## 3 Light Effect on Growth and Development of _C. sativa_  
### Light Spectrum in Cannabis Growth, Development, and Metabolism  
The pivotal role of light's quality (spectral) composition in plant growth and physiological functions has been paramount since the dawn of photosynthesis research [32]. Recently, this field has exploded with intensity due to revolutionary advancements in computer-controlled lighting systems and the sophisticated documentation of photosynthetic activity. These strides are fortified by groundbreaking insights into the molecular mechanisms of photo regulation, governed by an array of photoreceptors and pigment systems [32]. The profound impact of varying light spectra is rooted in (i) the precise activation of distinct photoreceptors, (ii) the disparate efficiency of spectral components in driving robust photosynthesis, and (iii) the varying depth of spectral penetration into plant foliage (Figure 1) [32]. These dynamic factors orchestrate chloroplast movements, optimize light capture, and elevate photosynthetic capacity and metabolic processes [32]. Blue light, for example, dramatically boosts the biosynthesis of chlorophyll \(a\), and alters the Chl \(a/b\) ratio by regulating key gene expressions [33]. The synthesis and catabolism of proline, a critical compound for stress adaptation and redox balance, are also profoundly influenced by light quality [17; 34; 35]. Carbohydrate concentration, a vital indicator of cell division activity, is powerfully correlated with the intensity of photosynthetically active radiation (PAR) (Figure 1) [36; 35]. Blue light dramatically enhances total soluble carbohydrates (TSC) and starch accumulation, while red-blue light treatments significantly boost both fresh and dry biomass in plants. Blue light (400-500 nm) typically results in smaller, more compact leaves and shorter stems. Greenlight (510-585 nm) effectively mitigates lower leaf loss, whereas red light (620-700 nm) can inhibit flowering [37]. In stark contrast, a combination of red and far-red light (700-780 nm) forcefully triggers flowering and elongates leaves and stems [37; 38]. A low red-to-far-red light ratio deactivates phytochrome b, spikes gibberellin (GA) levels, and obliterates DELLA proteins. Despite its detrimental impact on quantum yield, supplemental UV-A radiation can dramatically elevate photosynthetic rates and biomass accumulation in _C. sativa_[37; 39]. Blue light profoundly influences chlorophyll biosynthesis, plant height, and stomatal opening while driving the accumulation of phenylpropanoid-based compounds without altering the plant morphology of the _C. sativa_ plant [40]. Red light, however, drastically transforms plant morphology and physiology, vigorously stimulating stem growth and flowering but failing to enhance secondary metabolism [40]. The precise balance of blue to red light is crucial for maximizing growth, pigment production, and antioxidant capacity in vegetable plants, although this balance is species-specific [40]. Plants exhibit species-specific responses to light stress, mediated by a diverse array of photoreceptors. Red light markedly boosts stomatal conductance, net photosynthesis, intercellular CO\({}_{2}\) levels, and transpiration rates, while blue light suppresses these parameters by inducing stomatal closure [40]. A combination of red and blue light can severely stifle growth and photosynthesis in _C. sativa_, increasing MDA and proline content, and protecting cellular organelle membranes (Figure 1) [40]. The spectrum of light withelds profound power over photosynthesis, directly and indirectly altering leaf structure, size, senescence rate, photosynthetic transport, stomatal conductance, and chlorophyll composition [41]. Blue light, in particular, exerts a significant influence on plant height, stomatal opening, circadian rhythms, photomorphogenesis, flowering time, and chlorophyll biosynthesis [42]. Despite the widespread practice of indoor _C.