## 3 Light Effect on Growth and Development of _C. sativa_
### Light Spectrum in Cannabis Growth, Development, and Metabolism
The adaptability of _C. sativa_ through significant physiological and biochemical changes was rigorously studied under 10 different LED light spectra (a combination of red, blue, green, far-red, UV, and natural light) using an advanced aeroponic system [32]. The R7/B2 light treatment propelled cannabidiol (CBD) levels to unprecedented heights, coupled with an increased photosynthetic rate and substantially lower levels of reactive oxygen species, total phenols, flavonoids, DPPH radical scavenging capacity, and antioxidant enzyme activities (Figure 1) [32]. Under these conditions, THC and CBD showed minimal stress responses, while THCA emerged as the primary stress marker, closely followed by CBDA. Notably, CBD concentrations surged under treatments L4 (R7), L5 (R7), and L8 (R5/B2/G1), with THC levels consistently surpassing those under natural light across all spectra. CBDA (cannabidiolic acid) synthesis peaked in L3 (R8), L4 (R7/B2), L6 (R6/B2/G1), and L8. The L4 treatment delivered staggering concentrations of CBD, CBDA, THC, and THCA while minimizing stress markers. In stark contrast, L6 resulted in lower CBD and THC but higher THCA and CBDA, alongside intensified stress response activity [62]. Green light emerged as a pivotal factor in CBD and CBDA synthesis, with far-red and UV-A light displaying complex, nuanced effects. Photosynthetically active radiation spans 400 to 700 nm, with red (600-700 nm) and blue (420-450 nm) wavelengths yielding the most significant influence due to their optimal absorption by chlorophyls a and b, complemented by carotenoid absorption (Figure 1) (Table 1) [62]. Recent revelations suggest that a full spectrum (white light) dramatically outperforms monochromatic red and blue lights in promoting plant growth and functionality [62]. LED light spectra profoundly impacted every measured morphological, physiological, and chemical parameter [62] (Table 1). The zenith of inflorescence yields was achieved under red and blue light at a 1:1 ratio, with similar success observed at a 1:4 blue/red ratio in two of the three varieties tested [15]. Conversely, white light with a 1:1 blue ratio yielded the lowest output. Light spectrum intricately shaped the chemical profile, with CBGA showing the most robust response, particularly under blue-rich light compared to far-red-rich HPS light [15]. Major cannabinoids like CBDA, THCA, and CBCA (cannabichromene acid) were also significantly affected, although responses were cultivar-specific and less pronounced than for CBGA. Blue light unequivocally promoted compact plant morphology, surpassing the influence of red/blue ratios (Table 1) [15]. The study uncovered cultivar-dependent responses, highlighting genetic variance and unveiling new avenues for breeding cannabis varieties optimized for light-induced responses [15]. Water relations and oxidative stress parameters remained largely unaffected by light quality across all varieties, underscoring the minimal impact of light spectra on _Cannabis_ water relations [15]. The full spectrum light significantly enhanced inflorescence yield compared to blue/red light, reinforcing the hypothesis that the light spectrum is a powerful tool for manipulating plant development and cannabinoid profiles, offering unparalleled opportunities to fine-tune cannabis and cannabinoid production (Table 1) [15]. These findings illuminate the transformative potential of strategically optimized light spectra in revolutionizing _Cannabis_ cultivation, maximizing both yield and cannabinoid content while effectively managing plant stress responses. This paradigm shift in horticultural practices paves the way for unprecedented advancements in the efficiency and potency of _Cannabis_ production.