## 3 Light Effect on Growth and Development of _C. sativa_
### Light Spectrum in Cannabis Growth, Development, and Metabolism
Treatments L4, L6, L8 (R5/B2), and L11 displayed increased node numbers and osmolyte content--proline, ascorbic acid, total soluble carbohydrates (TSC), and sucrose--indicating greater branching, infloresances, and cannabinoid accumulation [37; 69] (Table 1). This pioneering study provides a crucial foundation for future research, steering the optimization of light compositions to cultivate _C. sativa_ with ideal phenotypes. Notably, incorporating green light into other spectra enhanced osmoprotectant molecules compared to red and blue combinations alone, heralding a new era in precision agriculture for _C. sativa_ cultivation. The research underscores the significant impact of light quality on the morphophysiological traits of industrial _C. sativa_[70]. A key study investigated the effects of different light spectra--white (WL), blue (BL), red (RL), and a 50:50 red-blue mix (RBL)--on _C. sativa_'s morphology, gas exchange, and antioxidant capacity. The results were remarkable: BL increased shoot fresh biomass by 15.1%, shoot dry biomass by 27.0%, leaf number by 13.7%, stem diameter by 10.2%, root length by 6.8%, and chlorophyll content by 7.4% compared to WL. Additionally, BL significantly improved net photosynthesis, stomatal conductance, and transpiration while lowering lipid peroxidation and antioxidant enzyme activities. Conversely, RL and RBL treatments notably decreased plant biomass and gas exchange parameters while elevating antioxidant enzyme activity [40] (Figure 1). These groundbreaking findings solidify blue light's role in sustainable, large-scale _C. sativa_ production, though further research is crucial to unravel the precise mechanisms through which light governs _C. sativa_ growth and development. The rooting of stem cuttings is a cornerstone of plant propagation, profoundly influenced by endogenous auxins, particularly indole-3-acetic acid (IAA) [71; 72]. IAA, produced in the shoot apical meristem or young leaves, is transported to the base, sparking cell division and adventitious root formation (Figure 1) [71; 72]. Light is critical in this process, supplying energy for photosynthesis and signaling photomopropenesis. However, high radiation can devastate auxin levels [73]. Far-red light (700-800 nm) stands out by boosting endogenous auxin accumulation via phytochromes, igniting shade avoidance responses, and enhancing auxin synthesis and stem elongation [73]. A revolutionary study on medicinal cannabis delved into the effects of different light spectra (blue, red, far-red) on the adventitious rooting of stem cuttings and their relationship with endogenous auxin and carbohydrates [56]. The study's revelations were profound: far-red light dramatically improved rooting in one of two experiments, particularly when combined with red or red-blue light [46] (Table 1). Notably, far-red light applied during the initial rooting stage was sufficient to enhance rooting without triggering excessive stem elongation. While the positive effects of far-red on auxin and carbohydrate concentrations likely underline the improved rooting, the study did not find a direct correlation between these factors and rooting success (Figure 1) [46]. These powerful findings underscore the potential of optimizing light spectra for both industrial _C. sativa_ production and medicinal cannabis propagation, heralding a new era of unparalleled efficiency and effectiveness in cultivation practices. Until recently, clonal cannabis propagation primarily relied on fluorescent lighting [74]. The shift to LEDs marks a revolutionary advancement, allowing cultivators to implement precise spectral treatments that enhance rooting and drastically cut energy consumption [74]. A groundbreaking study explored the effects of various LED combinations--blue (B), red (R), ultraviolet-A (UVA), and phosphor-converted white (W)--against a fluorescent (F) control on vegetative stem cuttings of 'Gelato-27', 'Grace', and 'Meridian'.