A light spectrum in the scope of 400 to 700nm induces growth and development, and UV (100–400nm) and infrared (700–800nm) light play a role in plant morphogenesis—which is essentially the process of plants developing their physical form and external structure. Optimizing Your Knowledge in the Grow Room To maximize your yield, always aim for 40 moles, or 40,000,000 μmol, per day. Here is how much PPFD is needed per second for each phase of cannabis growth to achieve the DLI of 40 moles of light per day. Seedling phase (18hr cycle): 200–300 μmol m-2 s-1 Vegetative phase (18hr cycle): 617 μmol m-2 s-1 Flowering phase (12hr cycle): 925 μmol m-2 s-1, (1500 μmol m-2 s-1 @2000ppm co2) (ballpark) When choosing grow lights for cannabis, it is essential to check the technical specifications to determine if they are strong enough to get the job done. Of course, this doesn't mean that you have to buy the most expensive lights there are. Still, it does mean that you should research each of these specifications in relation to your cannabis plants to find a grow light that will fully serve your needs. This is especially true with PPFD, as this is arguably the most insightful value for growers—it tells you exactly how much useful light your plants are absorbing at a certain distance from the grow light. With my fixed light source, as the plant develop height through stages, it will naturaslly grow into higher μmol ranges naturally dictated by its height. Look forward to filling the tent for the next grow. Last week will see increased blues. ELONGATED HYPOCOTYL5 (HY5), a bZIP-type transcription factor, acts as a master regulator that regulates various physiological and biological processes in plants such as photomorphogenesis, root growth, flavonoid biosynthesis and accumulation, nutrient acquisition, and response to abiotic stresses. HY5 is evolutionally conserved in function among various plant species. HY5 acts as a master regulator of a light-mediated transcriptional regulatory hub that directly or indirectly controls the transcription of approximately one-third of genes at the whole genome level. The transcription, protein abundance, and activity of HY5 are tightly modulated by a variety of factors through distinct regulatory mechanisms. This review primarily summarizes recent advances in HY5-mediated molecular and physiological processes and regulatory mechanisms on HY5 in the model plant Arabidopsis as well as in crops. Plants utilize light as the predominant energy source for photosynthesis. Besides, light signal acts as an essential external factor that mediates a variety of physiological and developmental processes in plants. Plants are continuously exposed to dynamically changing light signals due to the daily and seasonal alternation in natural conditions. The various light signals are perceived by at least five classes of wavelength-specific photoreceptors including phytochromes (phyA-phyE), cryptochromes (CRY1 and CRY2), phototropin (PHOT1 and PHOT2), F-box containing flavin binding proteins (ZTL, FKF1, and (LKP2), and UV-B RESISTANCE LOCUS 8 (UVR8). These photoreceptors are biologically activated by various light signals, subsequently initiating a large scale of transcriptional reprogramming at the whole genome level. Extensive genetic and biochemical studies have established that the ELONGATED HYPOCOTYL5 (HY5), a bZIP-type transcription factor, tightly controls the light-regulated transcriptional alternation. Loss of HY5 function mutant seedlings display drastically elongated hypocotyls in various light conditions, suggesting that HY5 acts downstream of multiple photoreceptors in promoting photomorphogenesis in plants. In addition to inhibiting hypocotyl growth, HY5 regulates other various physiological and developmental processes including root growth, pigment biosynthesis and accumulation, responses to various hormonal signals, and low and high temperatures. This review summarizes the recent advances and progress in HY5-regulated cellular, physiological, and developmental processes in various plant species. We also highlighted emerging insights regarding the HY5-mediated integration of multiple developmental, external, and internal signaling inputs in the regulation of plant growth. Among the genes regulated by the circadian clock, we found that the excision repair protein XPA is controlled by the biological clock, and we, therefore, asked whether the entire nucleotide excision repair oscillates with daily periodicity. XPA transcription and protein levels are at a maximum at around 5 pm and at a minimum at around 5 am. Importantly, the entire excision repair activity shows the same pattern. This led to the prediction that mice would be more sensitive to UV light when exposed at 5 am (when repair is low), compared to 5 pm (when repair is high). We proceeded to test this prediction. We irradiated two groups of mice with UV at 5 am and 5 pm, respectively, and found that the group irradiated at 5 am exhibited a 4–5 fold higher incidence of invasive skin carcinoma than the group irradiated at 5 pm. Currently, we are investigating whether this rhythmicity of excision repair exists in humans. Molecular mechanism of the mammalian circadian clock. CLOCK and BMAL1 are transcriptional activators, which form a CLOCK-BMAL1 heterodimer that binds to the E-box sequence (CACGTG) in the promoters of Cry and Per genes to activate their transcription. CRY and PER are transcriptional repressors, and after an appropriate time delay following protein synthesis and nuclear entry, they inhibit their own transcription, thus causing the rise and fall of CRY and PER levels with circa 24-hour periodicity (core clock). The core clock proteins also act on other genes that have E-boxes in their regulatory regions. As a consequence, about 30% of all genes are clock-controlled genes (CCG) in a given tissue and hence exhibit daily rhythmicity. Among these genes, the Xpa gene, which is essential for nucleotide excision repair, is also controlled by the clock. Circadian control of excision repair and photocarcinogenesis in mice. The core circadian clock machinery controls the rhythmic expression of XPA, such that XPA RNA and protein levels are at a minimum at 5 am and at a maximum at 5 pm. The entire excision repair system, therefore, exhibits the same type of daily periodicity. As a consequence, when mice are irradiated with UVB at 5 am they develop invasive skin carcinoma at about 5-fold higher frequency compared to mice irradiated at 5 pm when repair is at its maximum. The mouse in the picture belongs to the 5 am group with multiple invasive skin carcinomas at the conclusion of the experiment.