorescences relative to other inflorescences on the plant in both cultivars. Cannabis growth (i.e., height increases and increases in number of nodes) was generally suppressed by UV radiation
"UV radiation had no commercially relevant benefits to inflorescence cannabinoid content, and the total terpene concentrations decreased linearly over the range of UV-PFDs evaluated"
This study (Cannabis Yield Increased Proportionally With Light Intensity, but Additional Ultraviolet Radiation Did Not Affect Yield or Cannabinoid Content) noted: "Although there were no UV spectrum effects on total equivalent Δ9-tetrahydrocannabinol (T-THC) content in leaves, the neutral form, THC, was 30% higher in UVA+UVB vs. control. While there were no LI effects on inflorescence T-THC content, the content of the acid form (THCA) increased by 20% and total terpenes content decreased by 20% as LI increased from 350 to 1400 μmol m-2 s-1. High LI can substantially increase cannabis yield and quality, but we found no commercially-relevant benefits of adding supplemental UV radiation to indoor cannabis production."
This one stated: "The total equivalent Δ9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD) concentrations also decreased in LT inflorescences with increasing UV exposure level. While the total terpene content in inflorescences decreased with increasing UV exposure level in both cultivars, the relative concentrations of individual terpenes varied by cultivar. The present study suggests that using UV radiation as a production tool did not lead to any commercially relevant benefits to cannabis yield or inflorescence secondary metabolite composition. " and explained:
"Preliminary controlled-environment studies, that were done about three decades ago, also alluded to the potential for UV to increase Δ9-THC concentration in cannabis foliar and floral tissues (
Fairbairn and Liebmann, 1974;
Lydon et al., 1987). However, the concentration of Δ9-THC in mature female cannabis inflorescence tissues (hereafter, inflorescence) has increased substantially over the past decades, with contemporary genotypes having ≈10 times higher Δ9-THC concentrations than the genotypes used in these older studies (
Dujourdy and Besacier, 2017). Therefore, modern cannabis genotypes may function nearer to cannabis’ maximum capacity for producing Δ9-THC; which could impede their ability to further increase Δ9-THC production under an abiotic stress such as UV exposure, relative to older genotypes. "
Maybe we are near max D9 THC levels we can coax out of the plant no matter what you do.
I'm trying to drill down on the levels and spectra used in these studies to compare to what I am getting with my Solarcure 24" tubes and will update. For now, I am discontinuing UVA/UVB supplementation until I am more comfortable, especially with the potential terpene reduction.
