These processes come through light interaction with species and cultivars, which mainly depend on its irradiation, enhancing stressful or non-stressful events for plants . Despite energy sources for photosynthesis, light can simultaneously act as a stress factor as plant response to light mainly depends on the lighting environment, genotypes, cultivation practices, etc. .Excess light increases evaporation and photoinhibition, resulting in dehydration in leaf tissue, causing reduced photosynthetic production.Plants use the wavelength of red light to accumulate carbohydrates and nutrients , red and blue for electron excitation in the photosynthesis process and, blue and UV to synthesize carotenoids and anthocyanins .Evidence showed that high intensities of UV-B radiation cause stress to plant by inducing DNA damage, photoinhibition, lipid peroxidation, and finally, growth retardation.When plants are exposed to such light intensities or any abiotic stress condition, the demand for metabolic processes in carbon fixation increases for energy supply and reduces power by involving photosystems and electron transport chains.

This asymmetry generates reactive oxygen species , which have both signaling and toxic effects on cells . Light intensity below the compensation point also will result in a net loss of photosynthetic products, and more light after saturation point has no or negative effect on photosynthesis . Bioactive compounds are collectively known as primary and secondary metabolites, which gave aroma, color, taste even provide resistance against external biotic and abiotic stress . Evidence proved that different forms of external stress help plants produce bioactive compounds . Previous studies suggested that the R:FR ratio, the blue and UV light photoreceptors , can alter signaling pathways. These changes may affect phytohormone-mediated regulation of growth, development, physio-biochemical pathways, finally, plant root architecture , which may create partial water stress to plant. It was reported that despite the negative effect on quantum yield, plants attained a higher photosynthetic rate and biomass accumulation under supplemental UV-A radiation. This higher photosynthetic rate was due to an increase of stomatal conductance instead of the ratio of intracellular to ambient CO2 content . Besides these, ultraviolet light has a crucial role in plant response to several morphological, physiological, and secondary metabolites production, which are combinedly termed as plant photomorphogenic response .

These photomorphogenic responses mainly controlled by UVR8 by regulating gene expression relate to hypocotyl elongation inhibition, DNA repair, antioxidative defense, and phenolic compounds production . On the other hand, far-red may have an essential role in photosynthetic purposes in leaves . A high or low R and FR light ratio change the mode of action in phytochromes, converting the Pr into Pfr, or vice versa . This conversion may bring changes in gene expression related to photomorphogenesis . However, the role of UV-A and FR with the combination of other spectral bands relate to plant physiology, and morphological changes remain poorly understood. Hemp is an annual herb belongs to the Cannabaceae family has been exploited for medicinal purposes for more than 10,000 years . Living hemp plants contain cannabinoids as carboxylic acid like THCA and CBDA that decarboxylate during storage and heating transform to neutral cannabinoids such as THC and CBD . Although secondary metabolites in cannabis are mostly controlled by selecting genotypes and their phenotypic characteristics; however, some horticultural techniques, including photoperiod, lighting intensity, and quality, can change among them . Earlier in a study, theincrement of THC in cannabis was described when it was treated under controlled UV-B radiation . Ning et al. showed that UV-A and UV-B could increase secondary metabolites in Lonicera japonica medicinal plants .

For this reason, the plant treated with low dose UV mediated stress is crucial from a biotechnological and pharmaceutical point of view to increase valuable compounds . Previous studies revealed that under long-time UV treatment, all types of cannabinoids did not respond equally . It is also essential to find out the LED combination that can manipulate different targeted cannabinoids compounds by bringing in a metabolic system change in hemp plants. Besides, it is not clear which cannabinoids are directly involved with a light stress environment identified as stress markers in the hemp plant.